zespri scientific pack kiwifruit scientifi… · • strategic research and scientific advisory...

Zespri® Scientific Pack Nutrition

& Health Attributes of Kiwifruit

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Index

Zespri® Research ............................................................................................................................................................................................. 03 • Introduction ...........................................................................................................................................................................................05• Zespri® Scientific Activities ............................................................................................................................................................05• Strategic Research and Scientific Advisory Steering Group .....................................................................................06• Regulatory Relationships .................................................................................................................................................................07• International Research Partnerships ........................................................................................................................................07

Nutrient Richness .......................................................................................................................................................................................... 09• Zespri® Kiwifruit Consistently Rank as One of the Most Nutrient Rich Fruits ...............................................11 • Kiwifruit Has a High Vitamin C Content .................................................................................................................................15• Kiwifruit Facilitates Iron Uptake .................................................................................................................................................16• Kiwifruit is Rich in Fibre ...................................................................................................................................................................16• Kiwifruit is a Good Source of Potassium ................................................................................................................................17• Kiwifruit Has a High Level and Variety of Antioxidant Vitamins and Phytonutrients ..................................18• Kiwifruit is a Natural Source of Folate .....................................................................................................................................19• Conclusions .............................................................................................................................................................................................20• References ................................................................................................................................................................................................21

Digestive Health ..............................................................................................................................................................................................23• Common Digestive Disorders Cause Significant Discomfort ...................................................................................25• Kiwifruit Components Effect on Gastric and Intestinal Digestion .......................................................................26• Kiwifruit as a Digestive Aid: What is the Evidence? ......................................................................................................29• Upcoming Research ...........................................................................................................................................................................35• Conclusions ............................................................................................................................................................................................36• References ...............................................................................................................................................................................................37

Vitamin C and Health ..............................................................................................................................................................................39• Vitamin C is an Essential Vitamin that Cannot Be Synthesised by the Human Body ...............................41• Vitamin C Has an Important Role in Human Metabolic Processes .......................................................................42• How Much Vitamin C Do We Need? .........................................................................................................................................43• One Zespri® Kiwifruit a Day Gives the Daily Requirement of Vitamin C ...........................................................44• Zespri® Kiwifruit is Very Effective at Increasing Plasma Levels of Vitamin C .................................................44• Kiwifruit and Vitamin C-Related Health: What is the Evidence? ...........................................................................45• Upcoming Research ...........................................................................................................................................................................55• Conclusions ............................................................................................................................................................................................56• References ...............................................................................................................................................................................................57

Metabolic Health ............................................................................................................................................................................................59• Kiwifruit Has a Low Glycaemic Index .....................................................................................................................................61• Kiwifruit Modulates Carbohydrate Digestion and Absorption ................................................................................62• The Glycaemic Response Per Kiwifruit Is Low ...................................................................................................................62• Kiwifruit Can Help Manage Blood Sugar Levels in People With Diabetes ............................................................63• Kiwifruit Affects Gut Microbiota ................................................................................................................................................63• Kiwifruit and Metabolic Health: In Vitro and In Vivo Studies .....................................................................................63• Upcoming Research ...........................................................................................................................................................................65• Conclusions ............................................................................................................................................................................................66• References ...............................................................................................................................................................................................67

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Nutrition and Health Attributes of Kiwifruit

Zespri® Research

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Introduction

Welcome to the Zespri® Scientific Pack, where you will find a high-quality body of evidence on the nutrition and health attributes of kiwifruit. At Zespri® we believe in the integrity of our product, and in order to build trust with our loyal consumers, we know the importance of demonstrating the scientific efficacy of our kiwifruit.

This Scientific Pack provides authorities, health advocates and the scientific community with an overview of evidence-based findings on the nutritional profile and health benefits associated with consumption of kiwifruit, including underpinning fundamental science explaining the mechanisms of observed outcomes. The pack includes current and emerging data in four core areas: • Nutrient Richness • Digestive Health • Vitamin C and Health • Metabolic Health

Zespri® Scientific Activities

In 2008, Zespri® put in place a world-class health and nutrition research programme around the health benefits of kiwifruit by joining forces with the Riddet Institute to form the Strategic Research and Scientific Advisory (SRSA). The Riddet Institute is a New Zealand government-funded Centre of Research Excellence with a widely acknowledged international standing.

The main aims of the SRSA are to ensure that Zespri® research projects are independently reviewed by experienced and respected scientists in the nutrition and health field. The projects are considered for their fit with the overarching Zespri® Health Strategy and the SRSA also reviews the scientific protocols and ensures that the research provider is the best science team for the required work. The composition of the steering group has been carefully put together to cover the range of activities that we are working on, such as laboratory-based research, animal model research and human clinical trials.

Zespri® Research

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Strategic Research and Scientific Advisory Steering Group

Dr Juliet AnsellDPhil (Oxon):Innovation Leader Health & Nutrition at Zespri International Ltd

Dr Jocelyn EasonBSc, PhD, MBA: General Manager Food Innovation at Plant & Food Research

Dr Véronique ParmentierBSc, PhD:Global Health Marketing Manager at Zespri International Ltd

Dr Abby Thompson PhD, BTech: Director of Riddet Innovation at Massey University

Professor Richard GearryMBChB, FRACP, PhD: Professor of Medicine at the University of Otago

Professor David RichardsonBSc, MSc, PhD, FIFST, FRSM: Specialist Consultant in Nutrition and Food Science

Lynley DrummondBSc: Strategy, Innovation & Science advisor at Drummond Food Advisory Ltd

DistinguishedProfessor Paul MoughanBAgrSc (Hons), PhD, DSc, Hon DSc, FRSNZ, FRSC: Co-director of the Riddet Institute at Massey University

Carol WardGeneral Manager Marketing at Zespri International Ltd

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Although all projects pass by the SRSA board for scientific merit and strategic fit, the ongoing clinical trial project management and troubleshooting is carried out by a smaller team. This consists primarily of Professor David Richardson, Professor Richard Gearry, Lynley Drummond and Dr Juliet Ansell, with principal investigators for each country involved in protocol development and ongoing trial management.

Figure 1. Overarching Zespri® Business Strategy

Zespri® has established a number of research partnerships in New Zealand and internationally, who provide world class input into nutrition and health science.

Zespri® works in accordance to European Food Safety Authority (EFSA) guidelines and the Australia New Zealand Food Standards Code and in conjunction with the Ministry for Primary Industries, New Zealand.

International Research Partnerships

Regulatory Relationships

Scientific Peer Review

Quarterly meetings of the SRSA board review on merit and strategic fit.

Research Provider Engagement

Proposal sought by Innovation Leader: non-competitive.

Scientific Business Approval

Bi-monthly review of new projects for financial approval

with consideration of strategic priorities and

commercial return.


Nutrient Richness

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Zespri® Kiwifruit Consistently Rank as One of the Most Nutrient Rich Fruits

Kiwifruit is known as a nutritionally dense fruit based on the level of nutrients present (Table 1)1. With nutrient adequacy scores of 18.8 and 11.4, Zespri SunGold and Zespri Green kiwifruit, respectively, have the highest nutritional value score among the most popular fruit varieties (Breakout box 1; Figure 1). Kiwifruit are also relatively low in calories and consequently their consumption is appropriate in weight control diets.

Nutrient Richness

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Table 1. Nutrient content of Zespri SunGold and Zespri Green kiwifruit

Nutrient Units/100 g Edible Flesh

Zespri® Green* Zespri® SunGold**

Proximates Water g 83.5 82.4

(EC) EU † Energy kcal 81 79

(USDA) US † Energy kcal 57 63

Protein g 1.2 1.02

Total lipid (fat) g 0.7 0.28

Ash g 0.65 0.47

Carbohydrate, available g 9.1 15.8

Fibre, total dietary g 3 1.4

Sugars, total g 8.8 12.3

Minerals Calcium, Ca mg 27 17

Iron, Fe mg 0.2 0.21

Magnesium, Mg mg N/A 12

Phosphorus, P mg 34 25

Potassium, K mg 300 315

Sodium, Na mg 2.3 3

Zinc, Zn mg 0.1 0.08

Copper, Cu mg N/A 0.151

Manganese, Mn mg N/A 0.048

Selenium, Se µg 0.6 0.4

Vitamins Vitamin C, total ascorbic acid mg 85.1 161.3

Vitamin B1 - thiamin mg 0 0

Vitamin B2 - riboflavin mg 0.05 0.074

Vitamin B3 - niacin mg 0.83 0.231

Vitamin B5 - panthothenic acid mg N/A 0.12

Vitamin B6 - pyrridoxine mg 0.07 0.079

Vitamin B9 - folate (DFE) µg 38 31

Choline mg N/A 1.9

Vitamin B12 µg 0 0.08

Vitamin A µg 9 N/A

Vitamin A, retinol activity equivalents (RAE)

µg N/A 1

Vitamin A IU N/A 23

Vitamin E - a-tocopherol mg 0.86 1.4

Vitamin K µg N/A 6.1

Other Carotene, beta µg 54 14

Lutein + zeaxanthin µg N/A 24

NUTRIENT ADEQUACY SCORE 11.4 18.8

NUTRIENT DENSITY /100 kcal 20 29.8

GLYCAEMIC INDEX 39 38

Sources of data* Crop & Food Research, New Zealand Nutrient composition of New Zealand Zespri Green kiwifruit, 2015. ** Combined data from NVIG2010, Japan market analysis 2010 and ZESPRI analysis 2011.† There are a number of equations to calculate energy as noted by the European Commission (2014) and USDA (2009). The first line in the table refers to the European Commission legislature that calculates energy as total carbohydrate plus fibre http://ec.europa.eu/food/safety/labelling_nutrition/labelling_legislation/index_en.htmThe second line in the table refers to USDA legislature that calculates energy as total carbohydrate by difference minus insoluble fibre http://www.fda.gov/food/guidanceregulation/guidancedocumentsregulatoryinformation/labelingnutrition/ucm2006828.htm Nutrient Adequacy Score and Nutrient Density calculated based on the methods of Darmon N, et al. A Nutrient Density Standard for Vegetables and Fruits: Nutrients per Calorie and Nutrients per Unit Cost. J Am Diet Assoc 2005:105:1881-7

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Figure 1. Zespri® kiwifruit has the highest nutrient adequacy score of commonly eaten fruits2

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18.8Zespri SunGold Kiwifruit

11.4 Zespri Green Kiwifruit

8.0 Strawberry

4.9 Banana

3.7 Cranberry

2.9 Blueberry

2.1 Pear

8.1Orange

7.0Lemon

4.8Pomegranate

3.6Melon

2.4Grape

2.1Watermelon

Based on the method of Darmon N, et al (2005)2

1.8 Apple

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Figure 2. Health benefits of kiwifruit

Breakout box 1: Nutrient adequacy score

The nutrient adequacy of a certain food refers to how many nutrients it provides relative to its weight. This is different to the nutrient density of a food, which refers to how many nutrients it provides relative to the number of calories it contains.

A nutrient adequacy score is determined as the mean percentage of daily values (amount per 100 g / recommended dietary allowance [RDA]) of 17 selected nutrients, including: protein, fibre, calcium, iron, magnesium, potassium, zinc, vitamin C, thiamin (vitamin B1), riboflavin (vitamin B2), niacin, pantothenic acid, pyridoxine (vitamin B6), folic acid, vitamin B12, vitamin A and vitamin E.

The high amount of vitamin C in kiwifruit is the primary driver of its high nutrient adequacy score1. Other key nutrients include fibre, folate, potassium and vitamin E1. Kiwifruit also contains a wide variety of antioxidants, phytonutrients and enzymes with known digestive benefits, and is low in calories, containing just 57 kcal/100 g1. The combination of all these unique attributes works within the body to provide significant health benefits (Figure 2)1.

FIBRE

• Digestive health

VITAMIN C

• Immune system function• Reduces tiredness and fatigue• Helps normal collagen formation

C

FOLATE

• Pregnancy • Reduces tiredness and fatigueB9

LOW GLYCAEMIC INDEX

• Glucose toleranceGI

POTASSIUM

• Heart activity and fluid balanceK

PHYTONUTRIENTS& ANTIOXIDANTS

• Defence against cell damage • Cardiovascular health

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Kiwifruit Has a High Vitamin C Content

Zespri® kiwifruit is one of the best sources of vitamin C among fruits and vegetables (Figure 3). Zespri SunGold kiwifruit contains 161.3 mg/100 g of vitamin C, almost three times the amount of vitamin C found in oranges and strawberries, traditionally known as good sources of vita-min C, while Zespri Green kiwifruit contains 85.1 mg/100 g3. More information on the role of vitamin C in kiwifruit can be found in the Vitamin C and Health section of this Scientific Pack.

Figure 3. Graph comparing the vitamin C content of various fruits with Zespri® kiwifruit3

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4.6 4.014

53.258.8

26.718.0

9.7 4.3 8.1 10.2

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* USDA Nutrient Database 2015 (Release 28) ** New Zealand FOODfiles 2014 Version 01

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Kiwifruit Facilitates Iron Uptake

High levels of vitamin C in kiwifruit can improve iron uptake

Poor iron status remains one of the most common micronutrient concerns globally. In a study of individuals with low iron status (serum ferritin [SF] ≤25 μg/l and haemoglobin [Hb] ≥115 g/L), eating kiwifruit with an iron-fortified breakfast cereal was found to increase iron status4, 5. In this study, 89 healthy women were randomised to receive iron-fortified breakfast cereal, milk and either two Zespri Gold kiwifruit or one banana at breakfast every day for 16 weeks. After 16 weeks, median serum ferritin significantly increased from 17.0 μg/l at baseline to 25.0 μg/l, compared to the banana group who had a median serum ferritin of 16.5 μg/l at baseline that rose to 17.5 μg/l at the end of the study (p<0.001)5. Importantly, the 10.0 μg/l increase in serum ferritin in the women who ate kiwifruit increased levels to within the normal reference range of 20–160 mg/l5. Additionally, median soluble transferrin receptor concentrations significantly decreased by –0.5 mg/l for kiwifruit versus 0.0 mg/l for banana (p=0.001)5.

Kiwifruit is Rich in Fibre

Kiwifruit has been found to improve various digestive functions due to its fibre content (1.4–3 g/100 g; Figure 4). Kiwifruit fibre consists of both soluble and insoluble fibre at a ratio of approximately 1:4 in Green kiwifruit and 1:3 in SunGold6. The soluble fibre fraction contains almost exclusively pectic polysaccharides that have the ability to retain water and form gels. This increases the size and softness of the stools and helps stimulate bowel movements, faci-litating intestinal transit through the digestive system7. The insoluble fibre fraction is mostly cellulose and hemicelluloses, which make up the structural parts of plant cell walls, with small amounts of pectin. A major role of insoluble fibre is to add bulk to the stools, aiding movement through the digestive tract7. More information on the role of fibre in kiwifruit can be found in the Digestive Health section of this Scientific Pack.

Figure 4. Fibre content of Zespri® kiwifruit compared to other fruit3


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Figure 5. Potassium content of Zespri® kiwifruit compared to other fruit3

* USDA Nutrient Database 2015 (Release 28) **New Zealand FOODfiles 2014 Version 01

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Kiwifruit is a Good Source of Potassium

Potassium is an important mineral for the development of many different body functions8. In particular, it:

• Contributes to the normal function of the nervous system.• Is necessary for muscular contraction.• Contributes to the maintenance of normal blood pressure.

Fresh foods such as fruits, green vegetables and cereals or wholemeal bread are generally high in potassium and low in sodium. The daily recommended value for potassium is 3500 mg3. Zespri® kiwifruit contains 301–315 mg/100 g potassium, which is roughly equivalent to the amount of potassium in a banana (Figure 5).

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Kiwifruit Has a High Level and Variety of Antioxidant Vitamins and Phytonutrients

Antioxidants are substances that may prevent or delay some types of cell damage9,10. They do this by blocking some of the damage caused by free radicals, unstable molecules created every day during normal metabolism that damage DNA.

Kiwifruit contains a wide range of natural antioxidants, such as vitamin C, vitamin E, polyphenols and flavonoids (compounds derived from polyphenols)1. Research has shown a significant increase in plasma antioxidant levels following the consumption of kiwifruit compared to the consumption of other fruits and foods11. While vitamin C is generally regarded as the most important antioxidant of kiwifruit, vitamin E and the polyphenols and flavonoids present in both Zespri Green and Zespri SunGold kiwifruit also have an antioxidant effect. There is strong evidence showing that eating foods with polyphenolic compounds contributes to good overall health12.

Vitamin E is the generic term for a group of eight plant-derived, fat-soluble and structurally related compounds belonging to two main families – the tocopherols and tocotrienols. Natural and naturally derived tocopherols occur only in a single form (RRR, also known as alpha- or delta-tocopherol). Vitamin E is the body’s primary lipid-soluble antioxidant defence against free-radical-induced cell damage13.

Vitamin E levels in Zespri SunGold are relatively high compared to other fruits, at 0.9–1.4 mg/100 g. This is important because in general, fruit are poor sources of vitamin E, with the exception of avocado. However, unlike avocado, kiwifruit is one of the few low-fat sources of vitamin E.

Phytonutrients are bioactive plant-derived compounds that are associated with positive health effects. Phenolic phytochemicals are the largest category of phytochemicals; the three most important groups of dietary phenolics are flavonoids, phenolic acids, and polyphenols14. Kiwifruit contains various phytochemicals, such as phenolic acids and flavonols,13 which are thought to protect DNA in the nucleus of human cells from oxygen-related damage via a dual protective role: decreasing DNA oxidation damage and enhancing removal of the damage that does occur1.

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Figure 6. Folate content of Zespri® kiwifruit compared to other fruit3


Kiwifruit is a Natural Source of Folate Folate is an essential nutrient for cellular growth and development, and is vital for the formation of the erythrocytes (red blood cells) that transport oxygen, iron and other minerals15. Folate performs important functions in the healthy body, and sufficiently high levels are needed before and during pregnancy. It is also vital for infant growth. Some of its contributions are as follows7, 15:

• Growth of tissue during pregnancy

• Normal formation of amino acids

• Normal formation of blood cells

• Normal formation of homocysteine

• Normal psychological function

• Reduction of tiredness and fatigue

• Process of cell division

As cooking destroys folate, fresh kiwifruit is a good source of folate, compared to for example cooked green vegetables. The daily recommended value for folate is 400 μg. During pregnancy, it is very difficult to meet folate requirements with food alone. Zespri® kiwifruit contains 31–38 μg/100 g folate, making it a useful complement to folic acid supplements in pregnant women (Figure 6).

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Conclusions

• Zespri® kiwifruit is consistently one of the most nutrient-rich fruit available, driven primarily by the high vitamin C content. The high levels of vitamin C in kiwifruit can assist the body’s uptake of iron.

• Zespri® kiwifruit contains high level and variety of antioxidants and phytonutrients, such as vitamin C, vitamin E, polyphenols and flavonoids. These compounds reduce the amount of oxidative damage to the cells of the body and improve the repair of damaged DNA caused by free radicals and oxidative stress.

• Zespri® kiwifruit is a good source of potassium.

• Zespri® kiwifruit is rich in fibre, which contributes to good digestive health improving bowel habits and stimulating the growth of beneficial bacteria in the gut.

• Zespri® kiwifruit is a natural source of folate.

• The combination of vitamins, minerals, laxative effects and benefits for improving iron uptake makes kiwifruit an excellent fruit during pregnancy.

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References

1. Boland M, Moughan PJ. Advances in food and nutrition research. Nutritional benefits of kiwifruit. Waltham, MA: Elsevier Inc; 2013.

2. Darmon N, Darmon M, Maillot M, Drewnowski A. A nutrient density standard for vegetables and fruits: nutrients per calorie and nutrients per unit cost. J Am Diet Assoc. 2005;105:1881-7.

3. USDA. USDA national nutrient database for standard reference (release 28). 2015.

4. Beck K, Conlon C, Kruger R, Coad J, Stonehouse W. The effect of gold kiwifruit consumed with an iron fortified breakfast cereal meal on iron status in women with low iron stores: A 16 week randomised controlled intervention study. BMC Public Health. 2010;10:36.

5. Beck K, Conlon CA, Kruger R, Coad J, Stonehouse W. Gold kiwifruit consumed with an iron-fortified breakfast cereal meal improves iron status in women with low iron stores: A 16-week randomised controlled trial. Br J Nutr. 2011;105:101-9.

6. The New Zealand Institute for Plant & Food Research Limited. (2015). New Zealand Food Composition Database: New Zealand FOODfiles 2014 Version 01. Retrieved March 30, 2015 from http://www.foodcomposition.co.nz/foodfiles.

7. Sims IM, Monro JA. Fiber: Composition, structures, and functional properties. Adv Food Nutr Res. 2013;68:81-99.

8. European Commission. EU register on nutrition and health claims (2012).

9. Ginter E, Simko V, Panakova V. Antioxidants in health and disease. Bratisl Lek Listy. 2014;115:603-6.

10. National Institutes of Health. Antioxidants and health: An introduction. 2015.

11. Prior RL, Gu L, Wu X, Jacob RA, Sotoudeh G, Kader AA, Cook RA. Plasma antioxidant capacity changes following a meal as a measure of the ability of a food to alter in vivo antioxidant status. J Am Coll Nutr. 2007;26:170-81.

12. Kim EY, Ham SK, Shigenaga MK, Han O. Bioactive dietary polyphenolic compounds reduce nonheme iron transport across human intestinal cell monolayers. J Nutr 2008;138:1647-51.

13. Fiorentino A, D’Abrosca B, Pacifico S, Mastellone C, Scognamiglio M, Monaco P. Identification and assessment of antioxidant capacity of phytochemicals from kiwi fruits. J Agric Food Chem. 2009;57:4148-55.

14. King A, Young G. Characteristics and occurrence of phenolic phytochemicals. J Am Diet Assoc. 1999;99:213-8.

15. Bailey LB, Stover PJ, McNulty H, Fenech MF, Gregory JF 3rd, Mills JL, Pfeiffer CM, Fazili Z, Zhang M, Ueland PM, Molloy AM, Caudill MA, Shane B, Berry RJ, Bailey RL, Hausman DB, Raghavan R, Raiten DJ. Biomarkers of nutrition for development-folate review. J Nutr. 2015;145:1636S-1680S.


Digestive Health

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Digestive Health

Figure 1. Common gastrointestinal disorders

Common Digestive Disorders Cause Significant Discomfort

Gastrointestinal disorders are common conditions worldwide in adults and children, and can severely affect the individual’s quality of life and feeling of general wellbeing1. They may affect the upper gastric part of the digestive system or the lower intestinal area, and can cause a range of symptoms (Figure 1). These disorders generally result from lifestyle factors such as diet, hydration and exercise, from chronic illnesses such as diabetes, and from aging1. Current interventions for gastrointestinal conditions include lifestyle and dietary modifications as well as pharmacologic intervention, which may cause side-effects1.

Upper gastrointestinal disorders

• Gastric reflux • Stomach ache • Delayed gastric emptying • Nausea • Vomiting

Lower gastrointestinal disorders

• Constipation • Indigestion • Bloating • Diarrhoea

STOMACH

COLON

INTESTINES

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Figure 2. Digestive benefits of kiwifruit

Kiwifruit Components Effect on Gastric and Intestinal Digestion

Green kiwifruit are an excellent source of vitamins (A, C, and E), minerals (potassium), fibre and certain bioactive components, such as polyphenols and enzymes2. Kiwifruit has been found to improve various digestive functions at both the gastric and intestinal level. This is due to their relatively high fibre content (3 g/100 g in raw Zespri Green kiwifruit and 1.4 g/100 g in raw Zespri SunGold kiwifruit) and the presence of a natural digestive enzyme unique to kiwifruit known as actinidin, which breaks down proteins and facilitates gastric digestion2.

The substances found in kiwifruit have been shown to promote the effective digestion of dietary protein, increase faecal bulking and softness, and enable better lubrication, assisting the propulsion of contents along the colon (Figure 2)3. In addition to positive effects on gastric and intestinal digestion, kiwifruit are also associated with beneficial changes in gut microbiota (see Breakout box 1 and 2)2,4.

Upper gastrointestinal tract

• Facilitates gastric digestion• Reduces glucose absorption

rate • Potentially reduces symptoms

such as nausea and vomiting

Lower gastrointestinal tract

• Improves intestinal habits, reducing constipation

• Creates positive changes in intestinal enzymes that can serve as a natural defence

• Encourages the growth of beneficial bacteria, which inhibit harmful bacteria

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Breakout box 1: Microbiota

Human gut bacteria (microbiota) have co-evolved with us metabolically to live symbiotically and share the workload of extracting energy and nutrients from the diet. A healthy balance of gut microbiota is therefore essential for the breakdown of foods and for the production of vitamins. The dietary fibre and polyphenols found in kiwifruit can be degraded by various members of the gut microbiota and result in beneficial effects (Figure 3)2, 4-6. These gut microbiota can also affect the structure and function of the mucosal barrier in the colon, which prevents the influx of water soluble bacterial products and toxins from the colon into the blood7.

FibrePolyphenolsCarbohydrates

Health benefits

• Energy and nutrients for colonic cells and other good bacteria• Secretion of immune effector molecules which regulate proper immune function

Gut microbiota

Othermetabolites

Short chain fatty acids

OligosaccharidesPolyphenolmetabolites

Figure 3. The role of gut microbiota in the breakdown of food

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Prebiotics are food ingredients, generally of plant origin, that cannot be broken down by the human digestive system, such as soluble fibre. Instead, various members of the gut microbiota can degrade them. The breakdown of prebiotics selectively stimulates the growth or activity of ‘good’ bacteria in the colon. These bacteria include lactobacilli and bifidobacteria species, which are commonly included in probiotic foods and supplements.

What is the role of fibre in digestive health?

Fibre in kiwifruit is made up of soluble components (e.g. pectin) and insoluble components (e.g. hemicelluloses and celluloses, which make up cell walls)8. Soluble fibre has the ability to retain water and form gels, which increases the size and softness of the stools, and aids stimulation of peristaltic movements8. Insoluble fibres also enhance digestion by adding bulk to the stools, aiding movement through the digestive tract8.

There is some evidence to suggest that as the kiwifruit ripens, there is increasing solubilisation of insoluble fibre within the cell walls of kiwifruit. This results in a unique and greatly increased ability to hold water, causing a lubricating effect (Figure 4)9-11.

Figure 4. Water retention capacity of various fruit fibre8

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Applefibre

Orangefibre

Zespri Green fibre

Breakout box 2: Prebiotics

29

Collectively, these properties can help to improve the symptoms of constipation by8: • Increasing the frequency of bowel movements • Improving the type of stools • Reducing the sensation of bloating • Increasing satisfaction when moving the bowels • Reducing the time of intestinal transit

In the upper gastrointestinal tract, these same properties of kiwifruit fibre act to reduce the rate of glucose absorption so that the glycaemic response is lower and blood sugar levels remain stable8. This is important for people who are wanting to maintain a healthy weight and prevent a progression into obesity, and eventually metabolic diseases such as type 2 diabetes. It also increases the sense of fullness, since the fibre swells by taking up water and acts to increase viscosity, and animal trials have also shown that eating kiwifruit can have a positive effect on the rate of gastric emptying12.

What is the role of actinidin in digestive health?

Actinidin has been shown to enhance protein digestion in the stomach and the small intestine13, 14, potentially allowing faster and more complete digestion of food proteins. This improved digestion results in:

• A reduced sensation of heaviness associated with protein-rich foods • Improved protein absorption • Improved digestive comfort

It is proposed that actinidin or other compounds in kiwifruit may also act as modulators of gastric motility. It has been observed that after protein digestion with actinidin, potentially bioactive peptides may be produced from the food proteins. However, it is unknown if these have any effect on gastric motility15.

Kiwifruit as a Digestive Aid: What Is the Evidence?

Kiwifruit enhances protein digestion

In vitro studies have shown that actinidin, acting in combination with the gastric and intestinal enzymes pepsin and pancreatin, enhances protein digestion in both the stomach and the small intestine13, 14. In an in vitro study that examined the effect of actinidin on gastric protein digestion, a range of common protein sources derived from soy, meat, milk and cereals were incubated with a kiwifruit extract containing actinidin and pepsin at pH 1.9 (a simulation of gastric digestion in humans)13. Results showed that for milk, soy and meat protein sources, the presence of kiwifruit extract enhanced digestion to a greater extent than pepsin alone13.

In another in vitro study, a range of food proteins were studied to assess the proposition that actinidin influences the digestion of proteins in the small intestine14. Proteins from sources including soy, meat, milk, and cereals, were incubated in the presence or absence of actinidin with pepsin at stomach pH (stimulating gastric digestion) and then with added pancreatin at a pH to simulate small intestine digestion14. Actinidin was shown to influence the digestion patterns of each of the protein types to various extents. For some proteins, actinidin had little impact on digestion14. However, for whey, zein, collagen and wheat proteins, the presence of actinidin resulted in a substantially greater increase in digestion14.

IN VITRO STUDIES

30

Kiwifruit modifies colonic bacteria

A healthy balance of bacteria colonising the gastrointestinal tract (colonic microbiota) is essential for the breakdown and metabolism of foods as well as for the production of microbially synthesised vitamins. Interestingly, in vitro studies including some using a model gut system have demonstrated that components of kiwifruit are able to modulate colonic microbiota (Figure 5)5, 16-22. Nutrients known as polyphenolics may directly stimulate the growth of beneficial bacteria in the colon or act as antimicrobial agents against pathogens, while non-digestible polysaccharides (insoluble fibre) broken down by the microbiota may induce selective growth of beneficial bacteria19, 21.

*

Figure 5. Predominant bacterial groups after fermentation of kiwifruit and control food sources16

7.0

6.5

6.0

5.5

5.0

0 24

*

*

Time (h)

Bifi

doba

cter

ium

sp

p. (

log 10

cfu

/mL)

48

6.0

5.5

5.0

0 24

**

*

Time (h)

Lact

obac

illu

s sp

p. (

log 10

cfu

/mL)

48

Control Gold kiwifruit Green kiwifruit Inulin

The values represent mean log10 cfu/ ml±standard error, for 12 faecal fermentations, from the 10 donors.Means which were significantly different from the control at the corresponding time are marked with an asterisk

31

Kiwifruit modulates gut-mediated immune function

Kiwifruit has also been shown to enhance the production of antimicrobial peptides, an important part of the first line of defence at intestinal mucosal surfaces. Colonic epithelial cell studies in vitro have shown that human faecal microbial breakdown products from in vitro digested kiwifruit increased antimicrobial peptides human β-defensin 1 and 2 (HBD-1 and 2) production17. This could increase host protection against micro-organisms (see Breakout box 1).

IN VIVO STUDIES

Kiwifruit enhances protein digestion and gastric empting rate

The effects of actinidin on protein digestion has also been replicated in vivo. A recent study in rats showed that actinidin from green kiwifruit significantly increased the gastric digestion of beef muscle protein, gelatin soy protein and gluten by 27–60%23. A separate study in growing rats showed increased gastric protein digestion with dietary actinidin from kiwifruit, and also demonstrated an accelerated gastric empting rate for several dietary protein sources24. Authors of this study conclude that it is likely that gastric empting rate is affected by gastric protein digestion24.

These results were confirmed by an in vivo study investigating the effect of dietary actinidin on gastric digestion of beef muscle proteins and gastric empting rate in pigs12. Use of a positive sample of added actinidin and a negative control of inactivated actinidin demonstrated a significant increase in gastric digestion with the active substance when consumed with meat (25% with actinidin, 17% without actinidin). This demonstrates conclusively that actinidin is responsible for the enhanced gastric hydrolysis of food proteins. Stomach emptying rate was also faster when green kiwifruit were consumed with meat (half life for dry matter was 137 min with actinidin versus 172 min without actinidin)12.

Kiwifruit beneficially modulates colonic microbiota

In vivo studies have shown that kiwifruit products that reach the colon result in changes in microbial growth and by-product formation (see Breakout boxes 1 and 2). An in vivo study in growing pigs found that animals who had eaten green kiwifruit had a significantly higher number of ‘good’ bacteria in the colon, leading to an improved intestinal environment4. These results were also replicated in another in vivo study, where rats who were fed a diet of green and gold kiwifruit for 6 weeks demonstrated significantly increased populations of ‘good’ bacteria2. As well as increased colonic microbiota, the rats were found to have improved colonic barrier function by increased mucin expression and improved immune cell stimulation. These in vitro changes in microbiota suggest that regular and consistent kiwifruit consumption could positively influence colonic health2.

32

CLINICALSTUDIES

Kiwifruit contributes to gastric comfort following protein ingestion

In order to follow up on the promising results of the effects of actinidin on protein digestion in vitro and in vivo, a human clinical trial was conducted to examine its effect on gastric comfort following a protein meal25. In this study, 10 healthy adult males ate a meal of >400 g lean steak with 200 g kiwifruit containing either active or inactive actinidin. For all measures of gastric comfort (pain in upper abdomen, rumbling in stomach, bloating, belching, and flatulence) the men who ate the kiwifruit with active actinidin resulted in less symptoms25. For the symptom of ‘bloating’ this difference was statistically significant25.

Kiwifruit improves bowel functioning

There is growing evidence that kiwifruit has laxative properties, with several clinical studies demonstrating changes in bowel function in response to kiwifruit intake. In a study of 38 people, eating one kiwifruit/30 kg body weight for 3 weeks lead to increased frequency of defecation, higher volume of stool production, and greater softness of bowel motions26. In the second study, 33 chronically constipated patients were given two kiwifruit per day for 2 weeks27. Kiwifruit consumption significantly increased complete spontaneous bowel motion, improved transit time and rectal sensation, and decreased days of laxative use, compared with control subjects who were not given kiwifruit27. In the third study, the effect of kiwifruit intake on physiological bowel functions in 41 patients diagnosed with irritable bowel syndrome (IBS) was evaluated. Having eaten two kiwifruit per day for 4 weeks, participants significantly increased defecation frequency and decreased colon transit time28. Another study in a Mediterranean patient population suffering from functional constipation, demonstrated that the intake of three kiwifruit per day significantly improved the quality of evacuation (number of depositions, consistency and ease)29.

In a systematic review of clinical trials in which fresh kiwifruit were used for the treatment of constipation or functional bowel disorders, daily consumption of two kiwifruit was found to reduce symptoms associated with constipation, but did not adversely affect bowel habits in healthy non-constipated individuals (Table 1)30. Pooled data gave an increase in stool frequency of 1.6 per week when two kiwifruit were consumed, and a mean increase of 4.1 when three kiwifruit were consumed30.

Kiwifruit is suitable on a low FODMAP diet

Gastrointestinal symptoms associated with IBS can be triggered by poorly absorbed short chain carbohydrates. These carbohydrates can be fermented by bacteria in the colon releasing gases31-34 that stretches the bowel, causing bloating, wind and pain. They can also cause water to enter the colon, resulting in loose motions and diarrhoea. These short chain carbohydrates have been grouped together under the term FODMAPs which stands for Fermentable Oligo-, Di-, Mono-saccharides And Polyols (see Breakout box 3), and includes fructose (in excess of glucose), lactose, sugar polyols (sorbitol, mannitol), fructans and galacto-oligosaccharides (GOS). A diet low in FODMAPs is now often used to manage functional gastrointestinal symptoms in patients with IBS31, 35-38.

Interestingly, many fruits and vegetables are high in FODMAPs that can trigger abdominal symptoms in people with IBS. Kiwifruit, however, is a low FODMAP fruit39 as it has a balanced ratio of glucose to fructose, allowing fructose to be well absorbed. Kiwifruit can therefore be included as part of a low FODMAP diet for sufferers of IBS.

33

Table 1. Summary of findings from human clinical trials with fresh green kiwifruit 30

Reference and daily intervention

Country Population group

Study Quality

High Low

? Not able to assess

Frequency ↑, SS ↑, NSS

Stoolfrom

↑, SS ↑, NSS

? Not measured

Ease/comfort ↑, SS ↑, NSS

Transit time

↓, SS? Not measured

Side effects

none

Chan et al. (2007): two Zespri

Green kiwifruit

ChinaFunctional constipation

Chang et al. (2010): two Zespri Green kiwifruit

Taiwan

Irritable bowel syndrome with constipation

?

Hiele (2010): three Zespri Green kiwifruit

BelgiumFunctional constipation ?

Marzo & Cunillera (2015): three Zespri Green kiwifruit

SpainFunctional constipation ?

Ohsawa et al. (2010): two Zespri Green kiwifruit

JapanProne to constipation ?

Rush et al. (2002): pre trial, one Zespri Green kiwifruit per 30 kg bodyweight

New Zealand

Healthy ? ?

Rush et al. (2002): main trial, one Zespri Green kiwifruit per 30 kg bodyweight

New Zealand

Healthyelderly ?

SS= Statistically Significant | NSS = Not Statistically Significant

34

Breakout box 3: FODMAPs

FODMAPs (Fermentable Oligo-, Di-, Mono-saccharides And Polyols) are fermentable carbohydrates found in food that can cause digestive discomfort, especially for people with IBS. FODMAPs, which are poorly absorbed in the small intestine, pass through to the colon where they are fermented by bacteria, contributing to the production of gas. The FODMAPs are also highly osmotic and therefore attract water into the colon, which can alter how quickly the bowels move. These two processes can then trigger symptoms including abdominal pain, bloating, excessive wind, constipation or diarrhoea, or a combination of both.

Common high FODMAP foods include milk, apples, broccoli, wheat breads, cereals, pasta, avocados, pears, stone fruits, and mushrooms, among many more. A diet low in FODMAPs has been proven to be the most effective dietary therapy for IBS and symptoms of an irritable bowel31,35-38. The Monash University Department of Gastroenterology has developed a ‘Low FODMAP Certification Programme’ in order for people with medically diagnosed IBS to identify and select low FODMAP food choices. Certified low FODMAP products are listed in the Monash University low FODMAP diet booklet and app39. Kiwifruit is a low FODMAP food and listed as such in the FODMAP diet booklet and app.

35

Upcoming Research

Since early clinical studies were carried out in different countries and included different participant subgroups (e.g. in terms of age, health status, etc.), the lack of common protocol may have led to results that are not generalisable to the larger population. There was therefore a need for a large multinational study that enrolled a large group of participants with a range of digestive health conditions. A multi-country, randomised, cross-over, controlled, clinical intervention study is currently ongoing to evaluate the effect of Zespri Green kiwifruit on digestive and gut health function. The primary objective of this trial is to determine the efficacy of kiwifruit as a treatment for the relief of constipation and a reduction in gastrointestinal discomfort. In each participating country, 20 healthy people, 20 people with IBS with constipation (IBS-C) and 20 people with functional constipation (FC) will be recruited. The trial study design is presented below (Figure 6).

Figure 6 . Zespri® clinical intervention study design

2-week lead period

4-week washout period

2-week follow-up period

4-week kiwifruit intervention

4-week psyllium intervention

4-week psyllium intervention

4-week kiwifruit intervention

36

Conclusions

• Gastrointestinal issues are common conditions worldwide and can negatively affect an individual’s quality of life1.

• Green kiwifruit is a rich source of fibre, vitamins, minerals and certain bioactive components, and in vitro and in vivo studies have demonstrated beneficial effects on gastric and intestinal function2.

− The fibre content of kiwifruit can have a significant effect on digestion by increasing faecal bulking and softening, increasing lubrication of faecal matter and reducing glucose absorption rate, helping stabilise blood sugar levels.

− The enzyme actinidin, found uniquely in kiwifruit, improves digestive comfort by increasing the breakdown of proteins and facilitating gastric digestion.

− There is growing evidence that consumption of kiwifruit beneficially modulates the colonic microbiota, likely resulting in increased intestinal health and overall wellness.

• Clinical studies of kiwifruit have demonstrated positive results in the treatment of constipation in a range of adult populations, including healthy subjects, the elderly and patients with IBS.

− These studies suggest that daily consumption of kiwifruit may be effective for the treatment of constipation or functional bowel disorders, as well as an effective strategy to regulate the digestive system and enhance bowel movement satisfaction.

• Research on the digestive health benefits of kiwifruit is ongoing, with results of a multi-country, randomised, cross-over, controlled, clinical intervention study expected in 2016.

37

References

1. Ansell J, Butts CA, Paturi G, Eady SL, Wallace AJ, Hedderley D, Gearry RB. Kiwifruit-derived supplements increase stool frequency in healthy adults: A randomized, double-blind, placebo-controlled study. Nutr Res. 2015;35:401-8.

2. Paturi G, Butts CA, Bentley-Hewitt KL, Ansell J. Influence of green and gold kiwifruit on indices of large bowel function in healthy rats. J Food Sci. 2014;79:H1611-20.

3. Halmos EP, Power VA, Shepherd SJ, Gibson PR, Muir JG. A diet low in fodmaps reduces symptoms of irritable bowel syndrome. Gastroenterology 2014;146:67-75 e65.

4. Han KS, Balan P, Molist Gasa F, Boland M. Green kiwifruit modulates the colonic microbiota in growing pigs. Lett Appl Microbiol. 2011;52:379-85.

5. Rosendale DI, Blatchford PA, Sims IM, Parkar SG, Carnachan SM, Hedderley D, Ansell J. Characterizing kiwifruit carbohydrate utilization in vitro and its consequences for human faecal microbiota. J Proteome Res. 2012;11:5863-75.

6. O’Hara AM, Shanahan F. The gut flora as a forgotten organ. EMBO Reports. 2006;7:688-93.

7. Garcia-Lafuente A, Antolin M, Guarner F, Crespo E, Malagelada JR. Modulation of colonic barrier function by the composition of the commensal flora in the rat. Gut. 2001;48:503-7.

8. Sims IM, Monro JA. Fiber: Composition, structures, and functional properties. Adv Food Nutr Res. 2013;68:81-99.

9. Redgwell RJ, Melton LD, Brasch DJ. Cell wall dissolution in ripening kiwifruit (actinidia deliciosa): Solubilization of the pectic polymers. Plant Physiol. 1992;98:71-81.

10. Redgwell RJ, Fisher M, Kendal E, MacRae EA. Galactose loss and fruit ripening: high-molecular-weight arabinogalactans in the pectic polysaccharides of fruit cell walls. Planta. 1997;203:174–81.

11. Marlett JA, Kajs TM, Fischer MH. An unfermented gel component of psyllium seed husk promotes laxation as a lubricant in humans. Am J Clin Nutr. 2000;72:784-9.

12. Montoya CA, Rutherfurd SM, Olson TD, Purba AS, Drummond LN, Boland MJ, Moughan PJ. Actinidin from kiwifruit (Actinidia deliciosa cv. Hayward) increases the digestion and rate of gastric emptying of meat proteins in the growing pig. Br J Nutr. 2014;111:957-67.

13. Kaur L, Rutherfurd SM, Moughan PJ, Drummond L, Boland MJ. Actinidin enhances gastric protein digestion as assessed using an in vitro gastric digestion model. J Agric Food Chem. 2010;58:5068-73.

14. Kaur L, Rutherfurd SM, Moughan PJ, Drummond L, Boland MJ. Actinidin enhances protein digestion in the small intestine as assessed using an in vitro digestion model. J Agric Food Chem. 2010;58:5074-80.

15. Drummond L, Gearry RB. Kiwifruit modulation of gastrointestinal motility. Adv Food Nutr Res. 2013;68:219-32.

16. Parkar SG, Rosendale D, Paturi G, Herath TD, Stoklosinski H, Phipps JE, Hedderley D, Ansell J. In vitro utilization of gold and green kiwifruit oligosaccharides by human gut microbial populations. Plant Foods Hum Nutr. 2012;67:200-7.

17. Bentley-Hewitt KL, Blatchford PA, Parkar SG, Ansell J, Pernthaner A. Digested and fermented green kiwifruit increases human beta-defensin 1 and 2 production in vitro. Plant Foods Hum Nutr. 2012;67:208-14.

18. Blatchford P, Bentley-Hewitt KL, Stoklosinski H, McGhie T, Gearry R, Gibson G, Ansell J. In vitro characterisation of the fermentation profile and prebiotic capacity of gold-fleshed kiwifruit. Benef Microbes. 2015:1-12.

19. Molan AL, Kruger MC, and Drummond, L.N. : The ability of kiwifruit to positively modulate markers of gastrointestinal health. Proceedings of the Nutrition Society of New Zealand 2007;32: 66-71.

20. Parkar SG, Redgate EL, Wibisono R, Luo X, Koh ETH, Schrӧder R. Gut health benefits of kiwifruit pectins: Comparison with commercial functional polysaccharides. J Funct Foods. 2010;2:210-8.

21. Ansell J, Parkar S, Paturi G, Rosendale D, Blatchford P. Modification of the colonic microbiota. Adv Food Nutr Res. 2013;68:205-17.

22. Carnachan SM, Bootten TJ, Mishra S, Monro JA, Sims IM. Effects of simulated digestion in vitro on cell wall polysaccharides from kiwifruit (Actinidia spp.). Food Chemistry. 2012;133:132-9.

23. Rutherfurd SM, Montoya CA, Zou ML, Moughan PJ, Drummond LN, Boland MJ. Effect of actinidin from kiwifruit (Actinidia deliciosa cv. Hayward) on the digestion of food proteins determined in the growing rat. Food Chem. 2011;129:1681-9.

24. Montoya CA, Hindmarsh JP, Gonzalez L, Boland MJ, Moughan PJ, Rutherfurd SM. Dietary actinidin from kiwifruit (Actinidia deliciosa cv. Hayward) increases gastric digestion and the gastric emptying rate of several dietary proteins in growing rats. J Nutr. 2014;144:440-6.

25. Zespri®: Data on file.

26. Rush EC, Patel M, Plank LD, Ferguson LR. Kiwifruit promotes laxation in the elderly. Asia Pac J Clin Nutr. 2002;11:164-8.

27. Chan AO, Leung G, Tong T, Wong NY. Increasing dietary fiber intake in terms of kiwifruit improves constipation in Chinese patients. World J Gastroenterol. 2007;13:4771-5.

28. Chang CC, Lin YT, Lu YT, Liu YS, Liu JF. Kiwifruit improves bowel function in patients with irritable bowel syndrome with constipation. Asia Pac J Clin Nutr. 2010;19:451-7.

29. Cunillera O, Almeda J, Mascort JJ, Basora J, Marzo-Castillejo M and the Catalan Kiwifruit Study Group. Improvement of functional constipation with kiwifruit intake in a Mediterranean patient population: An open, non-randomised pilot study. Rev Esp Nutr Hum Diet. 2015;19:58-67.

30. Zespri®: Data on file.

31. Halmos EP, Power VA, Shepherd SJ, Gibson PR, Muir JG. A diet low in fodmaps reduces symptoms of irritable bowel syndrome. Gastroenterology 2014;146:67-75 e65.

32. Ong D, Mitchell S, Barrett J, et al. Manipulation of dietary short chain carbohydrates alters the pattern of gas production and genesis of symptoms in irritable bowel syndrome. J Gastroenterol Hepatol 2010; 25: 1366-73.

33. Barrett J, Gearry R, Muir J, et al. Dietary poorly absorbed, short-chain carbohydrates increase delivery of water and fermentable substrates to the proximal colon. Aliment Pharmacol Ther 2010; 31: 874-82.

34. Marciani L, Cox E, Hoad C, et al. Postprandial changes in small bowel water content in healthy subjects and patients with irritable bowel syndrome. Gastroenterology 2010; 138: 469-77.

35. Staudacher HM, Lomer MC, Anderson JL, et al. Fermentable carbohydrate restriction reduces luminal bifidobacteria and gastrointestinal symptoms in patients with irritable bowel syndrome. J Nutr 2012; 142: 1510-8.

36. Staudacher H, Whelan K, Irving P, Lomer M. Comparison of symptom response following advice for a diet low in fermentable carbohydrates (FODMAPs) versus standard dietary advice in patients with irritable bowel syndrome. J Hum Nutr Diet 2011; 24: 487-95.

37. De Roest R, Dobbs B, Chapman B, et al. The low FODMAP diet improves gastrointestinal symptoms in patients with irritable bowel syndrome: A prospective study. Int J Clin Pract 2013; 67: 895-903.

38. Biesiekierski J, Peters S, Newnham E, Rosella O, Muir J, Gibson P. No effects of gluten in patients with self-reported non-celiac gluten sensitivity following dietary reduction of low-fermentable, poorly-absorbed, short-chain carbohydrates. Gastroenterology 2013; 145: 320-8.

39. Monash University (2015). The Monash University Low FODMAP Diet for Apple iOS (Version 1.5.1.) [Mobile application software]. Retrieved from https://itunes.apple.com/au/app/monash-university-low-fodmap/id586149216?mt=8


Vitamin C and Health

Vit

amin

C a

nd

Hea

lth

41

Vitamin C is an Essential Vitamin that Cannot Be Synthesised by the Human Body

Vitamin C, also known as ascorbic acid or ascorbate (Figure 1), is a water-soluble vitamin that is naturally present in some foods and available as a dietary supplement. While some animals can synthesise their own vitamin C from glucose, humans do not have this ability and therefore must obtain vitamin C through the diet1. The human body can store only a certain amount of vitamin C, so it must be ingested on a daily basis1. An adequate intake of vitamin C is required for the proper development and function of many parts of the body, and has been shown to limit the risk of developing chronic diseases such as heart disease and cancer1, 2.

Vitamin C and Health

HO

HO

HO

CH2OH

C H

H

O

O

Figure 1. Chemical structure of vitamin C (ascorbic acid or ascorbate)

42

Breakout box 1: Antioxidants13, 17

Antioxidants are natural or man-made substances that may prevent or delay some types of cell damage. They do this by blocking some of the damage caused by free radicals, unstable molecules created every day during normal metabolism that damage DNA. The build-up of free radicals over time may contribute to the aging process and the development of health conditions such as cancer, heart disease, and arthritis. On-going research is examining the role of antioxidants in the prevention or delay of the development of certain cancers, cardiovascular disease, and other diseases in which oxidative stress plays a fundamental role.

Vitamin C Has an Important Role in Human Metabolic Processes

Vitamin C has important effects on the body, and contributes to:

• Normal function of the immune system Vitamin C plays an important role in immune function, and has been shown to have

immunostimulant, anti-inflammatory, antiviral and antibacterial properties3,4.

• Energy metabolism Vitamin C is required for the synthesis of carnitine, a compound that plays a critical role

in energy production, by transporting long-chain fatty acids into the cell so they can be oxidized (‘burned’) for fuel5.

• Normal psychological function, which helps to reduce tiredness and fatigue Vitamin C helps to activate a series of enzymes that improve metabolic energy levels

and different neurochemicals in the brain, therefore taking vitamin C could reduce the sensation of fatigue and increase physical and mental energy6-8.

• Tissue formation and wound healing Vitamin C is required for the biosynthesis of collagen, an essential component of

connective tissue which plays a vital role in wound healing9.

• Production of a range of enzymes Vitamin C is required as a cofactor (or “helper molecule” that assists in biochemical

reactions) for a number of different enzymes which play important roles in the maintenance of normal metabolism and cellular responses to environmental stresses10-12.

• Protection of cellular DNA, proteins and lipids Vitamin C is a powerful antioxidant and can help reduce the damage to cells and tissues

caused by the products of normal metabolism (see Breakout box 1)13. It has also been shown to regenerate other antioxidants within the body, including vitamin E14.

• Maintenance of the structure and function of the skeletal muscle Due to its role in creating collagen and protecting metabolically active cells from

oxidative stress, vitamin C can help to protect muscle tissue against damage by free radicals15,16.

43

Breakout box 2: Recommended Dietary Allowance (RDA)

The RDA is the average daily level of intake sufficient to meet the nutrient requirements of nearly all (97-98%) healthy individuals20. The RDA for vitamin C, based on its known physiological and antioxidant functions in white blood cells, is set much higher than the amount required for protection from deficiency while ensuring that there is minimal excretion in the urine20.

However, since the last RDA review which recommends 60 mg of vitamin C daily, scientists have suggested a need for elevated vitamin C consumption. A 1996 study by Levine et al., which investigated vitamin C pharmacokinetics in seven healthy men, proposed that the RDA should be increased to 200 mg daily21. Based on these newer studies, the recommended level in the US was increased from 60 mg/day to 90 mg/day for men and from 45 mg/day to 75 mg/day for women in 2000. In Australasia, the RDA remains at 45 mg/day22.

How Much Vitamin C Do We Need?

The current US recommended dietary allowance (RDA, see Breakout box 2) for vitamin C, established by the Food and Nutrition Board/National Research Council in 1980 and reconfirmed in 1989, is 60 mg daily18, 19. However, more recent research suggests that the RDA for vitamin C should be increased. Fruits and vegetables are generally regarded as the best available source of vitamin C. However, because ascorbic acid is water soluble and destroyed by heat, the vitamin C content of food may be reduced by prolonged storage and cooking20. Fortunately, most fruits and some vegetables can be consumed raw and consuming several varied servings of fruits and vegetables a day can provide more than the RDA of vitamin C.

44

One Zespri® Kiwifruit a Day Gives the Daily Requirement of Vitamin C

Zespri® kiwifruit is one of the best sources of vitamin C among fruit and vegetables (Figure 2). Zespri SunGold kiwifruit contains almost three times the amount of vitamin C found in oranges and strawberries, traditionally known as good sources of vitamin C23.

Figure 2. Graph comparing the vitamin C content of various fruits with Zespri® kiwifruit23

Zespri® Kiwifruit is Very Effective at Increasing Plasma Levels of Vitamin C

Vitamin C status is typically assessed by measuring blood plasma vitamin C levels14, 24. This is because human tissues are not always accessible for evaluation, and since blood is the vehicle for vitamin C transport, plasma concentrations are a reasonable indicator of its concentration in the body.

A recent study in New Zealand showed that regular consumption of two gold kiwifruit significantly increased plasma levels of ascorbic acid (vitamin C) in men with a normal level of vitamin C15. This effect was even greater in those with previous low levels of vitamin C15.

This study determined a comparable relative bioavailability of kiwifruit-derived vitamin C and synthetic vitamin C in non-smoking males that received either a chewable tablet (200 mg vitamin C) or the equivalent dose from kiwifruit15.

200

150

100

50

0

Apples

Orange

s

Blueb

errie

s

Stra

wberri

esPe

ars

Pom

egra

nates

Man

darin

es

Papa

yas

4.6 4.014

53.258.8

26.718.0

9.7 4.3 8.1 10.2

36.4

19.7

60.947.8

84.0

8.7

Vit

amin

C (m

g/10

0 g)

Man

goes

Melo

ns

Wat

erm

elons

Banan

as

Cranbe

rries

Grape

s

Pinea

pples

Longa

ns

Durians

Zespri S

unGold*

161.3

Zespri G

reen**

85.1 EURDA 100%

EURDA 15%


45

Kiwifruit and Vitamin C-Related Health: What is the Evidence?

Consumption of kiwifruit is associated with enhanced immune cell function

Vitamin C is thought to be essential for the function of neutrophils, cells of the immune system that defend against invading pathogens (see Breakout box 3). A recent study has demonstrated that supplementation with vitamin C-rich kiwifruit improves important neutrophil functions, which likely translates to enhanced immunity25.

EX VIVO STUDIES

In this study, young men with low vitamin C status were fed two Zespri SunGold kiwifruit daily for a period of 4 weeks25. Plasma vitamin C levels increased to >70 μmol/L within one week of supplementation (Figure 3a) and a significant increase in neutrophil vitamin C status following four weeks of kiwifruit supplementation was seen (Figure 3b).

Breakout box 3: Neutrophils and inflammation25

Neutrophils are the most common type of white blood cell and form an essential part of the innate immune system. They detect and migrate to sites of infection (a process known as chemotaxis) where they engulf and kill micro-organisms. This process, known as phagocytosis, requires oxygen and results in the secretion of chemically reactive molecules called reactive oxygen species (ROS). The release of ROS is also known as an ‘oxidative burst’.

Neutrophils in the circulation

Movement into tissues (chemotaxis)

Phagocytosis and destruction of bacteria

Bacteria

Oxidative burst

46

Figure 3 (a). Plasma vitamin C levels25

Figure 3 (b). Neutrophil vitamin C status following 4 weeks of kiwifruit supplementation25

In addition to increased plasma and neutrophil vitamin C status, a statistically significant 20% increase in neutrophil chemotaxis was observed post-intervention, demonstrating that vitamin C enhances the anti-microbial function of neutrophils (Figure 4a). Additionally, concentrations of the superoxide, a type of ROS (see Breakout box 3), increased, which likely translates into enhanced microbial killing capacity (Figure 4).

100

80

60

40

20

0

Plas

ma

vita

min

C (

µm

ol/

L)

Week 4: Supplementation with two kiwifruit/day

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47

Vitamin C is retained in parts of the body where it is most essential

A study using a Gulo mouse model investigated the effectiveness of vitamin C uptake from a kiwifruit gel (Zespri Green and Gold kiwifruit) compared to a synthetic supplement over a period of 4 weeks26. Like humans, these animals are incapable of synthesising vitamin C, but can be healthy and grow normally when the vitamin is added to the diet. After 4 weeks, mice fed with the kiwifruit gel-supplemented diet had substantially higher tissue levels of vitamin C than those mice consuming an equivalent dose of vitamin C in the drinking water (Figure 5)26. Whilst the striking results suggested a differential uptake, this has not been observed in human studies. The observed differences are believed to be related to the different set and pattern of vitamin C transporters in the mice, which normally manufacture their own vitamin C and are therefore less well equipped to absorb dietary sources.

Importantly, the authors of this study also noted that a suboptimal intake of dietary vitamin C could lead to reductions in intracellular vitamin C, particularly in the liver and kidneys. Interestingly, the brain was found to be most resilient, with approximately 50% of vitamin C remaining after 1 week and close to 10% of the initial content being detectable after 4 weeks26. These results demonstrate that vitamin C is preferentially accumulated in brain tissue, indicating a vital role for vitamin C in the brain26. The study also showed that mice with suboptimal levels of vitamin C appeared to be healthy for a prolonged period before overt signs of poor health appeared, suggesting the suboptimal levels meant they were basically “unwell”.

IN VIVO STUDIES

Figure 4. Neutrophil chemotaxis (a) and superoxide generation (b) at baseline and post-intervention25

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48

Figure 5. Tissue vitamin C concentrations in mice fed kiwifruit gel with a known vitamin C content ( ) or synthetic vitamin C supplement in drinking water ( )26

Each data point represents the mean (±SE) value for 3 to 12 animals. Reagent ascorbate (4.2 mg/d) was also delivered in a gel form to control for differences in absorption ( ).

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49

CLINICALSTUDIES

Consumption of one kiwifruit per day is sufficient to achieve ‘healthy’ plasma levels of vitamin C

To more accurately measure the contribution of kiwifruit (Zespri Gold kiwifruit) to dietary vitamin C intake, plasma vitamin C levels were measured in a group of 14 male students with low vitamin C status (average baseline plasma 38 mM)27. Participants were asked to consume half a kiwifruit per day for 4 weeks, followed by one kiwifruit per day for 6 weeks, two kiwifruit per day for 6 weeks and finally three kiwifruit per day for 4 weeks (Figure 6)27.

Figure 6. Study design27

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 Weeks

Lead-in

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Phase I Phase II (intervention) Phase III

1/2 kiwifruit/d 1 kiwifruit/d 2 kiwifruit/d 3 kiwifruit/d Washout

The results showed that consuming kiwifruit had a strong effect on plasma vitamin C levels, with increases of around 25 mM (Figures 7a and b)27. The addition of as little as half a kiwifruit per day resulted in a significant increase in plasma vitamin C, however, one kiwifruit per day was required to reach what is considered healthy levels27. At two kiwifruit per day, plasma levels approached saturation with no further increase with three per day27. This was confirmed by increased urinary output of the vitamin at two kiwifruit per day (which coincided with plasma levels reaching around 60 mM; Figure 8)27. These results confirm the pharmacokinetic data of Levine et al.21 (see Breakout box 2) and indicate that plasma vitamin C levels in humans saturate at an intake of about 200 mg/day27. This is equivalent to eating approximately two kiwifruit per day.

Lead-in phase of 4 weeks, intervention phase of 20 weeks and a washout phase of 4 weeks.

* Fasting blood samples

† 24h urine collection and total leucocyte preparations carried out when food and beverage diaries completed

50

Figure 7. (a) Daily fruit and vegetable consumption and (b) vitamin C intake by the study participants27

Data are means with standard errors represented by vertical bars. The number of participants are indicated in parentheses. * Mean value was significantly different from that at baseline (P<0.05; one-way repeated-measures ANOVA with the Fisher least significant deviation pairwise multiple comparison procedure). WO, washout.

Figure 8. Correlation of plasma vitamin C with urinary excretion of vitamin C27

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51

Kiwifruit effectively increases vitamin C levels in blood plasma and skeletal muscle

A study investigating the bioavailability of vitamin C to human skeletal muscle found that muscle is highly responsive to vitamin C intake (and hence plasma concentrations), and is likely to be prone to depletion with inadequate dietary intake15. In this study, 36 men were given either half a kiwifruit or two kiwifruits (Zespri Gold kiwifruit) per day for 6 weeks. Baseline mean muscle tissue vitamin C concentrations were ∼16 nmol/g tissue, with a range from 1.0 to 43.2 nmol/g tissue.

After 6 weeks of kiwifruit consumption, there was a ∼3.5-fold increase in mean muscle tissue vitamin C concentrations to 53 and 61 nmol/g tissue in the low- and high-dose groups, respectively15. Authors also measured vitamin C concentrations of mononuclear cells and neutrophils, which showed a significantly smaller relative uptake of vitamin C compared with muscle tissue uptake (Figure 9)15. There was no difference in muscle tissue ascorbate concentrations between the two groups, which suggested that muscle tissue vitamin C concentrations were saturated with half a kiwifruit per day15. Authors of this study suggest that daily vitamin C intake that provides plasma vitamin C concentrations ≥50 μmol/L should be consumed to maintain an optimal skeletal muscle vitamin C status15.

Figure 9. Mean ± SEM relative increases in vitamin C concentrations in peripheral blood mononuclear cells, neutrophils and skeletal muscle tissue15

Supplementation with 0.5 kiwifruit/d (n = 18; green bars) or 2 kiwifruit/d (n = 18; yellow bars) *p<0.01; **p<0.001

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52

Kiwifruit supplementation improves overall mood

A recent study in young men has shown that eating two kiwifruit (Zespri Gold kiwifruit) per day can improve a person’s overall mood6. In this study, 35 young men were supplemented with either half or two kiwifruit per day for 6 weeks. No effect on overall mood was observed in the group who ate half a kiwifruit per day; however, in the group that ate two kiwifruits per day, decreased total mood disturbance and depression trends were seen6. Further analysis of a subgroup of participants with higher than average mood disturbance indicated a significant decrease in fatigue, a concomitant increase in vigour, and a trend towards a decrease in depression following supplementation with two kiwifruit per day, but not half a kiwifruit per day (Figure 10)6.

The authors state that these improvements are likely related to the optimisation of vitamin C with the dose provided by two kiwifruit6. These results are consistent with other studies which have reported reductions in depression, fatigue and mood disturbance with vitamin C supplementation6.

Figure 10. Effect of two kiwifruit/day intervention on individual mood scores and total mood disturbance (TMD) score in the high-TMD subgroup (n=8)6

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Baseline Intervention

53

Kiwifruit consumption increases protective cellular defence

A human clinical trial found that the intake of antioxidant-rich foods could affect groups of genes associated with cellular stress defence when participants added kiwifruit to their diet28. In this study, 102 healthy male smokers were randomised to either a diet rich in various antioxidant-rich foods, a kiwifruit diet (three kiwifruits/day added to their regular diet) or a control group28.

Groups of genes involved in regulation of cellular stress defence, such as DNA repair, apoptosis and hypoxia (preventing cellular oxygen deprivation), were significantly up-regulated in participants who ate three kiwifruits per day or an antioxidant-rich diet28. Antioxidants in blood plasma, such as polyphenols and carotenoids, also increased in both groups28.

The authors of the study suggest that antioxidants found in fruits and vegetables control ROS (Reactive Oxygen Species) levels while also regulating immune defence systems (Figure 11). Antioxidant intake could therefore help prevent oxidative stress-related diseases and premature aging28.

Table 1. Summary of key outcomes from human studies investigating vitamin C from kiwifruit6, 15, 25-27

0.5 kiwifruit/day 2 kiwifruit/day

Plasma vitamin C + ++

Seminal fluid - +

Mononuclear cells + +

Neutrophils ++ ++

Muscle +++ +++

Mood score - ++

54

Figure 11. Hypothetical model suggesting how antioxidants in fruits and vegetables influence protective cellular defence systems28

Endogenous sources of ROS

Exogenous sources of ROS

Endogenous sources of ROS

Exogenous sources of ROSEndogenous sources of ROS

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Increased cellular

stress defence

Fruits/berries/vegetables

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Modulation of gene expression

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Damaged cells

Ageing/diseases/cell death

Damage to DNAmembranes, proteins etc

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ROStoo high

55

Kiwifruit consumption reduces selected upper respiratory tract infection symptoms

The common cold or influenza (flu) viruses, some of the most common causes of sickness in humans, cause symptoms of upper respiratory tract infection (URTI) such as sore throat and head congestion29. There is no specific therapy to prevent or treat the common cold, and flu vaccination is only modestly effective in older adults29. Since inadequate nutrition can contribute to increased risk and severity of URTI in the elderly, a 2012 study investigated whether kiwifruit (Zespri Gold kiwifruit), a food rich in vitamins C and E, folate, polyphenols and carotenoids, could reduce URTI symptoms29.

In this study, 32 elderly people (≥65 years) consumed the equivalent of four kiwifruit or two bananas daily for 4 weeks29. While kiwifruit did not significantly reduce the overall incidence of URTI compared with banana, the severity and duration of head congestion, and the duration of sore throat were reduced29. There was also a positive and significant influence on a number of plasma antioxidants, including vitamins C, vitamin E and lutein/zeaxanthin, and cellular damage from oxidative stress was significantly reduced. Authors conclude that eating kiwifruit may provide an important contribution to lessening the burden of respiratory infection in older people29.

Upcoming Research

The antioxidant properties of vitamin C and its role in collagen synthesis make it a vital molecule for skin health1. Vitamin C in the skin is normally transported from the bloodstream and is found at high levels in both the dermis and epidermis of human skin30. Levels of vitamin C decline with age and excessive exposures to UV light or pollutants such as cigarette smoke31,32, and therefore supplementation to increase vitamin C levels in the skin is common.

Numerous studies have demonstrated that oral supplementation with vitamin C effectively increases vitamin C levels in the skin33, 34, and recent evidence shows that combining vitamin C and vitamin E supplementation is more effective in preventing UV damage than either vitamin alone35, 36. Since Zespri® kiwifruit contains both vitamin C and vitamin E in relatively high levels, investigations into the role of kiwifruit supplementation in improving skin health and combatting signs of ageing are currently in planning stages.

56

Conclusions

• Vitamin C is an essential vitamin that cannot be synthesised by the human body, and therefore must be obtained through the diet.

• An adequate intake of vitamin C is required for the activation of numerous enzymatic reactions, various metabolic processes and the supply of antioxidants which protect against oxidative stress; deficiencies in vitamin C disrupt pathways known to cause chronic diseases, such as heart disease and cancer.

• Vitamin C plays an important role in both innate and adaptive immune system function, and is found in high concentrations in immune cells.

• Vitamin C levels in tissues are rapidly depleted, and since the human body can store only a certain amount of vitamin C, it must be ingested on a daily basis.

• Kiwifruit is a rich source of vitamin C and has been shown to be a significantly better at replenishing depleted vitamin C tissue levels compared with vitamin C supplements37; just one Zespri kiwifruit a day contains the daily requirement of vitamin C.

57

References

1. World Health Organization. Vitamin and mineral requirements in human nutrition : report of a joint FAO/WHO expert consultation, Bangkok, Thailand, 21–30 September 1998. 2004.

2. Vissers MC, Carr AC, Pullar JM, Bozonet SM. The bioavailability of vitamin C from kiwifruit. Adv Food Nutr Res. 2013;68:125-47.

3. Bergsten P, Amitai G, Kehrl J, Dhariwal KR, Klein HG, Levine M. Millimolar concentrations of ascorbic acid in purified human mononuclear leukocytes. Depletion and reaccumulation. J Biol Chem. 1990;265:2584-7.

4. Washko PW, Wang Y, Levine M. Ascorbic acid recycling in human neutrophils. J Biol Chem. J Biol Chem. 1993;268:15531-5.

5. Huskisson E, Maggini S, Ruf M. The role of vitamins and minerals in energy metabolism an wellbeing. J Int Med Res. 2007;35:277-89.

6. Carr AC, Bozonet SM, Pullar JM, Vissers MC. Mood improvement in young adult males following supplementation with gold kiwifruit, a high-vitamin C food. J Nutr Sci. 2013;2:e24.

7. Rebouche CJ. Ascorbic acid and carnitine biosynthesis. Am J Clin Nutr. 1991;54(6 Suppl):S1147-S52.

8. Kinsman RA, Hood J. Some behavioral effects of ascorbic acid deficiency. Am J Clin Nutr. 1971;24:455-64.

9. Moores J. Vitamin C: a wound healing perspective. Br J Community Nurs. 2013(6 Suppl):S8-11.

10. Englard S, Seifter S. The biochemical functions of ascorbic acid. Annu Rev Nutr. 1986;6:365-406.

11. Padayatty SJ, Levine M. Vitamin C: the known, the unknown, and Goldilocks. Oral Dis. 2016 [Epub ahead of print]

12. Rumsey SC, Levine M. Absorption, transport, and disposition of ascorbic acid in humans. J Nutr Biochem 1998;9:116-130.

13. Ginter E, Simko V, Panakova V. Antioxidants in health and disease. Bratisl Lek Listy. 2014;115:603-6.

14. Jacob RA, Sotoudeh G. Vitamin C function and status in chronic disease. Nutr Clin Care 2002;5:66-74.

15. Carr AC, Bozonet SM, Pullar JM, Simcock JW, Vissers MC. Human skeletal muscle ascorbate is highly responsive to changes in vitamin C intake and plasma concentrations. Am J Clin Nutr. 2013;97:800-7.

16. Frei B, England L, Ames BN. Ascorbate is an outstanding antioxidant in human blood plasma. Proc Natl Acad Sci USA. 1989;86:6377-81.

17. National Institutes of Health. Antioxidants and Health: An Introduction. 2015; Available from: https://nccih.nih.gov/health/antioxidants/introduction.htm [cited 05 January 2015]

18. FNB/NRC. Recommended Dietary Allowances. Tenth Revised Edition; Food and Nutrition Board. 1989: Washington, DC.

19. FNB/NRC. Recommended Dietary Allowances. Ninth Revised Edition; Food and Nutrition Board. 1980: Washington, DC.

20. Institute of Medicine. Dietary Reference Intakes for Vitamin C, Vitamin E, Selenium, and Carotenoidsexternal link disclaimer. 2000: Washington, DC.

21. Levine M, Conry-Cantilena C, Wang Y, Welch RW, Washko PW, Dhariwal KR, Park JB, Lazarev A, Graumlich JF, King J, Cantilena LR. Vitamin C pharmacokinetics in healthy volunteers: evidence for a recommended dietary allowance. Proc Natl Acad Sci USA. 1996;93:3704-9.

22. Boland M, Moughan PJ. Advances in Food And Nutrition Research. Nutritional Benefits of Kiwifruit. 2013, Waltham, MA: Elsevier Inc.

23. USDA. USDA national nutrient database for standard reference (Release 28). 2015.

24. Bates CJ. Bioavailability of vitamin C. Eur J Clin Nutr. 1997;51(Suppl 1):S28-33.

25. Bozonet SM, Carr AC, Pullar JM, Vissers MC. Enhanced human neutrophil vitamin C status, chemotaxis and oxidant generation following dietary supplementation with vitamin C-rich SunGold kiwifruit. Nutrients. 2015;7:2574-88.

26. Vissers MC, Bozonet SM, Pearson JF, Braithwaite LJ. Dietary ascorbate intake affects steady state tissue concentrations in vitamin C-deficient mice: tissue deficiency after suboptimal intake and superior bioavailability from a food source (kiwifruit). Am J Clin Nutr. 2011;93:292-301.

27. Carr AC, Pullar JM, Moran S, Vissers MC. Bioavailability of vitamin C from kiwifruit in non-smoking males: determination of ‘healthy’ and ‘optimal’ intakes. J Nutr Sci. 2012;1:e14.

28. Bøhn SK, Myhrstad MC, Thoresen M, Holden M, Karlsen A, Tunheim SH, Erlund I, Svendsen M, Seljeflot I, Moskaug JO, Duttaroy AK, Laake P, Arnesen H, Tonstad S, Collins A, Drevon CA, Blomhoff R. Blood cell gene expression associated with cellular stress defense is modulated by antioxidant-rich food in a randomised controlled clinical trial of male smokers. BMC Med. 2010;8:54.

29. Hunter DC, Skinner MA, Wolber FM, Booth CL, Loh JM, Wohlers M, Stevenson LM, Kruger MC. Consumption of gold kiwifruit reduces severity and duration of selected upper respiratory tract infection symptoms and increases plasma vitamin C concentration in healthy older adults. Br J Nutr. 2012;108:1235-45.

30. Shindo Y, Witt E, Han D, Epstein W, Packer L. Enzymic and non-enzymic antioxidants in epidermis and dermis of human skin. J Invest Dermatol. 1994;102:122-4.

31. Podda M, Traber MG, Weber C, Yan LJ, Packer L. UV-irradiation depletes antioxidants and causes oxidative damage in a model of human skin. Free Radic Biol Med. 1998;24:55-65.

32. Rhie G, Shin MH, Seo JY, Choi WW, Cho KH, Kim KH, Park KC, Eun HC, Chung JH. Aging- and photoaging-dependent changes of enzymic and nonenzymic antioxidants in the epidermis and dermis of human skin in vivo. J Invest Dermatol. 2001;117:1212-7.

33. Fuchs J, Kern H. Modulation of UV-light-induced skin inflammation by D-alpha-tocopherol and L-ascorbic acid: a clinical study using solar simulated radiation. Free Radic Biol Med. 1998;25:1006-12.

34. McArdle F, Rhodes LE, Parslew R, Jack CI, Friedmann PS, Jackson MJ. UVR-induced oxidative stress in human skin in vivo: effects of oral vitamin C supplementation. Free Radic Biol Med. 2002;33:1355-62.

35. Eberlein-König B, Placzek M, Przybilla B. Protective effect against sunburn of combined systemic ascorbic acid (vitamin C) and d-alpha-tocopherol (vitamin E). J Am Acad Dermatol. 1998;38:45-8.

36. Placzek M, Gaube S, Kerkmann U, Gilbertz KP, Herzinger T, Haen E, Przybilla B. Ultraviolet B-induced DNA damage in human epidermis is modified by the antioxidants ascorbic acid and D-alpha-tocopherol. J Invest Dermatol. 2005;124:304-7.

37. Stonehouse W, Gammon CS, Beck KL, Conlon CA, von Hurst PR, Kruger R. Kiwifruit: our daily prescription for health. Can J Physiol Pharmacol. 2013;91:442-7.


Metabolic Health

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61

Metabolic Health

Kiwifruit Has a Low Glycaemic Index

The glycaemic index (GI) indicates the amount of glucose that is released during digestion from carbohydrates into the blood system within about two hours of a meal. High GI foods are rapidly digested and absorbed, and result in rapid, marked rise in plasma glucose levels, whereas the same amount of carbohydrate in low GI foods are more slowly digested and absorbed, resulting in a gradual rise in plasma glucose response and insulin levels1. Foods are classified as either: • High GI (GI >70) • Medium GI (GI 55–70) • Low GI (GI <55)

Approximately 80% of the dry weight of kiwifruit consists of available carbohydrate, including glucose, fructose and sucrose at a ratio of about 2:2:1 (Figure 1)2. Of these sugars, glucose has a GI of 100% (reference value), fructose 19% and sucrose 68%2. The GI of kiwifruit reflects the proportion of sugars in the fruit, and any other factors that might reduce the rate at which the sugars are absorbed. Zespri Green kiwifruit has a GI of 39 and Zespri SunGold kiwifruit has a GI of 383. This puts kiwifruit in the GI category of ‘low’ (GI <55) (Figure 2).

Glucose Fructose Sucrose

Figure 1. Types of carbohydrates in kiwifruit2

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62

Figure 2. Relative glycaemic impact and GI of kiwifruit compared to other common foods2

Kiwifruit (100 g)

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Kiwifruit Modulates Carbohydrate Digestion and Absorption

The remaining 20% of the dry weight of kiwifruit consists of protein (10%) and primary cell walls or fibre (10%)2. The cell wall component of kiwifruit is undigested in the stomach and small intestine, and therefore increases in relative concentration in the gut lumen2. During digestion, the fibre in kiwifruit swells to four times its original volume, which reduces the rate of glucose diffusion by about 40% and profoundly reduces digesta mixing, the process which enables the transfer of sugars from the intestinal lumen to the gut wall2. This causes a delay in carbohydrate digestion and absorption and may explain why the measured GI of whole kiwifruit (GI = 39) is much lower than would be calculated from the GI of the sugars alone (GI = 60).

The Glycaemic Response Per Kiwifruit is Low

The glycaemic response to a fruit depends not only on GI, but also on the amount of carbohydrate consumed in the fruit. As kiwifruit contains only about 12% available carbohydrate, and has a low GI, a 100 g kiwifruit is equivalent to about 5 g (1 teaspoon) of glucose in its glycaemic effect. The impact kiwifruit produces on plasma glucose levels is low enough for the fruit to be suitable in managing diets for people with a reduced tolerance to glucose, and suggests that kiwifruit may be beneficial in protecting against disorders related to absorption rate, such as the postprandial blood glucose excursion2.

63

Kiwifruit Can Help Manage Blood Sugar Levels in People With Diabetes

Diabetes mellitus is an alteration of the body’s tolerance to glucose, and has various causes4. About 382 million people in the world suffer from diabetes (between 5% and 6% of the population); in addition, there is a significant proportion of the population who, although not meeting all the criteria for diabetes, have challenges around managing their blood sugar levels5.

Diabetes leads to poor absorption of glucose from the blood by the body’s tissues, so that levels may build up in the blood. High blood glucose concentrations may lead to multiple complications4. Patients with diabetes require an adequately distributed intake of carbohydrates consumed in moderate quantity to prevent hyperglycaemic episodes, and carbohydrates with the lowest GI are the most appropriate4. With a low GI of 38–39, combined with a modest content of carbohydrate, and a fibre component that reduces the rate of absorption, kiwifruit is an excellent option for people with diabetes trying to manage their blood sugar levels.

Kiwifruit Affects Gut Microbiota

There is growing evidence that consumption of kiwifruit beneficially modulates the colonic microbiota (more information can be found in the Digestive Health section of this Scientific Pack)6-14. These colonic microbiota have recently been identified as a new potential factor in obesity-related disorders, including type 2 diabetes15. Growing evidence in clinical studies suggests that the colonic microbiota are altered in obese people, and it has been proposed that these alterations may lead to chronic low-level inflammation, insulin resistance and onset of type 2 diabetes16.

Kiwifruit and Metabolic Health: In Vitro and In Vivo Studies

Kiwifruit reduces the rate of glucose diffusion

An in vitro study investigating the physicochemical properties of green and gold kiwifruit found that the undigested soluble and insoluble fibre in the kiwifruit cell walls was able to reduce the rate of processes involved in the glycaemic response17. In this study, kiwifruit flesh was digested under gastric and gastroileal conditions in vitro. The digested kiwifruit pulp of both green and gold varieties, which contained soluble and insoluble undigested polymer fractions, was found to swell to four times the volume of the original fruit and interact with other foods (Figure 3). This decreased the rate of glucose diffusion by over 40% and the rate of mixing by over 40%. Furthermore, in the presence of soluble fibre, the physical interaction of the cell wall remnants and long hydrocolloid molecules was found to increase viscosity and further decreased mixing. The authors concluded that the additive effects of decreased mixing and decreased diffusion are likely to reduce the glycaemic response, and may explain why the GI of the sugars consumed in kiwifruit is so much less than the GI of the same sugars consumed alone.

IN VITRO STUDIES

64

Kiwifruit slows intestinal processes

In a series of in vitro studies, Monro et al.18 found that when kiwifruit flesh had been digested in vitro, the non-digested dietary fibre remnants would surround and extensively interact with other foods in the limited volume of the gut. These non-digested dietary fibre remnants of pre-digested kiwifruit flesh substantially retarded digestion, sugar diffusion and mixing of intestinal contents, all of them processes important to the glycaemic response.

Figure 3. Volume of kiwifruit pulp before and after digestion

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Swollen volume of digestion-resistant remnants of kiwifruit from green and gold kiwifruit relative to the volume of the pulp before digestion. The digestion-resistant remnants had been allowed to settle overnight in a measuring cylinder.

Green kiwifruit Gold kiwifruit

65

CLINICALSTUDIES

Kiwifruit reduces the glycaemic impact of high carbohydrate foods and enhances nutrient absorption

In a human intervention study conducted by Monro et al.18, the glycaemic impact of kiwifruit was found to be relatively low, with 100 g of kiwifruit exerting approximately the same effect on blood sugar levels as only 6 g of glucose. The authors conclude that this low in vivo glycaemic impact could be partly attributed to the carbohydrate in kiwifruit being fruit sugars, and partly to the non-digested kiwifruit remnants reducing the rate of intestinal processes such as digestion, sugar diffusion and mixing of intestinal contents18.

Researchers also found that partially substituting high glycaemic foods – such as those based on cereal starch – with kiwifruit improved uptake of nutrients, including vitamin C, and reduced the glycaemic response18. Interestingly, this glycaemic benefit was greatest when kiwifruit were consumed approximately 30 minutes before consumption of a cereal meal, substantially lowering both the amplitude of the response (the “spike”) compared with consuming the two foods together, while inducing a lower total response (area under the curve) compared with an equal carbohydrate amount of the non-substituted food. Authors conclude that partial substitution of starch-based staples, such as cereals, potatoes and rice, with kiwifruit is an effective dietary strategy to simultaneously reduce exposure to glycaemia while increasing the amount of nutrients consumed2.

Upcoming Research

A cross-sectional pilot study is currently underway to investigate the relationships between gut microbiota composition and diet in people with metabolic disorders19. The objectives of the study are to:

• Define gut microbiota composition associated with normal glucose tolerance, pre-diabetes and type 2 diabetes.

• Identify dietary associations with gut microbiota composition with particular emphasis on fruit and vegetable intake.

Additionally, researchers plan to investigate the feasibility of an intervention study with kiwi-fruit to favourably alter gut microbiota composition, and therefore impact glucose tolerance.

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Conclusions

• Zespri Green and Zespri SunGold kiwifruit have a low glycaemic index of 39 and 38, respectively, and deliver a modest amount of carbohydrate per fruit, resulting in a moderate rise in plasma glucose response and insulin levels.

• The fibre in kiwifruit increases in volume in the small intestine where it reduces digesta mixing, causing a delay in carbohydrate digestion and absorption, resulting in a low glycaemic potency (6.6 GGE/100 g).

− These properties make kiwifruit an excellent option for people with diabetes, and assist with management of blood sugar levels by carbohydrate exchange.

• Consumption of kiwifruit beneficially modulates colonic microbiota, which have been shown to be linked to chronic low-level inflammation, insulin resistance and onset of type 2 diabetes in obese people.

• Partial substitution of starch-based staple foods with kiwifruit is an effective dietary strategy to simultaneously improve glucose homeostasis and intake of some nutrients.

− Consuming a kiwifruit with breakfast could therefore be an effective and healthy way to reduce the glycaemic effect of high carbohydrate breakfast cereals, such as cornflakes.

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References

1. Brand-Miller JC, Stockmann K, Atkinson F, Petocz P, Denyer G. Glycemic index, postprandial glycemia, and the shape of the curve in healthy subjects: Analysis of a database of more than 1,000 foods. Am J Clin Nutr. 2009;89:97-105.

2. Monro JA. Kiwifruit, carbohydrate availability, and the glycemic response. Adv Food Nutr Res. 2013;68:257-71.

3. Boland M, Moughan PJ. Advances in food and nutrition research. Nutritional benefits of kiwifruit. Waltham, MA, Elsevier Inc, 2013.

4. Piero MN, Nzaro GM, Njagi JM. Diabetes mellitus – a devastating metabolic disorder. Asian Journal of Biomedical and Pharmaceutical Sciences 2014;04:1-7.

5. International Diabetes Federation (IDF). IDF Diabetes Atlas, 6th edition. Brussels, Belgium: 2013.

6. Parkar SG, Rosendale D, Paturi G, Herath TD, Stoklosinski H, Phipps JE, Hedderley D, Ansell J. In vitro utilization of gold and green kiwifruit oligosaccharides by human gut microbial populations. Plant Foods Hum Nutr. 2012;67:200-7.

7. Bentley-Hewitt KL, Blatchford PA, Parkar SG, Ansell J, Pernthaner A. Digested and fermented green kiwifruit increases human beta-defensin 1 and 2 production in vitro. Plant Foods Hum Nutr. 2012;67:208-14.

8. Blatchford P, Bentley-Hewitt KL, Stoklosinski H, McGhie T, Gearry R, Gibson G, Ansell J. In vitro characterisation of the fermentation profile and prebiotic capacity of gold-fleshed kiwifruit. Benef Microbes. 2015:1-12.

9. Molan AL, Kruger MC, Drummond LN. The ability of kiwifruit to positively modulate markers of gastrointestinal health. Proceedings of the Nutrition Society of New Zealand. 2007;32:66-71.

10. Parkar SG, Redgate EL, Wibisono R, Luo X, Koh ETH, Schrӧder R. Gut health benefits of kiwifruit pectins: Comparison with commercial functional polysaccharides. Journal of Functional Foods. 2010;2:210-18.

11. Ansell J, Parkar S, Paturi G, Rosendale D, Blatchford P. Modification of the colonic microbiota. Adv Food Nutr Res. 2013;68:205-17.

12. Carnachan SM, Bootten TJ, Mishra S, Monro JA, Sims IM. Effects of simulated digestion in vitro on cell wall polysaccharides from kiwifruit (Actinidia spp.). Food Chemistry. 2013;133:132-9.

13. Rosendale DI, Blatchford PA, Sims IM, Parkar SG, Carnachan SM, Hedderley D, Ansell J. Characterizing kiwifruit carbohydrate utilization in vitro and its consequences for human faecal microbiota. J Proteome Res. 2012;11:5863-75.

14. Blatchford P. Kiwifruit-driven microbiota, metabolites and implications for human health. Abstract presented at: 1st International Symposium on Kiwifruit and Health; 2016 Apr 12-14; Tauranga, New Zealand.

15. Egshatyan L, Kashtanova D, Popenko A, Tkacheva O, Tyakht A, Alexeev D, Karamnova N, Kostryukova E, Babenko V, Vakhitova M, Boytsov S. Gut microbiota and diet in patients with different glucose tolerance. Endocrine Connections. 2016;5:1-9.

16. Zhang Y, Zhang H. Microbiota associated with type 2 diabetes and its related complications. Food Science and Human Wellness. 2013;2:167–72.

17. Mishra S, Monro J. Kiwifruit remnants from digestion in vitro have functional attributes of potential importance to health. Food Chem. 2012;135:2188-94.

18. Monro J. Kiwifruit – a double agent for glycaemic control and nutrient enhancement. Abstract presentation at: 1st International Symposium on Kiwifruit and Health; 2016 Apr 12-14; Tauranga, New Zealand.

19. Wilson R. Diet, microbiota and metabolic health. Abstract presentation at: 1st International Symposium on Kiwifruit and Health; 2016 Apr 12-14; Tauranga, New Zealand.

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Dr Juliet AnsellDPhil (Oxon):Innovation Leader Health & Nutrition at Zespri International Ltd

Email: [email protected]: +64 7 572 7798

Dr Véronique ParmentierBSc, PhD:Global Health Marketing Manager at Zespri International Ltd

Email: [email protected]: +32 3 201 08 44

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