lecture 2 dietary carbohydrates & proteins

Nutrition and HealthLecture 2

Dietary Carbohydrates & Proteins

Ain Shams University, Faculty of MedicineDepartment of Medical Biochemistry & Molecular Biology

Prof. Reem M. SallamDr. Asmaa mohamed

Department of Medical Biochemistry & Molecular Biology

Faculty of Medicine, Ain Shams University

1.Determine the quality of proteins and methods to improve it

2.Define the nitrogen balance (zero, positive, negative)3.Identify protein energy malnutrition and its types4.Define different classes of dietary lipids5.Determine the metabolic effects of different dietary

lipids in human health and disease6.Determine the harmful effects of essential fatty acids

deficiency

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Quality of proteins

It is a measure of its ability to provide the essential amino acids (AAs) required for

tissue maintenance.

Protein Digestibility-Corrected Amino Acid Score (PDCAAS):

The highest -quality dietary protein has

PDCAAS of 1

Used to balance the intakes of poorer-

quality proteins with high-quality dietary

proteins.

Digestibility of the protein.

Essential AA content of protein

Standard used to evaluate protein quality Based on:

Quality of dietary proteins according to their sources

Proteins from animal sources

High quality proteins o eg: egg, milk, beef, poultry, fish

Contain all the essential AA in proportions similar to those required

for synthesis of human tissue proteins

Gelatin ( animal collagen ) exception of an animal protein that has a low

biologic value as it lacks several essential AA:. Gelatin’s PDCAAS =

0.08)

Proteins from plant sources

lower quality (relative to animal proteins)

eg: Whole wheat bread, kidney beans, soybean protein

Exception of a plant protein that has a high biologic value as it lacks

several essential AA: Soybean protein (its PDCAAS = 1)

What is protein complementation?

Combining two incomplete proteins that have complementary amino acid deficiencies : a mixture

with a higher biologic value.

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Rice

wheat

• no lysine

• rich methionine

Kidney beans

• rich lysine

• no methionine

high biological value

Protein complementation

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Combining proteins from different plant sources

• Nutritional value equivalent to animal protein

Combining animal proteins with plant proteins

What is the amount of nitrogen in protein?.

On average, there is 1 g of nitrogen in 6.25 g protein

Nitrogen balance

1-Nitrogen consumed = nitrogen excreted Nitrogen is excreted in urine (mainly), sweat & feces.- Normally healthy adults are in nitrogen balance

2- Positive nitrogen balance Nitrogen intake > nitrogen excretion In situations when:• tissue growth occurs, e.g. children, pregnancy,

• during recovery from an emaciating illness.

3- Negative nitrogen balanceNitrogen loss > nitrogen intake:• Inadequate dietary protein , Lack of an essential amino acid• during physiologic stresses (e.g. trauma, burns, illness, or

surgery)

RDA for proteins

Infants 2 g/kg/day (To support growth) .

Pregnant or lactating women

up to 30 g/day in addition to their basal requirements

Adults 0.8 g/kg of body weight (e.g. ~56g of protein for a 70-kg individual)

~1 g/kg of body weight (strenuous exercise on a regular basis; to maintain muscle mass)

Athletes

- Variable with the protein’s biologic value: - The greater the proportion of animal protein in the diet, the less protein is required.

In kidney disease: protein restriction is recommended (nitrogen is excreted mainly in the urine as urinary urea nitrogen)

In burns: increased protein intake is recommended.

Disease stated influence protein needs

RDA for proteins

Protein-energy (calorie) malnutrition (PEM) = Protein-energy undernutrition (PEU)

It is a spectrum of degrees of

malnutrition

Two extreme forms of PEM:

Kwashiorkor Marasmus

Both cause reduced ability to resist

infection (due to depressed immune

system) and Death from secondary infection

What are the Causes of Protein-energy malnutrition (PEM)?

In developed countries:

• Medical conditions that ↓ appetite or alter

how nutrients are digested or absorbed

• Hospitalized patients with major trauma or infections

(they may require intravenous

“parenteral” or tube-based

“enteral” nutrients’ administration)

• Malnourished children or elderly

In developing countries:

The main cause is Inadequate intake

of protein &/or calories

Protein-energy (calorie) malnutrition (PEM)Kwashiorkor Marasmus

Etiology - Protein deprivation is relatively > the reduction in total calories.- Protein deprivation →

↓ synthesis of visceral protein. - In developing countries in children after weaning at ~ 1 year of age (their diet consists predominantly ofcarbohydrates)

- Calorie deprivation is relatively > the reduction in protein.

- In children < 1 year (when breast milk is supplemented (or replaced) with watery gruels of cereals deficient in protein and calories)

Kwashiorkor Marasmus

Clinical picture

1. Stunted growth 2. Edema (due todecreased plasma [albumin]) 3. Skin lesions4. Depigmented hair 5. Anorexia 6. Enlarged fatty liver

1. Arrested growth2. Extreme muscle wasting 3. Loss of subcutaneous fat (emaciation) 4. Weakness 5. Anemia 6. NO EDEMA

Weight for age (% expected):

60-80% < 60%

Weight for height:

Normal or decreased Markedly decreased

Muscle and fat content

Decreased Markedly decreased

Protein-energy (calorie) malnutrition (PEM)

Dietary Fats

1- Triacylglycerols (TAGs) (quantitatively the most important class of dietary fats)

2- Cholesterol: is found only in animal products, such as: - Liver and organ meat - Meat - egg yolk

3- Others, e.g. phospholipids

Double bound

Presence or absence of

double bonds

Number and location of

double bonds

cis/trans configuration

of double bonds

Dietary Fats

Fatty acids (FAs) have different biologic properties and are determined by:

Functions of fat in our body:

Energy source (providing more energy than carbohydrates and proteins)

Help to protect vital organs and joints Insulate the body

Carriers for fat soluble vitamins

Cholesterol is the precursor for the synthesis of various steroid hormones and vitamin D in the body.

Other specialized functions

Fats and diseases:

increased risk for CHD

decreased risk for CHD.

Dyslipidemia (abnormal levels of plasma lipids)

Fats and diseases:

The effect of dietary cholesterol on plasma cholesterol level is <important than the amount and types of fatty acids consumed.

↑saturated fat in the diet ↑ the blood levels of total& LDL-

cholesterol → ↑CHD.

Dietary cholesterol has little influence

on plasma cholesterol level:

Mediterranean diet

It is a diet rich in:

Monounsaturated fatty acids (MUFA) (olive oil)

Polyunsaturated fatty acids (PUFA) (from fish oils, plant oils, and some nuts)

It contains seasonally fresh food (fruits and vegetables)

This diet is low in saturated fat.

Low in red meat

Mediterranean diet

↓coronary heart disease (CHD).

↑plasma HDL-C

↓TAG

↓ Total C

&LDL-C

Essential fatty Acids

Fatty acids that must be supplied in food as they cannot be synthesized in our bodies.

Linoleic acid 18:2(9,12) & α Linolenic acid 18:3 (9,12,15), are required for fluidity of membrane structure and synthesis of eicosanoids.

Deficiency of essential fatty acids is characterized by scaly dermatitis, hair loss, and poor wound healing

Components of dietary fat

1-Trans fatty acids

• Do not occur naturally in plants.

• Occur in small amounts in animal food

• Formed during the hydrogenation of liquid vegetable oils,

Present in:

• Margarine

• Commercial baked goods (cookies & cakes)

• Most deep-fried foods

Trans fatty acids

↑ the risk of CHD

↓ HDL

↑ LDL

Chemically classified as unsaturated FAs, but

behave more like saturated FAs.

Saturated Fatty acids

Examples: stearic and palmitic acids

TAG composed primarily of saturated fatty acids Solid at room temp

Present in Meat (beef, lamb, pork, chicken, shell fish) Milk & dairy products as cheese and butter. Some vegetable oils as coconut & palm oils. Chocolate

Saturated Fatty acids

↑ incidence of CHD, may predispose to prostate, colon cancer

little effects on

HD

↑ LDL

↑Total cholesterol

Mono-unsaturated Fatty acids

• Present in Olive Oil Example: Oleic acid 18:1(9)TAG composed primarily of FA with one double bond.

↓ incidence of CHD

↑HDL

↓ LDL

↓ Total Cholesterol

Poly-unsaturated Fatty acids

ω-6 PUFAs e.g. linoleic acid 18:2(9,12)

ω-3 PUFAs e.g. α-linolenic acid 18:3 (9,12,15

ω-6 PUFAs

TAG composed primarily of long-chain FA, with the 1st double bond beginning at the 6th carbon atom (when counting from the methyl end).

Present in Nuts, avocados, soybeans

Various oils (including sunflower, and corn oil

ω-6 PUFAs


PG LT

↓ HDL

↓ TotalC & LDL

CProvide arachidonic acid precursor of Prostaglandin PG, Leukotrins

TAG composed primarily of long-chain FA, with the 1st double bond beginning at the 3rd carbon atom (when counting from the methyl end

Present in• Plant oils e.g. flaxseed or canola oils. • Some nuts (walnuts) • Fish oil (docosahexaenoic acid (DHA) &

eicosapentaenoic acid (EPA).

Dieticians recommend 2 fatty fish meals/week. In infant milk formulas to promote brain

development

ω-3 PUFAs


↓ risk of sudden cardiac death.

Little effect on

LDL or HDL


↓ risk of sudden cardiac death.

Suppress cardiac arrhythmias,

↓TAG

↓Tendency for

thrombosis

Lower blood

pressure

Anti-inflamm

atory

ω-3 PUFAs

Effects of dietary fats

Summary• The quality of a dietary protein is a measure of its ability to

provide the essential AA required for tissue maintenance.

• Animal proteins have a higher-quality than plant proteins, in general.

• Protein complementation: combination of proteins from different plant sources to result in improving the nutritional value

• Positive nitrogen balance: nitrogen intake > nitrogen excretion (due to tissue growth as in childhood & pregnancy, or during recovery from an emaciating illness)

• Negative nitrogen balance: nitrogen excretion > nitrogen intake (with inadequate dietary protein, lack of an essential AA, or during physiologic stresses such as trauma, burns, illness, or surgery).

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• Elevated levels of cholesterol or LDL cholesterol result in increased risk for CVD.

• Elevated levels of HDL cholesterol is associated with a decreased risk for heart disease.

• Dietary or drug treatment of hyper-cholesterolemia is effective in decreasing LDL, increasing HDL, and reducing the risk for CVD.

• Consumption of saturated fats is strongly associated with high levels of total plasma and LDL cholesterol.

• When substituted for saturated fatty acids in the diet, MUFA lower both total plasma and LDL cholesterol, and increase HDL.

• Consumption of fats containing ω-6 PUFA lowers plasma LDL, but HDL, which protect against coronary heart disease, are also lowered.

• Dietary ω-3 PUFA suppress cardiac arrhythmias and reduce serum TAG, decrease the tendency for thrombosis, and substantially reduce the risk of CVD

3/23/2021

Summary

lecture 2 dietary carbohydrates & proteins

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