Chapter 1: What you eat and why?

Objectives

Upon completion of this chapter, the student will be able to:• define the key terms used in this section. • perform some simple nutritional calculations.• list the major characteristics of the North American diet and the food

habits that often need improvement.• describe how various factors affect our food habits: • list various attributes of a healthful lifestyle that also are consistent

with Healthy People 2010 goals.• identify diet and lifestyle factors that contribute to the 10 leading

causes of death in North America.• understand the basics of the scientific method as it is used in

developing hypotheses and theories in the field of nutrition.• identify reliable sources of nutrition information.

Introduction

• During your life time:– 70,000 meals– 60 tons of food– We spend 13 – 15 years eating

What is nutrition ?

• “the science of food, the nutrients and the substances therein, their action, interaction, and balance in relation to health and disease, and the process by which the organism ingests, absorbs, transport, utilizes, and excretes food substances”----The Council on Food and Nutrition of the American Medical Association

Nutrition is

Nutrients come from food

• These are the nourishing substances we obtain from food.– Vital for growth and provide energy.– Provides building blocks– Maintain body cells– Essential nutrients

• Lead to a decline in health if omitted from diet.• Good health may be restored if nutrient is added

back to diet.• A specific biological function must be identified.

Why study nutrition?

• Link between nutrition and health.

• Poor nutrition in young predisposes to diseases in later life.

• Poor diet and sedentary lifestyle – Risk factors for chronic

diseases– Disease of the heart (31% of

all deaths)– Cancer (23%)– Cerebrovascular disease

(~5%)– Diabetes (3%)

Total = ~2/3 of all deaths

Nutrition important in disease prevention

• Poor diet + sedentary life style contribute to 300,000 deaths in U.S. each yr.

• Many diseases are preventable - “Affliction of affluence” • Excess nutrition and obesity – second leading cause of

preventable death in U.S. (Smoking # 1)• Inactivity• Age fast or age slowly - your choice.

In the 5th century B.C Hippocrates said “ Let food be your medicine and medicine be your food”

The six classes of nutrients

• Carbohydrates

• Lipids– Fats and oils

• Proteins

• Vitamins

• Minerals

• Water

Functional categories of nutrients

1. Energy-yielding nutrients (kcals)– CHO, fats and proteins

2. Nutrients important for growth, development, and maintenance.

– Proteins, lipids, vitamins, minerals & water

3. Nutrients that keep body running smoothly.

– Proteins, lipids, vitamins, minerals & water

NOTE OVERLAP HERE – Lets take a closer look at each

Carbohydrates

• Composed of C, H, O• Provide a major source of fuel

for the body.• Basic unit is glucose • Simple and Complex CHO

– Monosaccharides– Disaccharides– Polysaccharides

• Energy yielding (4 kcal /gm).• When glucose deficient we can

make it from other sources.• Dietary fiber cannot be broken

down by human enzymes - feces

Lipids

• Composed of C, H and few O• Basic unit is fatty acid.• Not soluble in water. • Triglyceride is the major form of

lipid in body and food • Fats and oils

– Fats are solid and oils liquid at RT

• Monounsaturated Fatty Acids• Polyunsaturated Fatty Acids

– Some are essential nutrients

• Saturated Fatty Acids• Essential Fatty Acids• Energy yielding (9 kcal /gm)

Proteins

• Composed of C, O, H, N• Basic unit is amino acid• Makes up bones,

muscles, other tissues• (9) Essential amino acid • (11) Nonessential amino

acid.• Energy yielding (4 kcal

/gm) – though NOT major purpose.

• Most diets in U.S. contain more than enough protein.

Vitamins

• Fat soluble (4) or water soluble (9)• Composed of various elements -

organic• Vital to life – allow chemical

reactions to proceed.• Needed in tiny amounts.• Cooking loss (particularly of

water-soluble)• Fat soluble (more likely to

accumulate)• Water soluble• Yields no energy• Allow chemical reactions to

proceed.

Minerals

• Simple inorganic substances• Needed in tiny amounts• Not destroyed in cooking but can be lost in

the cooking process.• Trace minerals (<100mg/day)• Major minerals • Yields no energy.• Important in skeletal and other systems.

Water

• Often overlooked as nutrient• Vital to life

– 8 cups required/day– Derives from a variety of resources.– Present in foods and produced in metabolism.

• Is a solvent, lubricant, medium for transport, chemical processes, and temperature regulator.

• Makes up majority of our body (60%).• Yields no energy.

Nutrient composition of diets and the human body

• Food you eat provides nutrients and energy for body to function.

• Quantities of nutrients we eat vary.– Pro + fat + CHO = 500g.– Minerals = 20g.– Vitamins < 300mg.

• Nutrient content of foods varies.

• Nutrient composition of body differs from that of the food we eat.

You aren’t what you eat

Energy sources

• CHO: 4 kcal/gm• Protein: 4 kcal/gm• Fat: 9 kcal/gm• (Alcohol: 7 kcal/gm)• Adjusted for

digestibility • Accounts for

substances (in food) not available for energy use

Foods generally provide more than 1 energy source

Vegetable oil is 100% fat.

Uses of energy

• To build new compounds

• For muscular movements

• For nerve transmissions

• For ion balance

Energy expressed as calories on a nutrition label

• Per serving – CHO: 15g x 4 kcal/g = 60 kcal– PRO: 3g x 4 kcal/g = 12 kcal– FAT: 1g x 9 kcal/g = 9 kcal– TOTAL: 81 kcal, rounded down to 80

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Energy on food labels expressed as calories

• A measurement of energy• “the amount of heat it takes to raise the temperature of 1

gram of water by 1 degree Celsius”• A kcal is “the amount of heat it takes to raise the

temperature of 1000 grams (1L) of water by 1 degree Celsius”

• “Calories” on nutrition label are in kcal

Calculation of contribution to total kcals

• One day’s intake (1980 kcal)• 290 gm of CHO (x 4 kcal/gm)• 60 gm of fat (x 9 kcal/gm)• 70 gm of protein (x 4 kcal/gm)• % of kcal as CHO = (290 x 4)/1980 = 0.59 or 59%• % of kcal as Fat = (60 x 9)/1980 = 0.27 or 27%• % of kcal as PRO= (70 x 4)/1980 = 0.14 or 14%

The current state of the typical American diet

• 16% of kcals as proteins– ~66% from animal

sources

• 50% of kcals as CHO– ~50% from simple

sugars

• 33% of kcals as fat– ~60 % from animal

fatsIntake of fat and cholesterol have declinedStill excess intake of sugary foods and excess intake of fried foodsFew meet the 5-A-day requirement

Ignore alcohol

Objectives for healthy people 2010

• To promote healthy lifestyle and reduce preventable death and disease – not new.

• Increase the number of healthy people

• Reduce obesity in adults and children

• Increase intake of fruits, vegetables, and whole grain products

• Lower the intake of fat, saturated fats, and sodium

• Increase the intake of calcium and iron, reduce deficiencies.

Why am I so hungry?

• What drives us to eat?– Hunger

• Physical, internal biological drive.• Interplay between organs of GIT.

– Appetite• Psychological, external drive

• Satiety stops our drive to eat – temporarily!

The hypothalamus contributes to satiety regulation

• Feeding centers in the hypothalamus stimulate eating.– Dysfunction leads to weight loss.

• Stimulation of satiety centers in the hypothalamus stop eating.– Dysfunction causes obesity

• Blood glucose is important stimulus to both.– When BSL drops we eat– When BSL raises we stop eating

• The existence of distinct centers is simplistic.

Meal size and composition affect satiety

• The desire to eat is reduced by– Gastric distention– Intestinal absorption

• Bulky meals produce more satiety than concentrated meals

• High dietary fiber and water content increases satiety.

Hormones affect satiety

• Hormones that increase hunger– Endorphins– Cortisol– Neuropeptide Y

• Hormones that promote satiety– Leptin produced by adipose tissue

• Works with insulin.• Defects in leptin pathway – Overweight.• Inhibits neuropeptide Y.

– Serotonin– CCK

Leptin/Leptin receptor research at the Rockerfeller Institute.

Appetite

• Affected by external sources.

• Environmental• Psychological• Social customs• Economics

What influences YOUR food choices

Improving our diets• Variety of food products

available –• Make the right choices – no

good or bad food

• Eat enough of the essential nutrients

• Eat enough calcium-rich foods• Adequate fluoride and

moderation in sugar• Eat enough dietary fiber• Eat enough vitamin A• Moderation in kcals• Moderation in sodium• Moderation in fat, saturated fat

and cholesterol• Adequate fluids• Use supplements wisely

Top meal choice in U.S.

Focus on variety, try to eat with others,

Improving our lifestyles

• Be aware of problems of increased affluence.• Adequate and regular physical activity• Minimize alcohol• Don’t smoke or quit• Get adequate sleep• Minimize use of medication• No illicit drug use• Reduce stress• Seek health-care professionals regularly

Using scientific research to determine nutrient needs

• Scientific methods• Step 1 – Make

observations and generate a hypothesis

• Pose questions• Test hypotheses with

controlled experiments.• Develop theories.• Reject hypotheses that

do not support critical analysis.

Fig. 1.5

Scientific Methods

• Hypothesis• Theory• Epidemiology – disease

patterns• Designed experiments

– Animal studies– Human experiments

• Case-control study• Double-blind study

• Peer Review• Follow-up study

Data from a variety of sources can come together to support a research hypothesis

Evaluation of nutritional claims

• Inconsistencies• Reliable references?• Beware use of

testimonials• Lack of evidence• List of good and bad

foods• Beware statements that

their product can cure diseases.

• Reputable journals?• Note size and duration of

studies.

Reliable nutrition information

• Take a cautious approach to nutrition-related advice.• Get advice from

– Accredited University– Hospital dietetics department– Well known health entities (e.g., American Heart

Association, American Dietetic Association, etc.)– Registered Dietitian (RD)

• The dietary supplement health and education act (DSHEA) 1994 classified vitamins, minerals, amino acids, and herbal remedies as foods.

Review major points