Food & Nutrition for undergraduate medical biochemistry course

1. FOOD & NUTRITION
DR. FARHANA ATIA
Assistant Professor
Department of Biochemistry
Nilphamari Medical College, Bangladesh

2. NUTRIENTS
• Nutrients are constituents of food necessary to
sustain normal functions of the body.
• Essential nutrients obtained from diet-
 Energy sources
- Carbohydrate
- Protein
- Fat
 Essential amino acids
 Essential fatty acids
 Vitamins
 Minerals

3. Nutrients may be-
1. Macronutrients
– Needed in large amount [gm/d]
– Provide all energy
– Maintain optimal health &
– Prevent chronic disease
– Carbohydrate, protein, fat
2. Micronutrients
– Needed in laser amount [mg/d]
– Vitamins, minerals

4. • Diet: Kind of food on which a person or
group lives.
• Balanced diet: Balanced diet is one which
contains a variety of foods in such
quantities & proportions that the need for
energy & all nutrients is adequately met for
maintaining health, vitality & general well
being.

5. Balanced diet
• Accepted means to safeguard
a population from nutritional
deficiencies
• Principles: for adult percent
of total calorie intake
– Protein: 10-35%
– Fat: 20-35%
– Carbohydrate: 45-65%. Rich
in natural fiber

6. Dietary reference intake (DRI)
• Estimates of the amount of nutrients required to
prevent deficiencies and maintain optimal health
& growth. Components are-
Estimated average requirement (EAR)
Recommended Dietary Allowance (RDA)
Adequate Intake (AI)
Tolerable Upper Intake Level (UL)

7. Dietary reference intake (DRI)
• EAR: The average daily nutrient intake level
estimated to meet the requirement of one half
of healthy individuals in a particular life stage
(age) and gender group.
• RDA: The average daily dietary intake level that
is sufficient to meet the nutrient requirement of
nearly all (97-98%) individual in a life stage &
gender group.
– Not the minimal requirement
– Intentionally set to provide a margin of safety

8. • AI: It is based on nutrient intake by a group of
apparently healthy people.
– Used instead of RDA if sufficient scientific
evidence is not available to calculate
• UL: Highest average daily nutrient intake level
that is likely to pose no risk of adverse health
effect to almost all individuals in the general
population.
– Useful in taking fortified food & dietary
supplements.
Dietary reference intake (DRI)

9. Estimated Energy Requirement (EER)
Average dietary energy intake predicted to
maintain an energy balance (consumption=
expenditure). Depends on-
– Age
– Gender
– Height (& weight)
– Level of physical activity
– Also genetic difference, body composition,
metabolism, behavior

10. Energy Requirement
Average requirement
• Sedentary adult : 30 kcal/kg/day
• Moderately active : 35 kcal/kg/day
• Very active : 40 kcal/kg/day
Energy content of food
– Calculated by heat released by total combustion
of food in a calorimeter
– Expressed in kcal or Cal

11. Energy Requiring Process
• Energy requirements are estimated by
measurement of energy expenditure.
• Total energy expenditure (TEE) depends on three
energy requiring processes in body-
1. Basal metabolic rate (BMR/RMR)
2. Thermic effect of food (SDA)
3. Physical activity
BMR
Physical
activity
SDA

12. BMR
• The energy expended by an individual when
– At rest, but not asleep
– Under controlled condition of thermal neutrality
– After 12 hours of last meal
• Reflects lean muscle mass (highest in men & young)
• Represents the energy required to carry out
– Respiration
– Blood flow
– Ion transport/ exchange

13. BMR
 50-70% of TEE
70 kg adult male: 1800 kcal/ day
50 kg adult female: 1300 kcal/day
• Can be determined
Directly by measuring heat output from body
Normally estimated indirectly from O₂
consumption (or CO₂ production)
• Respiratory quotient (RQ) = CO₂ produced/O₂
consumed
• RQ reflects the metabolic fuel being oxidized

14. Factors affecting BMR
• Gender
• Age
• Height & weight
• Physical activity
• Hormones
• Environmental
• Starvation
• Fever
• Disease
• Race

15. SDA (Specific Dynamic Action)
• There is a considerable increase (up to 30%) in
metabolic rate after meal during
–Secretion of digestive enzyme,
–Absorption of food
–Metabolism of food (synthesizing reserves
of glycogen, triacylglycerol, & protein)
This is called SDA of food/ Thermic effect of
food/ diet-induced thermogenesis.
• 5-10% of TEE

16. Physical Activity
• Muscular activity provides greatest variation
in TEE.
• Energy cost of physical activity is expressed
as multiple of BMR
• For sedentary worker : 1.1-1.2 x BMR
≈30-50% more calories than BMR
• For vigorous exertion : 6-8 x BMR
≥100% calories above BMR

17. Physical Activity
BMR 60% 1300 kcal
SDA 10% 210 kcal
PA 30% 630 kcal
• Estimated TEE in a healthy 20 year old 165
cm tall, weighing 50 kg, engaged in light
activity

18. Macronutrients
• Provide energy
• Deficiency leads to marasmus
Composed of Acceptable range (For adult)
Carbohydrate 45-65%
RDA (men & women): 130 g/day
Protein 10-35%
RDA: men-56 g/d; women- 46 g/day
Fat 20-35%
ω-6 PUFA: 5-10%; ω-6 PUFA: 0.6-1.2%
Fiber Men- 38gm; Women- 25gm

19. Dietary Fats
• Strongly influence coronary heart disease (CHD)
• Type of fat is more important risk factor than total
amount of fat
• Most important & abundant fat in diet : TAG
– Saturated fat
– Monounsaturated fat
– Polyunsaturated fat
– Trans fat
– Dietary Cholesterol

20. Saturated fat
• Associated with ↑ total plasma cholesterol, LDL-C
• ↑ risk of CHD, Colon cancer
• Recommended intake : <10% of total calorie
• Food source
– White, visible fat found in meats
– Dairy products
• Whole milk
• Butter, Cream
• Hard cheeses
– Coconut and palm oils

21. Monounsaturated fat
• TAG containing fatty acid with one double
bond
• Lower total plasma cholesterol & LDL-C
• Maintain/ increase HDL-C
• Recommendation : 10-20% of calorie intake
• Source- Plant based oil (olive oil)

22. Polyunsaturated Fat
• ↓ Incidence of CHD (influenced by the location of
double bonds in PUFA)
• ω-6 Fatty acid : linoleic acid
– Long chain FA (18:2 [9,12])
– ↓ plasma cholesterol, LDL-C & also HDL-C
– Source: Nuts, avocados, olive, soybeans,
sunflower & corn oil
– Acceptable range 5-10%

23. Polyunsaturated Fat
ω-3 Fatty acid
• Long chain FA eg. α-Linolenic acid (18:3 [9,12,15])
• ↓Serum TAG
• ↓ Thrombosis, suppress cardiac arrhythmias
• ↓ BP, thus reduce cardiovascular mortality
• Little effect on LDL-C, HDL-C
• Source: flaxseed & canola oil, walnuts
• Found in fish oil (2 fatty fish meal/week)
• Acceptable range: 0.6- 1.2% of total calories

24. Trans fatty acids
• Chemically unsaturated but behave like saturated FA
• Elevate LDL-C, lower HDL-C; so ↑ risk of CHD
• Formed during hydrogenation of vegetable oil (in
manufacture of margarine)
• Found in commercial baked goods (cookies), deep
fried foods
• Virtually no trans fat is permitted in food

25. Cholesterol
• Found only in animal product
• Plasma cholesterol arise from diet or endogenous
biosynthesis
• Increased risk of CHD correlates with
– Elevated total cholesterol
– ↑ LDL-C
• ↑ HDL-C associated with ↓ risk of heart disease
• ≤ 300 mg/day in diet is recommended

26. Dietary Protein
Provide Essential Amino Acids
Quality of protein: Ability to provide EAA
Daily requirement (10-35% of total calorie)
• Adult: 0.8 gm/kg (56 gm for 70 kg person)
• Athletes: 1gm/kg
• Infant: 2gm/kg
• Pregnant & lactating women, burn patient need excess
• Protein restriction is needed in kidney disease

27. • Animal proteins-
• Meat
• Poultry
• Milk
• Egg
• Fish
• Contain all EAA in proportions required
for synthesis of human tissue protein
• Rapidly digested
High
quality
protein

28. • Proteins from plant sources
• Soybean protein
• Wheat
• Corn
• Rice
• Bean
• To increase nutritional value - combine
proteins from different plant sources
(wheat+ beans)
Lower
quality
protein

29. Dietary Carbohydrates
• Primary role- to provide energy
• Not essential nutrients because amino acids can
be converted into glucose
• Absence leads to ketogenesis & degradation of
body protein
• RDA: 130 g/day for adult & children
• Types
1. Simple sugars
2. Complex sugar
3. Fiber

30. Simple carbohydrates
• Food source
– Glucose: Fruits, syrup, honey, sweet corn
– Fructose: Honey, fruits (apple)
– Sucrose: Table sugar, molasses, maple syrup
– Lactose: Milk
– Maltose: product of digestion of polysaccharide
• Added sugar: Sugar or syrup added to foods
during processing or preparation
– Associated with obesity & type 2 diabetes
– Should not be >10% of total energy intake

31. Complex carbohydrate
• Polysaccharides, most often polymers of
glucose
• Do not have sweet taste
• Starch is abundant in plant
• Source:
– Wheat & other grains
– Potatoes, dried peas, beans
– Vegetables

32. Dietary fiber
• Non digestible, nonstarch carbohydrates & lignin
present in plants
• Provide little energy but has beneficial effects
• Soluble fiber
– Edible part but resistant to digestion & absorption
– Completely/ partially fermented by bacteria
• Insoluble fiber
– Remain intact in digestive tract
• Functional fiber
– Extracted/ synthetic fiber, commercially
– Has proven health benefit

33. Health effects of dietary fiber
• Add bulk to the diet (can absorb 10-15 times
its own weight in water)
–Softening of stool
–Reduce constipation, hemorrhoids &
diverticulosis
• ↑ bowel motility & promote bowel
movement (laxation). Thus reduce exposure
of gut to carcinogen.

34. Health effects of dietary fiber
• Soluble fiber delays gastric emptying
– Generate sensation of fullness (satiety)
–Reduce spike in blood glucose following a
meal
–Food rich in fiber show low glycemic index
• Lower LDL-C level by increasing fecal bile acid
excretion & interfering with bile acid
absorption

35. Glycemic Index
• The increase in blood glucose after a test dose
of carbohydrate compared with that after an
equivalent amount of glucose is known as the
GI.
• GI ranks carbohydrate-rich foods on a scale of
1-100
• Low GI is <55; High GI is ≥70
• Glycemic load (GL): How much a typical serving
size of a food raises blood glucose.
• A food can have a high GI & a low GL (carrots)

36. Clinical importance of low-GI diet
– Beneficial for health
– Create a sense of satiety
for longer period, so
reduce calorie intake.
– Causes less fluctuation in
insulin secretion, so
improves glycemic
control in diabetic
individual
Some food produce a rapid rise
followed by a steep fall of blood
glucose level, whereas others result
in a gradual rise followed by a slow
decline