Principle of biochemical alterations

1. Universities Press
Rafi M D: Textbook of Biochemistry for Medical Students (2nd Edn)
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Nutrition
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2. Universities Press
Rafi M D: Textbook of Biochemistry for Medical Students (2nd Edn)
Principles of Nutrition

3. Universities Press
Rafi M D: Textbook of Biochemistry for Medical Students (2nd Edn)
Humans derive their energy from food. Foods
provide both building material and energy in
the form of nutrients to the body. Nutrients
are substances that are not synthesised in the
body in sufficient amounts and hence need be
obtained through the diet.
 Macronutrients
 Micronutrients

4. Universities Press
Rafi M D: Textbook of Biochemistry for Medical Students (2nd Edn)
CALORIFIC VALUE OF FOODS
Calorific value is the amount of heat energy
generated by burning 1 g of the food
completely in the presence of oxygen.
Calorific values of major nutrients

5. Universities Press
Rafi M D: Textbook of Biochemistry for Medical Students (2nd Edn)
Respiratory quotient is the ratio of the volume of
carbon dioxide produced to the volume of
oxygen consumed during the oxidation of food.
Carbohydrates: The volume of carbon dioxide
produced is equal to the volume of oxygen
utilised when a carbohydrate diet is consumed
(RQ is 1).
RESPIRATORY QUOTIENT (RQ)

6. Universities Press
Rafi M D: Textbook of Biochemistry for Medical Students (2nd Edn)
Lipids: The RQ of fats is relatively lower and is
about 0.7
Proteins: The RQ of proteins cannot be
measured directly. By indirect methods it is
calculated to be about 0.8.
Mixed diet: The RQ of a mixed diet is
dependent upon the relative proportions of
carbohydrates, lipids and proteins in it and in
a well balanced diet, it is approximately
around 0.8.

7. Universities Press
Rafi M D: Textbook of Biochemistry for Medical Students (2nd Edn)
For weight to remain stable, energy intake must
match energy output. Energy expenditure in
man is attributed to the following processes
that occur in the body.
1. Basal metabolic rate
2. Specific dynamic action
3. Physical activity
Apart from these three energy determinants,
certain physiological conditions like age,
pregnancy, lactation, convalescence and so on
demand extra supply of energy.
ENERGY EXPENDITURE

8. Universities Press
Rafi M D: Textbook of Biochemistry for Medical Students (2nd Edn)
BMR is defined as the minimum amount of
energy required by the body to maintain life at
complete physical and mental rest. While
determining the BMR, the person should be
awake and in a post-absorptive state.
BASAL METABOLIC RATE

9. Universities Press
Rafi M D: Textbook of Biochemistry for Medical Students (2nd Edn)
Normal values of BMR
● A healthy adult male has a BMR of about 35–
38 Cal/sq.m/h and adult female about 32–35
Cal/sq.m/h.
● More commonly, BMR is expressed as
Cal/day. For an adult male, BMR is around 24
Cal/kg body wt/day and for an adult female,
it is 22 Cal/kg body wt/day.

10. Universities Press
Rafi M D: Textbook of Biochemistry for Medical Students (2nd Edn)
FACTOR AFFECTING BMR
 Age
 Gender
 Body surface area
 Built
 Climate
 Race
 Physical activity and exercise
 Starvation
(Continued…

11. Universities Press
Rafi M D: Textbook of Biochemistry for Medical Students (2nd Edn)
 Fever
 Hormones
 Stress
Significance of BMR
…Continues)

12. Universities Press
Rafi M D: Textbook of Biochemistry for Medical Students (2nd Edn)
The fact that the consumption of food is
associated with an expenditure of energy is
well established. Utilisation of food is
associated with the expenditure of energy
resulting in increased heat production
following the ingestion of food. This is known
as specific dynamic action (SDA) or the thermic
effect of food.
Mechanism of SDA
SPECIFIC DYNAMIC ACTION
(Continued…

13. Universities Press
Rafi M D: Textbook of Biochemistry for Medical Students (2nd Edn)
SDA for different foods
The SDA for carbohydrates is 5%, for lipids
15% and for proteins, it is about 30%.
SDA for a mixed diet is taken at 10% of overall
calories.
Significance of SDA
…Continues)

14. Universities Press
Rafi M D: Textbook of Biochemistry for Medical Students (2nd Edn)
 Provided the BMR and SDA are more or less
constant, physical activity is highly variable in
different individuals.
 Energy requirements in average adults are
roughly as follows (energy required for BMR,
SDA and physical activity).
Light work 2000–2500 Cal/day
Moderate work 2500–3000 Cal/day
Heavy work 3000–4000 Cal/day
PHYSICAL ACTIVITY

15. Universities Press
Rafi M D: Textbook of Biochemistry for Medical Students (2nd Edn)
NUTRITIONAL IMPORTANCE OF
CARBOHYDRATES
 Carbohydrates
 Provide 50%–60% of the total calories.
Dietary carbohydrates are major sources of
energy.
Energy content of carbohydrates
The energy content of dietary carbohydrate is
approximately 4 Cal/g.
(Continued…

16. Universities Press
Rafi M D: Textbook of Biochemistry for Medical Students (2nd Edn)
Dietary sources of carbohydrates
1. Digestible carbohydrates
They are the chief energy sources of the
body. E.g. starch, glycogen, sucrose,
lactose, glucose, fructose.
2. Non-digestible carbohydrates
Also known as dietary fibre. Though they
are non-calorigenic they exert certain
beneficial effects in the body, e.g. cellulose,
hemicellulose, pectins, gums.
…Continues)
(Continued…

17. Universities Press
Rafi M D: Textbook of Biochemistry for Medical Students (2nd Edn)
Common sources of digestible carbohydrates
include cereals (rice, wheat) (60%–80%), pulses
(50%–60%), roots and tubers (20%–40%), bread
(50%–60%), meat (40%–50%), vegetables and
fruits (30%–50%), table sugar (100%), honey
(80%).
…Continues)
(Continued…

18. Universities Press
Rafi M D: Textbook of Biochemistry for Medical Students (2nd Edn)
Sources of carbohydrates
…Continues)

19. Universities Press
Rafi M D: Textbook of Biochemistry for Medical Students (2nd Edn)
Certain non-starch polysaccharides are
resistant to digestion by enzymes of the
human small intestine and are popularly
known as dietary fibre.
DIETARY FIBRE
Role of fibre in the body
1. Function on GIT
2. Beneficial in preventing cancers
3. In diabetes mellitus
4. Hypolipidemic effect
5. Effect on obesity (Continued…

20. Universities Press
Rafi M D: Textbook of Biochemistry for Medical Students (2nd Edn)
Sources of dietary fibre
Leafy vegetables, fruits, other vegetables,
legumes and rice bran are rich sources of fibre.
…Continues)

21. Universities Press
Rafi M D: Textbook of Biochemistry for Medical Students (2nd Edn)
Glycemic index curve
GLYCEMIC INDEX
(Continued…

22. Universities Press
Rafi M D: Textbook of Biochemistry for Medical Students (2nd Edn)
Glycemic index of some common foods
…Continues)

23. Universities Press
Rafi M D: Textbook of Biochemistry for Medical Students (2nd Edn)
NUTRITIONAL IMPORTANCE OF FATS AND LIPIDS
Sources of dietary lipids
Food items such as butter, ghee, various
vegetable oils and fish oils, milk and milk
products, egg, meat, pulses and cereals are
the dietary sources of fats and lipids.
(Continued…

24. Universities Press
Rafi M D: Textbook of Biochemistry for Medical Students (2nd Edn)
Composition of oils and fats
…Continues)

25. Universities Press
Rafi M D: Textbook of Biochemistry for Medical Students (2nd Edn)
Linoleic acid and linolenic acid are
considered to be two essential fatty acids
(EFA) because neither can be synthesised in
the human body.
ESSENTIAL FATTY ACIDS

26. Universities Press
Rafi M D: Textbook of Biochemistry for Medical Students (2nd Edn)
● Cereals, pulses and vegetables do not
contain cholesterol, which is obtained only
from foods of animal origin. It is well
known that high cholesterol levels (>240
mg/dl) are associated with increased risk
of coronary artery disease.
● In normal individuals, the cholesterol level
in the blood ranges between 150–200
mg/dl (desirable <180 mg/dl).
CHOLESTEROL AND HEART DISEASE
(Continued…

27. Universities Press
Rafi M D: Textbook of Biochemistry for Medical Students (2nd Edn)
Cholesterol content of various foods of animal
origin
…Continues)

28. Universities Press
Rafi M D: Textbook of Biochemistry for Medical Students (2nd Edn)
NUTRITIONAL IMPORTANCE OF PROTEINS
Essential amino aicds
Amino acids and their nutritional requirements

29. Universities Press
Rafi M D: Textbook of Biochemistry for Medical Students (2nd Edn)
NITROGEN BALANCE
 Negatie nitrogen balance
 Positive nitrogen balance
Nitrogen balance in the body.

30. Universities Press
Rafi M D: Textbook of Biochemistry for Medical Students (2nd Edn)
NUTRITIONAL VALUE OF PROTEINS
Dietary sources of proteins
Meat, eggs, fish, milk are good sources of
protein. Legumes, beans, peanuts, peas,
soyabean are the best plant sources.
How much protein do we need?
The recommended dietary allowance (RDA) is
0.75 g/kg body weight/day is sufficient for a
normal adult.

31. Universities Press
Rafi M D: Textbook of Biochemistry for Medical Students (2nd Edn)
Common dietary sources and their protein
content

32. Universities Press
Rafi M D: Textbook of Biochemistry for Medical Students (2nd Edn)
Biological value is the ratio of the amount of
nitrogen retained in the body and nitrogen
absorbed.
Nitrogen retained
BV = × 100
Nitrogen absorbed
Though BV is a widely used index to express the
nutritional value of proteins, it has certain
inherent defects. It does not take into account
the nitrogen which is lost during digestion and
hence it may not provide an accurate nutritional
assessment of proteins.
BIOLOGICAL VALUE (BV)

33. Universities Press
Rafi M D: Textbook of Biochemistry for Medical Students (2nd Edn)
This is a better nutritional index compared to
BV as it takes into account the factor of
digestion. It is the ratio between the nitrogen
retained in the body to total nitrogen ingested.
Nitrogen retained
NPU = × 100
Nitrogen ingested
NET PROTEIN UTILISATION (NPU)

34. Universities Press
Rafi M D: Textbook of Biochemistry for Medical Students (2nd Edn)
The quality of a protein can be determined by
its ability to produce growth. It is the
assessment of weight gain per gram of protein
taken. PER is the measurement of the ability of
a protein to promote growth in an animal.
Gain in body weight (g)
PER =
Protein ingested (g)
PROTEIN EFFICIENCY RATIO (PER)

35. Universities Press
Rafi M D: Textbook of Biochemistry for Medical Students (2nd Edn)
A balanced diet is composed of a variety of
foods which contain all the essential nutrients
such as carbohydrates, fats, proteins and
micronutrients in the right proportions
BALANCED DIET
(Continued…

36. Universities Press
Rafi M D: Textbook of Biochemistry for Medical Students (2nd Edn)
A mixed diet for an average adult; (weighing 60 kg)
…Continues)

37. Universities Press
Rafi M D: Textbook of Biochemistry for Medical Students (2nd Edn)
 Calorie requirement has to be assessed
based on age, gender, build, health status
and physical activity.
 Protein requirement has to be assessed
based on age, gender, build, health status
and physical activity.
PRINCIPLES OF PRESCRIBING A DIET
(Continued…

38. Universities Press
Rafi M D: Textbook of Biochemistry for Medical Students (2nd Edn)
 Protein requirement can be calculated as
0.8 g/kg body weight/day. During growing
age, pregnancy and lactation it can be more
than 2 g/kg body wt. Protein can be obtained
as animal protein or mixed vegetable
protein. The calorie yield from a protein diet
should be 10%–15% of total calorie
requirements.
…Continues)
(Continued…

39. Universities Press
Rafi M D: Textbook of Biochemistry for Medical Students (2nd Edn)
● Fats can provide 20%–25% of total calorie
requirements of the individual. Visible (fats and
oils) should be restricted to not more than
20 g/day for a healthy adult.
However, in various physiological states it can be
enhanced, such as growing children (25 g),
pregnant women (30 g) lactating mothers (45 g).
It is advisable that obese individuals, old people
and persons at risk of cardiovascular disease
restrict fat content to less than 20 g a day.
Different vegetable oils can be used to balance
the composition of SFA, MUFA and PUFA to 1:1:1.
…Continues)
(Continued…

40. Universities Press
Rafi M D: Textbook of Biochemistry for Medical Students (2nd Edn)
● Choose a diet with plenty of whole grains,
vegetables and fruits and green leafy foods
which contain both digestible carbohydrates
and dietary fibre. Ideally 55%–65% of calories
can be obtained from carbohydrate diet.

41. Universities Press
Rafi M D: Textbook of Biochemistry for Medical Students (2nd Edn)
Food pyramid (a guide to balanced diet).
FOOD GUIDE PYRAMID

42. Universities Press
Rafi M D: Textbook of Biochemistry for Medical Students (2nd Edn)
PEM is mostly seen in young children due to
malnutrition. The clinical picture of PEM is
manifested in two forms.
1. Kwashiorkor; 2. Marasmus
Kwashiorkor
Kwashiorkor represents protein malnutrition in
children characterised by edema.
Marasmus
Marasmus is the result of severe malnutrition in
infants characterised by severe muscle wasting.
PROTEIN - ENERGY MALNUTRITION (PEM)
(Continued…

43. Universities Press
Rafi M D: Textbook of Biochemistry for Medical Students (2nd Edn)
Comparison between kwashiorkor and marasmus
…Continues)