2. Anabolism
It is the conversion of small molecules with energy
consumption to large molecules.
e.g. Amino acids → Proteins.
Glucose → Carbohydrates.
Fatty acids → Fats
3. Catabolism
It is the conversion of large
molecules with energy production
into small molecules.
Glucose (C6H12O6) +6O2 =
6CO2 + 6H2O + Energy
These chemical reactions lead to
release of large amount of energy.
4. Metabolism
All chemical reactions occurring in living cells
that make it possible to continue living.
There is a balance between Anabolism and
Catabolism. This results in constant body weight.
More anabolism → ↑ body weight e.g. in
children.
More catabolism →↓ body weight e.g in
hyperthyroidism
5. Kilo Calorie (Kcal or C):
It is the Amount of heat necessary to raise the
temperature of 1Kg of water one °C from 15°C to 16°C.
Kilocalorie (Kcal or C) = 1000 calorie (c).
In nutrition C capitalized or not, Kcal or Kc refers to the
same amount of energy ,no need to convert
1 kilojoule = 0.24 Calories.
6. Physical and physiological heat value
Any substance (carbohydrate, fat or protein) can be oxidized inside
the body or outside the body with liberation of heat.
Physical heat: is the amount of heat in calories which are produced
by complete oxidation of food outside the body (by burning with
pure O2).
This can be measured using Bomb calorimeter in which the food is
ignited by an electric spark.
Physiological heat: is the amount of energy in calories which are
produced by complete oxidation of food inside the body.
7. We notice that:
In the body, calorie values obtained for carbohydrate & fat are similar to that
outside the body.
The Physiological heat value of proteins is less than their Physical heat value
why?
Because the nitrogen of protein (which represents 16% of the protein molecule)
are not oxidized because its oxidation would produce large amounts of nitric acid
→ ↓ Blood pH to fatal levels. So it is converted into Nitrogenous substances
mainly urea which is excreted in urine.
8. Respiratory quotient (RQ)
It is the ratio between the volume of CO2 produced to
the volume of O2 consumed in the same time of
metabolism.
9. Significance of RQ determination:
1.Determination of the nature of substance
oxidized in different times and conditions.
2.For calculation of the metabolic rate.
3.Evidence for transformation of food
substance into another
10. The RQ is an index of the nature of the
substances oxidized in different tissues and
conditions:
Substance oxidized RQ
carbohydrates 1.0
protein 0.8
fat 0.7
11. For carbohydrates
C6H12O6 + 6O2 → 6CO2 + 6H2O + Energy
RQ = 6Co2/6 O2 = 1
So, for each molecule of O2 consumed, there is a molecule of
CO2 is produced.
This is because carbohydrates contain enough O2 in their
molecules to oxidize all the H+ atoms present & form H2O.
Extra O2 is needed from the atmosphere, is used to oxidize
carbon atom and appears as CO2.
12. For fats :
C18H36O2 + 26 O2 →18 CO2 + 18 H2O + energy
RQ = 18 Co2/ 24 O2 = 0.7
This is because oxygen atoms present in fat & protein
molecules are less than that for carbohydrates. So,
excess O2 is needed from atmosphere to oxidize the
hydrogen and carbon atoms.
For proteins RQ was found to be 0.8.
Mixed food RQ = 0.85.
13. Different tissues and conditions:
RQ of the brain is 1.0 (0.97- 0.99) indicating that
glucose is its principal fuel.
RQ in diabetes mellitus is 0.7 indicating that fat is
the chief source of energy.
14. Calculation of metabolic rate:
By determination of the O2 Heat value from RQ
(by metabolic tables).
Metabolic rate = O2 Heat value X O2 consumed.
O2 Heat value: is the amount of heat in calories
resulting from oxidation of a food substance
using one liter of O2.
16. Evidence for the transformation of one
food substance into another:
Transformation of carbohydrates into fats (lipogenesis)
RQ above unity. (A substance rich in O2 is converted
into a substance poor in O2 so, O2 consumption is ↓ and
CO2 is produced without atmospheric O2 consumption).
Transformation of fats or proteins into carbohydrates
(gluconeogenesis)→ RQ below unity. (due to ↑ O2
consumption & ↓ and CO2 production)
17. Basal metabolic rate (BMR)
It is the amount of energy production in unit time (one hour)
under basal conditions
1- comfortable temperature (20 -25c dressed)
2- last meal 12-14 hrs.
3- complete physical and mental rest (awake)
It represents the amount of energy required to perform all the
essential activities of the body systems as CNS, heart,
respiration, kidneys & skeletal muscle tone i.e. it represents the
unavoidable cost of life.
It isn’t the minimal energy expenditure because it can be
reduced by many factors as sleep.
18. Measurement:
Measured by direct or indirect calorimeter and divide on
body surface area.
BMR is expressed in ……… Calories / m2 / hr.
Normally in adults = 40 Calories / m2 / hr ± 15 %.
BMR is expressed as a % deviation from the normal
standard thus, BMR of 60 Calories / m2 / hr is expressed
as + 50% above the normal standard.
19. Clinically, BMR
In-body devices used to calculate the BMR.
Simple equation for rough estimation of BMR;
for males= BW in Kg * 24.2
For females =BW in Kg * 22
Average adult must take about 2000 C/day to meet his
basal needs which represents about 60% of energy
requirements all over the day. Extra energy is required
to perform the daily activities.
daily caloric requirement = BMR * activity factor (1.2-
1.8 according to individual level of activity)
20. Factors affecting BMR:
1- Age:
In A newly born infant →25 Calories / m2 / hr (so infants are greatly
susceptible to cold).
21. 2- Sex
BMR in females is lower than in males by 7 %.
It may be due to greater stores of fat in females
(estrogen) and greater muscle mass in male
(testosterone)
Testosterone has greater thermogenic effects than
progesterone.
Males usually has greater surface area and height than
females
22. 3- Physical habits: Athletics have higher BMR (by
10 %) than ordinary persons due to ↑in muscle
mass.
4- Dietetic habits: The habit of eating protein rich
diet for long period ↑ BMR by 10% than eating
carbohydrates.
5- Climate: BMR is higher in cold and temperate
zones (e.g. Eskimo) than in hot zones by 10%.
23. 6) Race:
Pure races e.g. Chinese & Indians have lower BMR than mixed races as
Americans & Egyptians.
Dark races have lower BMR than white races.
7) Pregnancy:
BMR ↑ gradually during pregnancy until it is doubled at the end of
pregnancy due to:
Increased thyroxine, cortisol & sex hormones.
Added metabolism of fetus.
8) Sleep: ↓ BMR by about 10%.
26. Specific dynamic action (SDA)
It is the power of the food to stimulate the metabolic
rate (thermic effect of food).
The metabolic rate starts to ↑ 1 hour after taking food.
Reaches the maximum after 3:4 hours.
↓ to basal levels 12:18 hours after food intake.
It results from the different chemical reactions
associated with food metabolism in the body.
27. SDA depends on:
1. Type of food ingested: It is 30% for protein,6% for carbohydrates, 4% for fat.
2. Quantity of food: SDA is proportional to the quantity.
3. External temperature:
- If external temperature is 33ᵒ C → SDA is maximal.
- If external temperature is 5ᵒ C→ SDA disappears because it is retained in the
body to maintain body temperature.
28. N.B:
Energy released due to SDA is a waste heat but it is
useful on exposure to cold. It helps in maintaining body
temperature constant so; high protein diet results in
discomfort in hot weather but not in cold one.
Notes:
1. Liver is essential for SDA.
2. GIT glands or endocrine glands aren‟t a cause of SDA.
3. SDA isn’t related to the biological value of proteins i.e.
A low biological value protein produces the same SDA
as a high biological value protein.
