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Chemical changes occur in the body.
1) Catabolic reactions:
* Definition: breakdown of large organic molecule with release of energy:
Protein (CHO or fat) CO2 + H2O + Energy. [ATP] used as:
a) Work energy. 25% used for essential functions.
b) Heat energy. 75%
2) Anabolic reactions:
Synthesis of organic large molecules with uptake of energy.
The rate of heat production from the body per
The rate of energy production [kcal] / unit time (on hour) /m2
*Measured under 3 basal conditions:
1- Complete physical & mental rest:
for at least 1/2 an hour but without sleep as
decreases the BMR by 10%.
2- Post - absorptive state:
12-14 hours after the last meal to avoid specific
dynamic action (SDA).
3- In a comfortable external temperature:
Neither shivering nor sweating
also known as thermic effect of food (TEF)
or dietary induced thermogenesis (DIT), is the
amount of energy expenditure above
the basal metabolic rate due to the cost of
processing food for use and storage
The thermic effect of food is one of the
components of metabolism . A commonly
used estimate of the thermic effect of food is
about 10% of one's caloric intake, though the
effect varies substantially for different food
components. For example, dietary fat is very
easy to process and has very little thermic
effect, while protein is hard to process and
has a much larger thermic effect.
The thermic effect of food is the energy
required for digestion, absorption, and
disposal of ingested nutrients. Its magnitude
depends on the composition of the food
Carbohydrates: 5 to 15% of the energy
Protein: 20 to 35%
Fats: at most 5 to 15%
Rate of energy input [food] = Rate of energy
1] If energy input > energy output :
+ve energy balance.
Increase the body weight.
2] If energy input < energy output :
-ve energy balance.
Decrease the body weight.
The adult basal level of caloric intake = 2000
* Normal standard:
For adult man = 40 Kcal / hour / m2 ± 15%.
* Clinically: it is expressed as % deviation from normal standard:
E.g. if BMR = 60 Kcal /Hr/ m2. ……….Thus, it is + 50%.
* BMR is expressed per unit surface area and not per unit body
It is through the skin that most heat is lost to the atmosphere.
* It is the unavoidable cost of life:
I.e. metabolic activities of heart, respiratory muscles, liver,
I] Physiological factors.
II] Pathological factors.
Newly born infants = 25 KCal/h/m2
2- 5 years = 60 KCal/h/m2
Puberty = 55 KCal/h/m2
Adult = 40 KCal/h/m2 ±15%
Old age:1 Kcal decrease /10 years
2] Sex: BMR is decreased in female than male by 7% due to:
Greater fat stores [Fat has little metabolic activity].
3] Pregnancy and lactation: increase BMR due to:
++ Thyroid activity, & the added metabolism of the fetus.
4] Sleep: decrease BMR by 10% due to:
-- Muscle tone & --sympathetic activity.
5] Environmental temperature:
Cold shivering increase the MR maintains normal body temperature.
Hot increase the body temperature increase the MR.
6] Food: Increase the MR by the specific dynamic action.
7] Muscular exercise: Increase the MR.
Factors that increase MR:
1) Hyperthyroidism ++MR up to + 100% [except brain].
a) ++ GH ++ MR.
b) ++ TSH ++ T4 ++ MR.
3) Hyperadrenalism: ++ catecholamines ++ MR.
4) Fevers: increase the body temperature ++ MR.
5) Heart failure due to ++ activity of respiratory muscles to
6) Blood diseases: as polycythemia - the hematocrit (the volume
percentage of red blood cells in the blood) is elevated- due to
over activity of bone marrow.
increase in the number of red blood
cells ("absolute polycythemia") or
decrease in the volume of plasma ("relative
1) Hypothyroidism: --MR by 40% of the normal.
2) Hypopituitarism: due to atrophy of endocrine
-- body temperature by 1oC--MR by 13%.
4) Under-nutrition: due to -- energy producing cell
5) Hypo-function of adrenal cortex: due to --
Factors regulating the activity of appestate center:
1) Psychological conditions:
Vision, smell of food affect centers in limbic lobe.
2) Receptors in the mouth & esophagus:
Monitoring food intake.
3) Stomach distension: stop of feeding.
4) GIT hormones and insulin: stimulate satiety center.
5) The blood levels of glucose, amino acids, fatty acids &
glycerol affect hypothalamus.
6) SDA of food ++body temperature inhibition of food
7) Cold environment ++ food intake.
N.B Satiety center and appetite center are located in the
a) The lipostatic hypothesis:
* Adipose tissue:
Humoral signal [proportionate to the amount of fat].
Acts on the hypothalamus --food intake &++energy
b) The gut peptide hypothesis:
* Food in the GIT secrete GIT polypeptides.
Acts on the hypothalamus --food
c) The glucostatic hypothesis:
* Glucose utilization in the hypothalamus sensation of
d) The thermostatic hypothesis:
* --Body temperature ++ appetite.
* ++Body temperature -- appetite.
1 – burn cho
2- burn stored glycogen
3- burn fat
4- burn proteins of muscles
5- burn proteins of blood plasma proteins