Human Nutrition 3(3+0)

Lesson 9 : BMR-Methods of Measurements and Factors Affecting BMR

Factors Affecting the Basal Metabolic Rate

1. Body size
   The B.M.R. is closely related to the body surface area. Basal metabolism is less directly related either to the height or weight of the individual.
2. Age
   the B.M.R. is higher in infants and young children than in adults.
3. Females have slightly lower B.M.R. than males.
4. Body composition
   The B.M.R. is directly related to the lean body mass. Persons with well developed muscles will have a higher B.M.R.than obese person whose higher body weight is due to adipose tissue.
5. Climate
   In persons living in tropical climates, the B.M.R.is about 10 percent less than those living in temperate zones.
6. S.D.A. of Food
   Food has a stimulating effect on B.M.R. If a person in post-absorptive state is given food, the B.M.R. has been found to increase by about 8 per cent. This is known as the Specific Dynamic Action of food.
7. Undernutrition and Starvation
   prolonged undernutrition or starvation causes a reduction of about 10-20 per cent less than in B.M.R.
8. Sleep
   The B.M.R. in sleep is about 5 percent less than in the basal metabolic state.
9. Fever
   Fever increases the B.M.R. For every 10F rise in body temperature B.M.R. increases by about 7 percent. A person with high fever (105 0 F) would have an increase of 50 per cent in the B.M.R.
10. Physical Activity
    If an individual takes physical exercise about half-an –hour before the determination of B.M.R., appreciable increase in the B.M.R. is observed.
11. Fear and Nervous tension
    Fear and nervous tension during the test increase the B.M.R.
12. Thyroid
    Hypothyroidism decreases B.M.R. up to 30 per cent and hyperthyroidism may cause an increase in B.M.R. up to 100 percent depending on the severity of the condition.
13. Adrenaline
    Injection of 1mg of adrenaline increases the B.M.R. by about 20 per cent for a few hours.
14. Anterior Pituitary
    The anterior pituitary influences B.M.R. through its thyrotropic hormone, the B.M.R. being low in hypoactivity and high in hyper-activity of the glands.
15. Other Diseased Conditions
    An increase in B.M.R. has been observed in splenomegly and lymphatic leukemia.