In this article we will discuss about the Basal Metabolism:- 1. Definition of Basal Metabolism 2. Conditions for Measurement of Basal Metabolism 3. Factors Influencing 4. Measurement 5. Significance.

Contents:

  1. Definition of Basal Metabolism
  2. Conditions for Measurement of Basal Metabolism
  3. Factors Influencing Basal Metabolic Rate
  4. Measurement of Basal Metabolic Rate
  5. Significance of Basal Metabolic Rate

1. Definition of Basal Metabolism:

The total heat produced or the energy spent by the body under conditions to perform minimum possi­ble work is known as basal metabolism. The lowest level of energy production consonant with life is the basal metabolic rate (BMR).

2. Conditions for Measurement of Basal Metabolism:

a. Post-absorptive State:

The patient should not take anything by mouth for the past 12 hours.

b. Complete mental and physical relaxation.

c. Patient should be awake.

d. Recumbent position during the test.

e. Environmental temperature should be be­tween 20°C-25°C.

3. Factors Influencing Basal Metabolic Rate:

a. Surface Area:

The BMR is directly re­lated to the surface area of the subject. Larger the surface area greater would be the BMR.

b. Age:

The BMR is inversely proportional to age. Children have larger BMR than adults.

c. Sex:

Males have higher BMR than fe­males. The BMR of females declines more rapidly between the ages of 5 and 17 than that of males.

d. Climate:

The BMR is lower in warm cli­mates.

e. Racial Variations:

The BMR of oriental women living in the USA is 10 per cent below the standard BMR of American women of the same age.

f. Habit:

Persons accustomed to heavy ex­ercise or hard physical work have a higher BMR than those involved in sedentary work.

g. State of Nutrition:

The BMR is decreased in starvation and undernourishment.

h. Pregnancy:

The BMR is not changed dur­ing pregnancy. The higher values of BMR in late pregnancy is due to the BMR of the foetus.

i. Disease:

The BMR is increased in infec­tious and febrile diseases. The increase is usually proportional to the rise of the tem­perature. The BMR is also increased in increased activity of cells and, therefore, it increases in leukemia, cardiac failure, hypertension, polycythemia, dyspnea, and some types of anemia.

j. Effects of Hormones:

The BMR is in­creased in hyperthyroidism and decreased in hypothyroidism. In adrenal insuffi­ciency (Addison’s disease), the BMR is subnormal.

k. Drugs:

Caffeine and benzidine increase the BMR.

l. Emotion:

The BMR is increased in emo­tional stress.

m. Diet:

The BMR of strict vegetarians is 11% lower than that of meat eaters.

4. Measurement of Basal Metabolic Rate:

a. The BMR can easily be measured either by the apparatus of Benedict and Roth (closed circuit device) or by Douglas bag method (open circuit device). Benedict-Roth’s apparatus is abundantly used in hospitals and laboratories.

b. This method provides sufficient accuracy only by measuring the oxygen consump­tion of the patient for two 6-minute peri­ods under basal conditions. The average of two such readings is multiplied by 10 to obtain the hourly consumption of oxy­gen and then multiplied by 4.825 kcal, the heat produced by one litre of oxygen. This gives the total heat produced in kcal/ hour.

c. This above value is divided by the sur­face area of the subject to get the BMR in C/hr/sq.m.

The simple classical formula of Du Bois is ap­plied which is as follows:

A = H0.725 x W0.425 x 71.84,

where A = surface area in cm2.

H = height in cm.

W = weight in kg.

The above value obtained is in sq. cm. This should be divided by 10,000 to get the surface area in sq. metre.

A BMR between – 15% and + 20% is consi­dered normal. The BMR may exceed + 50% to + 75% in hyperthyroidism. In hypothyroidism, the BMR may be – 30% to – 60%. The normal BMR is 39.5 C/m2/hr. The BMR increases as much as 600%- 800% over basal during exercise.

5. Significance of Basal Metabolic Rate:

a. The determination of BMR is the princi­pal guide for diagnosis and treatment of thyroid disorders.

b. The BMR – 10% of the normal develops moderate hyperthyroidism. In severe hypothyroidism, the BMR may be decreased to 40 to 50 per cent below normal.

c. It aids to know the BMR to have an idea of the total amount of food or calorie re­quired to maintain body weight or calo­rie.

d. The BMR is below normal in starvation, under nutrition, hypothalamic disorders, Addison’s disease, and lipoid nephro­sis.

e. The BMR is above normal in fever, diabe­tes insipidus, leukemia and polycythe­mia.

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