Basal Metabolic Rate (BMR)

Definition of BMR

• Is the rate of basal metabolism in a given person at a given time and situation.
• It constitutes one half of the calorie requirements of an individual.

Conditions Necessary For BMR Test

To ensure accuracy:

1. The subject must be in fasting or post-absorptive state, at least 12 hours after meals and it is usually taken in the morning.
2. The subject must be awake, lying quietly, free form physical fatigue, nervousness or tension as this causes an increase in heat production.
3. The environmental temperature should be between 20-25?C so that the subject can maintain his body temperature.

Calculation of BMR

1. A simple method for the calculation of the BMR is to use the rule of thumb 1 kcal per kg hour per adult male and 0.9 kcal per kg per hour for adult female. An individual whose IBW is 50 kg has a basal metabolic energy need of 1200 kcal per day (50 x 1 kcal x 24 hrs). This value however may not be applicable for obese or lean individuals.

Example: Male 75 kg

= 1 kcal x 75 x 24

= 1800 kcal

Female 65 kg

= .9 kcal x 65 x 24

= 1404 kcal

2. Harris-Benedict formula, developed in 1909, using information on weight, height, age and sex.

Example: Males

REE = 66 + [13.7 x wt(kg)] + [5 x ht(cm)] – [6.8 x age(yr)]

Female

REE = 655 + [9.6 x wt(kg)] + [1.8 x ht(cm)] – [4.7 x age (yr)]

3. Another method used in obtaining the metabolic or fat free body size is called the Biologic Body Weight raised to the ¾ power.

Once the metabolic body size is known based on weight in kilograms, this figure is multiplied by 70.

A 50 kg man’s REE = 18.8 x 70 = 1,326 kcal

4. The fourth method is that developed by WHO/FAO/UNU in 1984. It uses the following equation:

1.6 x wt(kg + 879) = REE

A 50 kg man will have a REE of 1,459 kcal.

Body Weights In Kg And Metabolic Body Size (kg) ¾

Factors that Affect the Basal Metabolic Rate (BMR)

1. Surface area – the greater the body surface area or skin area, the greater the amount of heat loss will be, and in turn, the greater the necessary heat produced by the body. Muscle tissue requires more O2 than does adipose tissue.
2. Sex – women, in general, have a metabolism of about 5 to 10% lower than men even when they are of the same weight and height. Women have a little more fat and less muscular development than men.
3. Age- the metabolic rate is highest during the periods of rapid growth, chiefly during the first and second years and reaches a lesser peak through the ages of puberty and adolescence in both sexes. The BMR declines slowly with increasing age to lower muscle tone from lessened activity.
4. Body composition – a large proportion of inactive adipse tissue lowers the BMR. Athletes with great muscular development show about 5% increase in basal metabolism over non-athletic individuals.
5. State of nutrition – a decrease in mass of active tissue like in undernourishment or starvation causes a lowered metabolism often as much as 50% below normal.
6. Sleep – the metabolic rate falls approximately 10 to 15% below that of waking levels. This is due to muscular relaxation and decreased activity of the sympathetic nervous system.
7. Endocrine glands – the secretion of the endocrine glands are the principal regulators of the metabolic rate. The male sex hormones increase the BMR about 10 to 15% and the female sex hormones is little less.
8. Fever – it increases the BMR about 7% for each degree rise in the body temperature above 98.6?F.

Adjustment Of Kcalorie Allowances For Adult Individuals Of Various Body Weights And Ages