BASAL METABOLIC RATE - BMR

            
      Basal metabolism or basal metabolic rate (BMR) is defined as the minimum amount of energy required by the body to maintain life at complete physical and mental rest in the post-absorptive state (i.e. 12 hours after the last meal). 

            Under the basal conditions, although the body appears to be at total rest, several functions within the body continuously occur. These include working of heart and other organs, conduction of nerve impulse, re-absorption by renal tubules, gastrointestinal motility etc. 

Units of BMR: BMR is expressed as Calories per square meter of body surface area per hour i.e. Cal/sq.m/hr. 

Normal Values of BMR:

 For adult man 35-38 Cal/sq.m/hr;

           For adult women 32-35 Cal/sq.m/hr. 

For an adult man BMR is around 1,600 Cal/day, while for an adult woman it is around 1,400 Cal/day. 

FACTORS AFFECTING BMR

1. Surface area: It is related to weight and height
2. Sex: Men have marginally higher (about 5%) BMR than women. This is due to the higher proportion of lean muscle mass in men.
3. Age: In infants and growing children, with lean muscle mass, the BMR is higher. In adults, BMR decreases at the rate of about 2% per decade of life.
4. Physical activity: BMR is increased in persons with regular exercise.
5. Hormones: Thyroid hormones have a stimulatory effect on the metabolism of the body, and therefore BMR. Thus, BMR is raised in hyperthyroidism and reduced in hypothyroidism.
6. Environment: In cold climates, the BMR is higher compared to warm climates
7. Starvation: During periods of starvation, the energy intake has an inverse relation with BMR, a decrease upto 50% has been reported.
8. Fever: Fever causes an increase in BMR. An elevtion by more than 10% in BMR is observed for every 1⁰C rise in body temperature.
9. Disease status: BMR is elevated in various infections, leukemias, polycythemia, cardiac failure, hypertension etc.

SIGNIFICANCE OF BMR

            BMR is important to calculate the calorie requirement of an individual and planning of diets. Determination of BMR is useful for the assessment of thyroid function. 

DAILY ENERGY NEEDS

•   Resting metabolic rate (RMR): The amount of energy expended while at rest; represents the minimal amount of energy required to sustain vital bodily functions such as blood circulation, respiration, and temperature regulation. RMR typically accounts for 70% of Total energy expenditure (TEE).

ESTIMATING TOTAL DAILY ENERGY EXPENDITURE

            One of the most common ways to estimate TEE is to first estimate RMR, and then multiply RMR by an appropriate activity factor. One of the simple equations to estimate RMR is as follows:

Step  1.  Weight (lbs) x 10 = RMR

Step 2.  RMR X activity factor (check the table below) = TEE

Eg: Heavily active 180-pound man

·         Step 1. 180 lbs x 10 = 1800 RMR

·         Step 2. 1800 RMR x 2.1 activity factor = 3780 calories expended per day (i.e. TEE)

Table: physical activity factors for various levels of activity for adults of average size 19 years or older: 

Very light	Seated and standing activities, office work, driving, cooking; no vigorous activity	1.2 - 1.3
Low active	In addition to the activities of a sedentary lifestyle, 30 mins of moderate activity equivalent of walking 2 miles in 30mins, most office workers with additional planned exercise routines	1.5 – 1.6
Active	In addition to the activities of a low active lifestyle, an additional 3 hours of activity such as bicycle 10-12 miles an hour, walk 4.5 miles an hour	1.6 – 1.7
heavy	Planned vigorous activities, physical labour, full-time athletes, hard-labour professionals such as steel or road workers	1.9 – 2.1

             The formular can have a variance up to 20% in overestimating or underestimating resting metabolism and total energy expenditure. 

              Moreover, it is important to note that calorie requirements change with life stage, activity level, and illness. Proper weight management for most individuals should include regualarly monitoring weight status with weekly or monthly weight-ins or body composition assessments. In doing so any unwanted weight gain can immediately be immediately addressed, which consequently prevents creeping obesity and related health complications. 

REFERENCES
 

1.      Biochemistry: Dr. U. Satyanarayana – 2^nd edition

2.      NASM Essentials of  personal fitness training – 4^th Edition