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Basal Metabolic Rate (BMR) Calculation and its Applications

The Basal Metabolic Rate (BMR) is the number of calories you would burn per day if you did nothing all day. To lose weight, you should burn off more calories than you ingest. You can burn off calories by doing any type of activity (physical or mental) and you will actually burn off calories naturally just by doing nothing, even when asleep. Knowing your basal metabolic rate will help you determine how many calories you can consume per day without gaining weight even if you stayed in bed all day long. Depending on your activity level, your basal metabolic rate makes up 60-75% of the calories expended each day. Hence, if you wish to lose weight and you have a sedentary lifestyle, you should reduce your daily calorific intake below your basal metabolic rate.

However, you should remember that starving yourself with harsh diets can slow down your metabolism and thus lower you basal metabolic rate. So do not overdo it. This happens because when starving yourself you lose muscle mass before you lose fat and your body will thus burn less calories naturally. Your body does not realize that you are on a diet, it will think you are actually starving and will try to preserve as much weight and fat as possible. Conversely, you can increase your basal metabolic rate by building up muscle mass but do not panic when on the scale because muscle weighs more than fat. So keep in mind that the rate at which your body burns calories (metabolic rate) and your overall body composition (e.g., how much muscle you have in relation to body fat) plays a significant role in managing your overall weight.

Although the basal metabolic rate (BMR) can be measured by calorimetry, it is more convenient and very common to estimate it using a formula with variables such as person’s weight, height, age and gender. There are different formulae for men and women because female body typically contains a higher percentage of fat. Age, on the other hand, needs to be taken into account too, because as we age, our metabolic rate slows.

BMR estimation formulae:

Male BMR = 66.5 + (13.7 × Weight in kilograms) + (5 × Height in centimetres) – (6.8 × Age)

Female BMR = 655 + (9.6 × Weight in kilograms) + (1.8 × Height in centimetres) – (4.7 × Age)

* Please note that when using imperial units, feet need to be entered in decimal points, e.g. 5 foot 11 inch equals 5.9 feet (i.e. 5 + 11/12).

Basal Metabolic Rate vs Resting Metabolic Rate

You may have heard of the resting metabolic rate (RBR) as being synonymous with the basal metabolic rate (BMR). These two terms are often used interchangeably even though there is a small difference between the two. In laboratory testing, the basal metabolic rate is measured after eight hours of sleep and twelve hours of fasting whereas the resting metabolic rate does not require the subject to spend a night in the laboratory or hospital prior to testing. The analysis is otherwise the same. The resting metabolic rate can also be estimated using a formula that is slightly different from the BMR formula. Both types of formulae (BMR and RMR) use the same inputs but results for larger people may differ quite significantly.

RMR estimation formulae:

Male: BMR = 10 × weight + 6.25 × height – 5 × age + 5

Female: BMR = 10 × weight + 6.25 × height – 5 × age – 161

* Please note that when using imperial units, feet need to be entered in decimal points, e.g. 5 foot 11 inch equals 5.9 feet (i.e. 5 + 11/12).

See also: Calculating the Body Mass Index (BMI), Calculating the Body Adiposity Index (BAI) and Estimating the Body Fat Percentage