The basal metabolic rate (BMR) formula is one of the most useful in nutrition. It allows estimating the amount of energy at rest and what foods a person’s metabolism needs per day.
While basal metabolic rate is challenging to change, knowing how much your metabolism is expending per day can help you stay at an ideal weight.
This article discusses the formula to calculate the basal metabolic rate with examples and what it is for.
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Basal Metabolic Rate: What is it, and how to calculate it?
The metabolic rate is the number of calories that a person spends in the day.
The basal metabolic rate or BMR is this figure in the basal state, that is, without moving. The WHO has published articles to calculate how much your metabolism uses.
The key factors that affect basal metabolic rate are gender, age, height, and weight.
There are several methods for calculating your basal metabolic rate. The best known are the Harris-Benedict formula and standardized tables.
While calculating the metabolic rate with the formula is entirely accurate. It is estimated that in practice, this value can vary by up to 10%. The approximate error with this method is about 200-300 kcal.
Calculating the BMR serves as the first step in both losing weight and gaining muscle mass. It is who will determine the calories you should eat per day.
The formula for calculating the basal metabolic rate – TMB
Anthropologists James Arthur Harris and Francis Gano Benedict determined the first formula to calculate the metabolic rate. To arrive at the procedure, the scientists examined 239 subjects of different sexes and ages with varying body fat percentages.
Its formula is the best known and is the one that has been used the longest.
Today, the Harris Benedict basal metabolic rate formulas have been reviewed and updated by international organizations such as FAO and WHO (1,2).
In updating this formula, the coefficient of physical activity was corrected.
The formula for calculating basal metabolic rate according to Harris is:
For men: TMB = 66.47 + (13.75 x weight, kg) + (5.00 x height, cm) – (6.77 x age, years)
For women: TMB = 665.1 + (9.56 x weight, kg) + (1.85 x height, cm) – (4.68 x age, years)
With this formula, we have the value of the basal metabolic rate of a person. To determine the actual calorie needs that a person needs, the number obtained in the previous formula must be multiplied by the physical activity coefficient.
Total metabolic rate and coefficient of physical activity
Once the BMR is obtained, you must apply the formula to calculate the total metabolic rate.
After accurately calculating the basal metabolic rate, this figure must be multiplied by a coefficient ranging from 1.2 to 1.9. The final result is the actual metabolic expenditure between 2118 kcal to 3354 kcal per day.
The Harris formula is in the daily activity coefficient, where there was a more significant error in calculating calories. For this reason, FAO and WHO and universities such as Oxford have made modifications to their TMB formula. (1)
The physical activity coefficients are:
- Minimum (sedentary) – 1.2
- Low (light exercise less than three times a week) – 1,375
- Medium (moderate exercise 3-5 times a week) – 1.55
- High level (intense exercise at least five times a week) – 1,725
- Very high (exercise every day more than once) – 1.9
Examples of calorie calculations from metabolic rate
Here are some examples of calculating your basal metabolic rate using the Harrison-Benedict formula:
- 25-year-old man, height 178 centimeters, weight 72 kilograms, he plays sports three times a week, the rest of the days he works in the office:
BMR = 66.47 + (13.75 x 72) + (5.00 x 178) – (-6.77 x 25) = 1765 kcal
Amount of calories you need = BMR x physical activity coefficient = 1765 x 1.55 = 2735 kcal
- 25-year-old woman, height 172 centimeters, weight 50 kilograms, exercises four times a week, leads an active lifestyle, most of the day on the move:
BMR = 665.1 + (9.56 x 50) + (1.85 x 172) – (4.68 x 25) = 1333
Amount of calories you need = BMR x coefficient of physical activity = 1333 x 1.725 = 2299 kcal
Calorie tables according to metabolic rate by sex and age.
To avoid calculating your basal metabolic rate every time, there are default tables that make this easy. However, it should be understood that these values are approximate.
For example, not every day will you move in the same way. In nutrition, the formula for the basal metabolic rate is used to get a general overview of the situation.
Tables for calculating calories needed by sex and age:
Calorie calculation for men :
|Age||Level of physical activity||Calories needed per day|
|17 – 40 years||Low||2400-2600|
|41 – 60 years||Low||2000-2200|
|Over 61 years||Low||2000|
Calorie calculation for women :
|Age||Level of physical activity||Calories needed per day|
|17 – 40 years||Low||1800-2000|
|41 – 60||Low||1600-1800|
|Over 61 years||Low||1600|
Calorie calculation for children :
|Age||Physical activity||Calories needed per day|
|5 – 8 years||Low||1200-1400|
|9 – 11 years||Low||1500-1800|
|12 – 16||Low||1600-1800|
When determining the number of calories from basal metabolic rate tables, the total error does not exceed 10-15% (approximately +/- 400 kcal).
Is the formula used to calculate calories in athletes?
The basal metabolic rate is a method of calculating calories that can be used in the form of tables and in a personalized way. The Harris formula gives an approximate value, so it is not the best option for high performance athletes.
Also, the basal metabolic rate does not consider the effect of genetic predisposition. The number of calories that a person with a tendency to be thin by nature or ectomorph needs will not be the same as that of a muscular ( mesomorphic ) or with a tendency to gain fat. ( endomorph ).
In addition, there are other electronic systems for analyzing the body: electronic impedance, densitometry, etc., that are capable of determining the amounts of calories relatively accurately.
Some methods even take genetic muscle factors into account. (1) In addition to the basal metabolic rate, another factor that you should take into account is to calculate the ideal body fat percentage. The simplest and most widely used method is using a caliper with tables.
The calculation of the basal metabolic rate is a method to determine the daily calories that a person needs at rest.
To determine the real caloric needs, this value must be multiplied by a physical activity coefficient. The main mistake in Harris’s formula was in this number.
In addition, to calculate what your metabolism uses, there are electronic instruments and other more precise methods and formulas.