Basal Metabolic Rate - BMR Calculator

Basal Metabolic Rate - BMR

The Basal Metabolic Rate (BMR) is an index that calculates the amount of energy expended by an organism in a state of total rest, without food consumption and in neutral temperature conditions. Therefore, what it measures is the amount of energy required to keep natural processes running.

The calculation of the Basal Metabolic Rate is taken as a reference on which to work when establishing training and nutrition programs that aim to modify weight or lean mass. Knowledge of this data is what allows us to arrive at others, such as Total Energy Expenditure (TEE), and therefore adjust food intake to achieve the desired effect on the body.

To calculate the Basal Metabolic Rate, a series of equations are performed involving the person's sex, age, weight and height as variables.

There are several formulas used for this purpose. In this calculator you can choose the one you prefer.

The Harris Benedict formula, published in 1919 and later revised in 1984, is the following:

BMR= 88.362 + (13.397 × weight in kg) + (4.799 × height in cm) - (5.677 × age in years) (Men)

BMR= 447.593 + (9.247 × weight in kg) + (3.098 × height in cm) - (4.330 × age in years) (Women)

Based on this formula, which was later revised in 1990, the Mifflin-St Jeor formula was created.

BMR = (10 x weight in kg) + (6.25 x height in cm) - (5 x age in years) + 5 (Men)

BMR = (10 x weight in kg) + (6.25 x height in cm) - (5 x age in years) - 161 (Women)

And finally, another formula, even more accurate, is the Katch-McArdle formula, which is the only one that takes into account the percentage of body fat, and which also works for both sexes. It consists of the following equation:

BMR=370+(21'6 x Lean Mass).

Factors Influencing the calculation of BMR (Basal Metabolic Rate)

should be calculated from time to time in order to have an accurate knowledge of the current reality.

The aspects to be considered that have an impact on BMR are the following:

1. Sex: sex is a conditioning factor, hence there is one formula for men and another for women.
2. Age: age also has an influence, since older individuals need less energy than younger ones. In a certain way, this factor is also linked to the previous one, since muscle development is more pronounced in younger individuals than in older ones, who, due to the decrease in testosterone production that occurs after a certain point in time, find it more complicated to keep muscle mass.
3. Weight and Height: weight and height are used to determine what is known as Body Surface Area, which is a very reliable indicator for measuring metabolism.
4. Muscle Mass: the level of muscle mass is of critical importance in measuring metabolic expenditure. Muscle tissue requires high levels of energy for its maintenance, so considerable muscle development means a higher energy expenditure for the body. This means that an individual who has more muscle mass needs more energy to maintain his body than another whose musculature is less developed.
5. Temperature: External temperature conditions metabolic expenditure, since the organism reacts to temperature variations by making adjustments that allow it to maintain a balance. Thus, if the external temperature is considerably reduced, the body will expend more energy to maintain the body temperature in the range in which it normally is, and the same happens if the external temperature increases excessively.
6. Food - Eating small amounts regularly throughout the day is considered to have some impact on metabolism (but not on BMR, since BMR is calculated in the absence of digestive processes), since it activates the digestion mechanism more frequently, and thus leads to higher energy expenditure. On the other hand, a significant reduction in food intake sustained over time can reduce BMR, because the body interprets that it is in a period of scarcity and therefore minimizes expenditure to ensure survival.

While these are the most important factors, they are not the only ones. Others, such as genetics, pregnancy or the use of stimulant supplements also have an impact on metabolic rate.

To understand the extent to which BMR is important in weight management, it should be noted that of the total daily energy expenditure, about 70% corresponds to what the body needs to maintain its functions at optimal performance. Of the remaining 30%, 20% corresponds to the physical activity performed, and the other 10% to the expenditure produced by digestion.

Reliability of BMR Measurements

With so many elements involved in calculating the Basal Metabolic Rate, the resulting measurements from a calculator should be taken only as a guideline. Even with a controlled environment, where all the variables can be managed, it is not possible to obtain completely accurate results.

In fact, there are still factors at play when calibrating the Basal Metabolic Rate that are not known, and even in very controlled environments a high variability between individuals has been detected.

Therefore, the calculation of the Basal Metabolic Rate should be one more reference on which to work, but taking this indicator with the appropriate reservations.