All about the body mass index and the percentage of fat


The evaluation of body composition is an indispensable element to determine the health of the people and thus be able to formulate nutritional recommendations and exercise prescriptions.

It is also used to control the growth of children and adolescents, the changes produced by aging, the body weight of athletes involved in weight-regulating competitions, etcetera. But two of the most studied aspects concerning the evaluation of the body composition are the percentage of fat and the body mass index.

They are two different elements that in some cases relate and in others not. Next we will see what each one is and the appropriate values of the body composition for each one of them.

Percentage of body fat

This concept differs from BMI, it’s not the same. To classify the lipid level of our organism we use relative body fat (% GC). The body composition differs between fat and fat-free dough (muscles, bones, etc.). This percentage measures only measures the percentage of fat by despising the fat-free mass.

To calculate it there are many methods,simple imc online for example) the vast majority indirect because it is very difficult to know the exact content of body fat. One of the most effective and precise forms is through Dexa technology, an expensive material and only available in hospitals. However, there are other methods that are much more affordable and also reliable as the anthropometry with Plicometros.

Usually there is a relationship between the% of body fat and BMI. If there is a high body mass index is because there is a large amount of body fat, except for the case of athletes. To have an orientation on the appropriate levels we attach a useful table.

Body Mass Index

BMI is the relationship between weight and size and is used to identify overweight and obesity in adults, as long as it is done properly. It is calculated by dividing the weight in kilograms by the square of the size in meters – weight (kg)/size (m2).

A simple example: a person with 90 kilograms of weight and a height of 1.70 will have a body mass index of 31.4, which would place him in type I obesity. For a person of 1.70 of height the classification would be like this:

It is the most useful measure to measure the overweight and obesisdad of the population, since their calculation is always the same, regardless of the sex or age of the adult. However, it should only be treated as something approximate because it does not always correspond to the same degree of fatness in individuals.

The World Health Organization establishes overweight as a BMI equal to or greater than 25, while obesity would be a BMI equal to or greater than 30. These are the two most important thresholds, although there are many subdivisions:

However, when evaluating the body composition of athletes the body mass index is practically useless, and this is because it only contemplates the weight, regardless of whether that weight is mostly muscle mass or fat.

An athlete who measures 1.77 and has a weight of 88 kilograms, will have a BMI of 28.09 which would suppose that would be within the calisifcación of overweight grade II, also called preobesity. And probably this athlete has a percentage of body fat less than 10%, therefore the measure of BMI in this case is completely invalid.


May Capobianco