The body mass index (BMI) is an international standard recognized by the World Health Organization (WHO) for calculating a person's body mass, that is, the distribution of his weight concerning his height.

With BMI, it is possible to tell whether a person is overweight, or, on the contrary, is too skinny. This index can therefore detect possible health risks due to the body size of a person.

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What is body mass index (BMI)?

The body mass index (BMI) makes it possible to calculate very precisely the body size of a person, that is, his height, overweight, obesity, or thinness. BMI is a more accurate indicator than weight because the same weight in different people does not necessarily correspond to obesity or thinness in these same people. The size indeed specifies their general corpulence. BMI can detect excess fat mass that can have negative health consequences.

The formula for calculating BMI for an adult woman or man (18-65 years) is the weight (kg) / Size2 (m). The obtained result determines the level of corpulence :
  • over 40 = morbid or massive obesity
  • 35 to 40 = severe obesity
  • 30 to 35 = moderate obesity
  • from 25 to 30 = overweight
  • 18.5 to 25 = normal body size
  • from 16.5 to 18.5 = thinness
  • less than 16.5 = undernutrition
For children aged 2 to 18 years, the result of the body mass index (BMI) is not interpreted as that of adults and varies between the sexes, while the calculation formula is the same. BMI is reported in the child's Health Record on what is called a" corpulence curve " whose unit is the percentile. When the BMI is above the 97th percentile, the child is considered obese. If it is less than the 3rd percentile, the child is underweight.

What is the body mass index (BMI) for?

BMI indicates, in particular to health professionals, an estimate of a person's body fat and therefore the health risks associated with corpulence. Most importantly, BMI is used to estimate the risk of diseases, including those related to overweight such as heart disease, high blood pressure, Type 2 diabetes, gallstones, respiratory problems, and certain types of cancer.

The Body Mass Index is a simple tool, which does not require spending to implement it, and it is the best indicator for measuring overweight and obesity, factors of many diseases. For example, a BMI above 30 indicates an increased risk of cancer, joint problems, infertility, and mortality. At this level, it is estimated that life expectancy can be reduced from 2 to 4 years. BMI makes it easy to identify people at risk and track them and help them lose weight for their health.

Limits of body mass index (BMI)

Like any indicator, BMI knows limits. Indeed, it does not apply to everyone in the same way. For example, it has been shown that the interpretation of BMI in terms of health risks is not the same for people 65 years of age and older. Similarly, BMI is not recommended for pregnant or breastfeeding women. Weight gain during pregnancy is necessarily assessed based on the body size of the woman at the outset, and not on a population-wide standard such as Body Mass Index.