Obesity is associated with numerous chronic conditions diseases. A healthy lifestyle, with a balanced diet and the regular practice of a physical activity, help to prevent weight gain and the many related complications.

Calculation of the BMI

The Body Mass Index (BMI) is a measurement frequently used to estimate underweight or overweight.

The BMI establishes the height-weight ratio by dividing the weight in kilograms by the square of the height in metres (kg/m²).

BMI classification (WHO) :

  • undernourishment : < 16.5
  • underweight : 16.5-18.4
  • normal weight : 18.5-24.9
  • overweight (pre-obsese) : 25.0-29.9
  • moderate obesity (class I) : 30.0-34.9
  • severe obesity (class II) : 35.0-39.9
  • very severe obesity (class III) : ≥ 40

N.B.! The classification of obesity in accordance with the BMI does not apply to people under the age of 18 years or to pregnant women. Nor does the BMI make it possible to assess the quantity of fat or its distribution in the body. The place where the fat accumulates, however, is an important indicator when it comes to assessing possible complications.

Waist circumference

The waist circumference measurement and the waist-to-hip ratio make it also possible to estimate overweight, with the advantage of being able to define where the fat is localised.

An accumulation of fat around the waistline multiplies the risk of diabetes and cardiovascular diseases.

In women:

  • waist circumference between 80 and 88 cm: increased risk
  • greater than 88 cm: very serious health risk.

In men:

  • waist circumferencebetween 94 and 102 cm: increased risk
  • greater than 102 cm: very serious health risk.

History taking and supplementary examinations

During a consultation, the doctor may ask personal questions concerning:

  • the development of weight gain (beginning, periods of stability and relapse)
  • the family, professional or emotional context which might lead to weight gain
  • diets undertaken
  • eating habits
  • physical activities.

A blood sample will make it possible to verify the sugar, fat and cholesterol levels and help in determining if the overweight is accompanied by a risk of diabetes or cardiovascular diseases.

In its population surveys, Sciensano investigates the problem of obesity by analysing the practice of physical activities, the Body Mass Index (BMI) and the dietary habits of the population. 

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