BMI what is it ?
Authors: Eva Heinen, graduate sports scientist (Univ), Prof. Dr. med. Edgar Heinen
The Body Mass Index (BMI) is calculated by dividing the body weight in kg by the square of the height in meters. The resulting value shows no correlation with height in men. In women, however, there is a small but significant negative correlation between body weight and BMI. Overall, however, the body weight of people of different heights can be compared with each other, a necessary prerequisite for all scientific studies on body weight and obesity.
But what is the BMI supposed to mean?
why can this work better than, for example, the kg to body surface area value?
If you look at the formula and consider that 1 kg of body mass corresponds almost exactly to 1 l of distilled water (for the deviations of the specific weight from 1, see measurement of body composition ), then 70 kg of body weight corresponds to a volume of 70 l or 70 dm³ or 0.070 m³. This size divided by the body height squared results in a value of 0.0229 m or 22.9 mm for a body height of 1.75 m (see figure above). Mathematically, the BMI therefore represents the height of the water level (in mm) if you pour as many liters of water as your body weight in kg into a square container with a side length equal to your height.
Calculate your BMI:
A person weighing 70 kg with a height of 1.75 m has a BMI of 70 / 1.75 /1.75 = 22.9 kg / m².
The World Health Organization assesses a person’s nutritional status using BMI according to the criteria shown in the table.
But what does it mean for you if you should achieve a BMI of less than 25 kg/m², how much can you then weigh?
Calculate the weight that you would have to reach at your height in order to achieve your desired BMI:
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Simply use the formula: desired BMI x height x height (each in m);
e.g: Desired BMI less than 25 kg/m², with a height of 1.75 m desired:
25 kg/m² / 1.76 m / 1.75 m = 76.5 kg. You should therefore weigh less than 76.5 kg with a height of 1.75 m.
For the limitations of using BMI as a measure of obesity, see the Body Composition chapter