Operation Manual

12
Body weight / Body mass index
The body mass index (BMI) is a number that is often called upon to evaluate body weight. The number is
calculated from body weight and height, the formula is – body mass index = body weight : height². The
measurement unit for BMI is [kg/m²].
Man < 20 years Woman < 20 years
Age Under-
weight
Normal weight Over-
weight
Age Under-
weight
Normal weight Over-
weight
10 12,7 – 14,8 14,9 –18,4 18,5 – 26,1 10 12,7 – 14,7 14,8 –18,9 19,0 – 28,4
11 13,0 – 15,2 15,3 –19,1 19,2 – 28,0 11 13,0 – 15,2 15,3 –19,8 19,9 – 30,2
12 13,3 – 15,7 15,8 –19,8 19,9 – 30,0 12 13,3 – 15,9 16,0 – 20,7 20,8 – 31,9
13 13,7 – 16,3 16,4 – 20,7 20,8 – 31,7 13 13,7 – 16,5 16,6 – 21,7 21,8 – 33,4
14 14,2 – 16,9 17,0 – 21,7 21,8 – 33,1 14 14,2 – 17,1 17,2 – 22,6 22,7 – 34,7
15 14,6 – 17,5 17,6 – 22,6 22,7 – 34,1 15 14,6 – 17,7 17,8 – 23,4 23,5 – 35,5
16 15,0 – 18,1 18,2 – 23,4 23,5 – 34,8 16 15,0 – 18,1 18,2 – 24,0 24,1 – 36,1
17 15,3 – 18,7 18,8 – 24,2 24,3 – 35,2 17 15,3 – 18,3 18,4 – 24,4 24,5 – 36,3
18 15,6 – 19,1 19,2 – 24,8 24,9 – 35,4 18 15,6 – 18,5 18,6 – 24,7 24,8 – 36,3
19 15,8 – 19,5 19,6 – 25,3 25,4 – 35,5 19 15,8 – 18,6 18,7 – 24,9 25,0 – 36,2
Man / Woman ≥ 20 years
Age Under-
weight
Normal weight Over-
weight
≥ 20 15,9 – 18,4 18,5 – 24,9 25,0 – 40,0
Source: Bulletin of the World Health Organization 2007;85:660-7; Adapted from WHO 1995, WHO 2000 and WHO 2004.
Note that with very muscular physiques (body builders), the BMI interpretation will show overweight.
The reason for this is that no account is taken of well above average muscle mass in the BMI formula.
Results in relation to time
Note that it is only the long-term trend which counts. Short period fluctuations in weight over a few days
are mostly the result of a loss of fluid.
The interpretation of the results will depend on changes in your: overall weight and body fat, body water
and muscle percentages, as well as on the period during which these changes take place. Rapid changes
within days must be distinguished from medium term changes (over weeks) and long term changes
(months).
A basic rule is that short term changes in weight almost exclusively represent changes in water content,
whereas medium and long term changes may also involve the fat and muscle percentages.
• If your weight reduces over the short term, but your body fat percentage increases or remains the same,
you have merely lost water – e.g. after a training session, sauna session or a diet restricted only to rapid
weight loss.
• If your weight increases over the medium term and the body fat percentage falls or stays the same, then
you could have built up valuable muscle mass.
If your weight and body fat percentage fall simultaneously then your diet is working – you are losing fat
mass. Ideally you should support your diet with physical activity, fitness or power training. By this means,
you can increase your muscle percentage over the medium term.