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As a nurse working in coronary care, I am naturally concerned about
obesity and its effects on health. However, I wonder if we are using the
correct measure of obesity when we use the body mass index.
As it is currently calculated by dividing the weight of person by
the square of his/her height, it assumes that the two are proportional. I
have not been able to find any evidence or papers to show this to be the
case. In fact, logic suggests that weight will be proportional to volume,
which relates to the cube of height in a normally proportioned person, not
Thus, if two people of 1.7 metres and 1.9 metres tall respectively
have similar proportions and the former weighs 80 kg, then the latter
could be expected to weigh about 112 kg. Using the present method of
calculation, the shorter would have a body mass index of 27.7, in the
middle of the overweight range. However, the taller would have a body
mass index of nearly 31, and thus would be classified as obese.
Could it be the part of the present claimed increase in obesity is,
in fact, simply an increase in height?
I suggest that we need a new body mass index which relates to the
cube of height, or use the simple measure of girth divided by height.