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On 07-Feb-05 Puliyel wrote: > > Dear Ted > You are correct to conclude that BMI (Weight divided by > square of height ) is not a rational index of obesity. > However your suggestion of using the cube of the height > would make it an even poorer index. > The reason is simple: Suppose a person grows 1 foot taller. > He does not automatically become 1 foot wider and 1 foot > deeper like a cube. If he does, he is obviously getting obese. Dear Jacob, Thank you for the comment. However, I was not proposing that people were cubic in shape, nor grew by equal distances in all directions! My "theoretical" reasoning adopted the premiss that proportion was preserved: width = Cw*height, depth = Cd*height, so that volume (crudely)= height*width*depth = Cw*Cd*(height cubed). Specifically, if someone is 60 inches tall, 20 inches wide (shoulder to shoulder) and 10 inches deep (sternum to scapula) then if that person grew one foot (20%) taller and maintained the proportions, they would be 72 inches tall (12 inches taller), 24 inches wide (4 inches wider) and 12 inches deep (2 inches deeper). Since their shape would not have changed, they would be neither more nor less obese than before. The real point of my theoretical discussion was that if all proportions (proportional volumes, shapes, dispositions) of different tissue types were preserved then there would be no obvious reason to conclude that the healthiness of the second body should be other than identical to the healthiness of the first. But the BMI would have increased by 20 per cent. Hence BMI can fluctuate by a considerable percentage without the slightest implication that there is a body change which might be health related (and remember that e.g. distinctions between "healthy", "overweight" and "obese" correspond to approx. 20% increment of BMI: <=25, 25-30, >30). Best wishes, Ted. -------------------------------------------------------------------- E-Mail: (Ted Harding) <[log in to unmask]> Fax-to-email: +44 (0)870 094 0861 Date: 08-Feb-05 Time: 00:27:10 ------------------------------ XFMail ------------------------------