BMI - Not Necessarily the Best Measure

We’ve urged, and been urged, the need to calculate the BMI to give a ‘better’ reading of overweight and obesity that just the poundage. And we’ve been persuaded that waist girth is sometimes a better predictor of trouble than either of these. Nevertheless, clinical studies usually classify their subjects by BMI: 20-25 is normal, 25-30 is overweight, 30-35 is obese, and so on. For those of us who have a BMI of 26 and are unhappy being considered overweight, help is at hand.

A meta-analysis of 40 clinical studies has been reported in the medical journal Lancet. The analysis covered 250,000 patients with coronary heart disease over a 3½ year period. Results showed that total and cardiovascular mortality were, in fact, better for overweight and mildly obese groups, compared with ‘normal’ BMI patients. How to explain this?

It seems that the BMI fails to discriminate between body fat and lean mass. The better outcome for overweight people is probably because they have more muscle than normal-weight people (which makes me feel a lot better). Since abdominal adiposity, or central obesity, poses a clear risk for cardiovascular disease, the use of the tape measure may indeed be the best solution. And preventive measures should concentrate on a reduction in body fat, rather than simple weight loss. But this is really a change in what you measure, not what you do – you must still exercise a lot and avoid saturated fats, trans fats, and too many calories. Meanwhile, don’t expect clinical studies to switch from BMI values to pounds (or kilograms) or even percentage body fat. It will take time for this new concept to be digested and accepted by the clinicians before they adapt their protocols accordingly.