Response

I thank Dr Abrahim for his comments in response to my article “Normal-weight central obesity. Unique hazard of the toxic waist,” published in the June issue of Canadian Family Physician.¹ There is little doubt that waist circumference (WC) should be a very unreliable measurement for the proportion of visceral to subcutaneous (SC) fat, and there is even no universal consensus surrounding where to measure or what the measurement cutoff value for risk should be. In spite of this, the anthropometric measures of abdominal obesity have surprisingly high correlations with mortality. Perhaps if we had simple and reliable ways of measuring only the high-risk visceral component, the association would be even stronger.

Several studies using computed tomography have shown that the ratio of visceral fat to SC fat is an independent predictor of cardiac events and mortality.^2,3 This ratio is likely to be larger in the lean centrally obese than in the globally obese who have a much thicker abdominal SC fat layer, lending some credence to the possibility that SC fat might offer some protection against the ravages wrought by visceral fat.

In lean centrally obese people the SC fat partition would be expected to be a smaller part of the waist circumference component than in the globally obese. It has been shown that, as obesity increases, the infiltration of macrophages and inflammatory activity increases markedly in visceral fat,⁴ perhaps helping to explain why the large contribution of subcutaneous fat to WC measurement does not greatly diminish the value of this metric in predicting cardiometabolic events.

It would seem that no matter how inexact WC measurement is, it consistently identifies mortality risk better than body mass index does. A pragmatic metric such as waist-to-height ratio then allows a busy family physician to flag this risk if WC exceeds half the patient’s height. This is at least equally important if the person is not globally obese.