One reason why waist-to-height ratio is usually better related to chronic disease risk and outcome than body mass index.

The waist-to-height ratio (wtHR) has been proposed as an alternative to body mass index (BMI) as a simple anthropometric measure of body fatness. Both measures retain residual correlations with height, which causes them to over- or under-adjust for height (and thus misestimate nutritional state) when relating these measures to chronic disease risk, morbidity or mortality. The possibility that BMI has greater misadjustment than wtHR relative to waist/height (p) and weight/height (p) (where p is the optimal exponent for each population and sex group) is examined here. Analysis of anthropometric data for groups in Thailand, Papua New Guinea and Australia shows that this is the case, especially over-adjustment. This may contribute to the weaker relationships of chronic disease markers and outcomes with BMI than with wtHR.