Body mass index and nutritional status: the effect of adjusting body mass index for the relative sitting height on estimates of the prevalence of chronic energy deficiency, overweight and obesity.

Low body mass index (BMI) has been proposed as a practical measure of adult chronic energy deficiency (CED), although it was well-known limitations. One of these is that its interpretation is complicated by the influence of body proportions, in particular the relative leg length. This has been quantified by examining data collected before 1970 of 349 adult Australian Aborigines following a largely traditional way of life. These Australian Aborigines exhibited low sitting height: stature ratios (SH/S), 0.48± 0.02, (mean ± sd), range 0.41-0.54, ie they are relatively long legged, and low BMI, 19.9± 3.2, range 12-30 kg/m2. Thirty percent of individuals had BMI less than 18.5 kg/m2, a suggested cut-off for CED. The regression of BMI on SH/S was determined in men and women separately but found by covariance analysis not to be different and a common equation for both sexes was calculated. When BMIs were standardized to a SH/S of 0.52, a value found in Europeans and other Indo-Mediterraneans, the percentage classed as chronically energy-deficient fell to 7%. In Asians and indigenous Americans with their high SH/S, the percentage of the population with overweight and obesity could be overestimated and the extent of CED underestimated. In populations with a mean SH/S of 0.52, such as Europeans and Pacific peoples, standardizing SH/S to 0.52 would not effect the prevalence of CED or overweight and obesity but could move individuals across diagnostic boundaries as there is variability in SH/S in all population groups. In conclusion, when using BMI to assess energy nutritional status single cut-offs are not applicable to all individuals and population groups without allowance for the body form and type.