This paper suggests the hypothesis that variation in Sitting Height Ratio (SHR) may be a major and easily measurable factor to correct observed bias in mean basal metabolic rates (BMR) predicted from body weight, due to influence of SHR on the share of various body parts in total BMR, for given height, Body Mass Index or weight, affecting in turn estimation of energy needs and undernourishment. A modelling approach is used here to suggest that unexplained discrepancies between predicted and measured mean BMR in different ethnic groups and geographical areas may be due in large part to differences in SHR. This may significantly affect estimates of undernourishment worldwide and in specific countries and populations.