Resting energy expenditure-fat-free mass relationship: new insights provided by body composition modeling

The relationship between resting energy expenditure (REE) and metabolically active fat-free mass (FFM) is a cornerstone in the study of physiological aspects of body weight regulation and human energy requirements. Important questions, however, remain unanswered regarding the observed linear REE-FFM association in adult humans. This led us to develop a series of REE-body c omposition models that provide insights into the widely used simple linear REE-FFM prediction model derived experimentally in adult humans. The new mo dels suggest that the REE-FFM relationship in mammals as a whole is curvili near, that a segment of this function within a FFM range characteristic of adult humans can be fit with a linear equation almost identical to that obs erved from a composite review of earlier human studies, and that mammals as a whole exhibit a decrease in the proportion of FFM as high metabolic rate organs with greater FFM. The present study thus provides a new approach fo r examining REE-FFM relationships, advances in a quantitative manner previo usly observed albeit incompletely formulated REE-body composition associati ons, and identifies areas in need of additional research.