Regulation of body composition during weight recovery: Integrating the control of energy partitioning and thermogenesis

Studies of experimental starvation that were carried out in healthy volunteers during the first half of this century often provide an invaluable source of 'untapped' data. The motivation and desire to gain a better insight into the regulation of body composition by re-analysing these data in the light of more 'modern' concepts of energy partitioning and thermogenesis become irresistible when similar studies can no longer be performed in humans, if only for ethical reasons. This paper brings together new findings, largely centered upon recent re-analysis of data from the classical studies of experimental starvation, semi-starvation and refeeding, and proposes a theory of regulation of body composition during weight recovery in which the cardinal features rest upon three auto-regulatory control systems. These control systems - operating via energy partitioning and two distinct forms of adaptive thermogenesis - have been integrated into a compartmental model for the autoregulation of body composition during cycles of underfeeding/refeeding. This model can be used to explain the individual pattern of lean and fat tissue deposition during weight recovery in situations ranging from rehabilitation after malnutrition/cachexia to the relapse of obesity. It also provides a framework of 'system physiology' for integrating the advances in molecular biology into this area of nutritional energetics.