Adaptive reduction in basal metabolic rate in response to food deprivation in humans: a role for feedback signals from fat stores

We assessed the importance of lean and fat tissue depletion as determinants of the adaptive reduction in basal metabolic rate (BMR) in response to food deprivation by reanalyzing the data on BMR and body composition for the 32 men participating in the classic Minnesota experiment of semistarvation and refeeding. We used individual data on BMR, body fat, and fat-free mass (FFM) assessed during the control (prestarvation) period, at weeks 12 and 24 of semistarvation (S12 and S24), and week 12 of restricted refeeding (R12) to calculate an index of the reduction in thermogenesis at S12, S24, and R12, defined as the change in BMR adjusted for changes in FFM and fat mass, and an index of the state of depletion of the fat mass and FFM compartments at these times, defined as the deviation in fat mass or FFM relative to control values. The results indicated a positive relation between the reduction in thermogenesis and the degree of fat mass depletion (but not FFM depletion) during weight loss as well as during weight recovery (r = 0.5, P < 0.01). Furthermore, the residual variance was predicted by the initial (prestarvation) percentage fat and the cormic index (sitting height/height). Taken together, these results in normal-weight men responding to severe food deprivation reveal anthropometric predictors for human interindividual variability in the capacity for energy conservation and suggest that the adaptive reduction in BMR is partly determined by an autoregulatory feedback control system linking the state of depletion of fat stores to compensatory mechanisms that suppress thermogenesis.