Influence of fat-free mass and resting metabolic rate on increased food reinforcement after exercise training

Purpose Models of appetite control have been largely based on negative feedback from gut and adipose signaling to central appetite centers. However, contemporary models posit that fat-free mass (FFM) or the energy demand of FFM [i.e., resting metabolic rate (RMR)] may play a primary role in the motivational drive for food intake (i.e., food reinforcement). The relative reinforcing value of food (RRVfood) is associated with energy intake (EI) and increases with an acute energy deficit. Chronic exercise-induced energy deficits lead to alterations in fat mass (FM), FFM, and RMR and provide an opportunity to test whether change in ( increment ) FM, increment FFM, increment usual EI, or increment RMR are associated with increment RRVfood. Methods Participants (n = 29, BMI = 25-35 kg/m(2)) engaged in aerobic exercise expending 300 or 600 kcal, 5 days/weeks for 12 weeks. The reinforcing value of food (PMax(food)) was measured via a computer-based operant responding task and RRVfood was calculated as the reinforcing value of food relative to non-eating sedentary behaviors. RMR was determined by indirect calorimetry and body composition by DXA. Results Post-training FFM correlated with usual post-training EI (r(s) = 0.41, p < 0.05), PMax(food) (r(s=)0.52, p < 0.01), and RMR (r(s) = 0.85, p < 0.0001). increment RMR negatively correlated with increment PMax(food) (r(s) = - 0.38, p < 0.05) and with increment RRVfood (r(s) = - 0.37, p < 0.05). increment PMax(food) and increment RRVfood were not associated with increment FFM (p = 0.71, p = 0.57, respectively). Conclusions Reductions in RMR with weight loss may increase food reinforcement as means of restoring FFM and RMR to pre-weight loss amounts. Limiting reductions in RMR during weight loss may benefit weight maintenance by restricting increases in food reinforcement after weight loss.