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 (RRV_food) 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 (∆) FM, ∆FFM, ∆usual EI, or ∆RMR are associated with ∆RRV_food. Methods: Participants (n = 29, BMI = 25–35 kg/m²) 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 RRV_food 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). ∆RMR negatively correlated with ∆PMax_food (r_s = − 0.38, p < 0.05) and with ∆RRV_food (r_s = − 0.37, p < 0.05). ∆PMax_food and ∆RRV_food were not associated with ∆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.