Fat-Free Mass (FFM) settling point regulation of energy partitioning and energy intake

We constructed a computer simulation model of human body composition, with energy partitioning dependent upon a "FFM Settling Point". In contrast to previous models, the FFM Settling Point Model allows fat and FFM to change in parallel or opposite directions. We calculated FFM Settling Point from energy balance and the hypertrophic effect of exercise, which we derived from published experimental data. The hypertrophic effect of exercise was found to be greater in males, and is the major gender-specific model parameter. We found the best fit to experimental data when the hypertrophic effect of exercise made up about 80% of the FFM Settling Point. This optimal weighting of the energy balance and hypertrophy components of the FFM Settling Point did not appear to be correlated to the type of experimental regimen or to gender. We found that, for a variety of protocols, simulated changes in fat and FFM were within one standard deviation (when reported) of the experimental mean. We also found that for a given energy intake and protocol duration, the model predicts a bimodal curve for FFM vs. Exercise. This may explain discrepant experimental findings in the response of FFM to diet combined with exercise. We also hypothesized that energy intake may be influenced by the FFM Settling Point. When we modeled energy intake as a function of FFM Settling Point, we found a bimodal relationship between energy intake and exercise, as reported in the classic studies of Mayer et al.(1954,1956).