Body Composition and Energy Expenditure Predict Ad-Libitum Food and Macronutrient Intake in Humans

BACKGROUND: Obesity is the result of chronic positive energy balance. The mechanisms underlying the regulation of energy homeostasis and food intake are not understood. Despite large increases in fat mass (FM), recent evidence indicates that fat-free mass (FFM) rather than FM is positively associated with intake in humans. METHODS: In 184 humans (73F/111M; age 34.5±8.8y; % body fat [PFAT] 31.6±8.1%) we investigated the relationship of FFM index (FFMI kg*m(2)), FM index (FMI kg*m(2);), and 24-hour energy expenditure (EE, n=127) with ad-libitum food intake using a 3d vending machine paradigm. Mean daily calories (CAL), and macronutrient intake (PRO, CHO, FAT) were determined and used to calculate the relative caloric contribution of each (%PRO, %CHO, %FAT) and percent of caloric intake over weight maintaining energy needs (%WMEN). RESULTS: FFMI was positively associated with CAL (p<0.0001), PRO (p=0.0001), CHO (p=0.0075), and FAT (p<0.0001). This remained significant after adjusting for FMI. Total EE predicted CAL and macronutrient intake (all p<0.0001). FMI was positively associated with CAL (p=0.019), PRO (p=0.025) and FAT (p=0.0008). In models with both FFMI and FMI, FMI was negatively associated with CAL (p=0.019) and PRO (p=0.033). Both FFMI and FMI were negatively associated with %CHO and positively associated with %FAT (all p<0.001). EE and FFMI (adjusted for FMI) were positively (EE p=0.0085; FFMI p=0.0018) and FMI negatively (p=0.0018; adjusted for FFMI) associated with %WMEN. CONCLUSION: Food and macronutrient intake is predicted by FFMI and to a lesser degree by FMI. FFM and FM may have opposing effects on energy homeostasis.