Body composition and energy expenditure predict ad-libitum food and macronutrient intake in humans

Abstract

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 (73 females/111 males; age 34.5±8.8 years; percentage body fat: 31.6±8.1%), we investigated the relationship of FFM index (FFMI, kg m(-2)), FM index (FMI, kg m(-2)); and 24-h energy expenditure (EE, n=127) with ad-libitum food intake using a 3-day 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 (%WMENs).

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 are predicted by FFMI and to a lesser degree by FMI. FFM and FM may have opposing effects on energy homeostasis.

Figure 1

Associations of fat-free mass index (FFMI kg*m⁻²), adjusted for age, gender, ethnicity with food and macronutrient intake; CAL, mean daily caloric intake; PRO, mean daily protein intake; CHO, mean daily carbohydrate intake; FAT, mean daily fat intake; %WMEN, percentage weight maintenance energy needs; %PRO, relative caloric contribution of protein; %CHO, relative caloric contribution of carbohydrates; %FAT, relative caloric contribution of fat; r_s indicates Spearman’s ranked correlation. Circles indicate female gender, diamonds indicate male gender.

Figure 2

Associations of fat mass index (FMI kg*m⁻²) adjusted for age, gender and ethnicity with food and macronutrient intake; CAL, mean daily caloric intake; PRO, mean daily protein intake; CHO, mean daily carbohydrate intake; FAT, mean daily fat intake; %WMEN, percentage weight maintenance energy needs; %PRO, relative caloric contribution of protein; %CHO, relative caloric contribution of carbohydrates; %FAT, relative caloric contribution of fat; r_s indicates Spearman’s ranked correlation. Circles indicate female gender, diamonds indicate male gender.

Figure 3

Left column illustrates associations of fat-free mass index (FFMI kg*m^−2,) adjusted for fat mass index, age, gender, and ethnicity with food and macronutrient intake. Right column illustrates associations of fat mass index (FMI kg*m⁻²) adjusted for fat-free mass index, age, gender, ethnicity with food and macronutrient intake; CAL, mean daily caloric intake; PRO, mean daily protein intake; CHO, mean daily carbohydrate intake; FAT, mean daily fat intake; %WMEN, percentage weight maintenance energy needs; r_s indicates Spearman’s ranked correlation coefficient. Circles indicate female gender, diamonds indicate male gender.

Figure 4

Left column illustrates associations of total 24h energy expenditure (24h EE) with mean daily caloric intake (CAL) and overconsumption (%WMEN, percentage weight maintenance energy needs). Right column illustrates associations of 24h EE adjusted for age, gender, ethnicity, fat-free mass and fat mass (i.e. unexplained variance of 24h EE) with CAL and %WMEN. Circles indicate female gender, diamonds indicate male gender. * p values and correlation coefficients were calculated accounting for physical activity.