Sex Differences in Measures of Energy Expenditure and Body Composition in Young, Middle-Aged, and Older Adults

Total daily energy expenditure (TDEE) is vital for energy balance and cardiometabolic health, yet its trajectory across the lifespan, particularly in females, remains poorly understood.

We sought to examine the effects of aging and sex on body composition and TDEE.

In a cross-sectional analysis of data from research centers across 9 European Countries and the United States from the International Atomic Energy Agency database, TDEE and body composition measures of 2326 participants (1560W/766M; 50.7 ± 12 .6 y) were stratified across age groups: young (30-39 y; YOUNG), middle-aged (40-54 y; MID), and old (55-70 y; OLD). Doubly labeled water was used to estimate TDEE and fat-free mass (FFM). Fat mass (FM) was calculated as the difference between body mass and FFM, and %fat was ratio between FM and body mass as a percentage. Linear models were used for analysis.

Females demonstrated greater FM and lower FFM with each age group, compared with males (P < 0.001). In females, OLD had lower absolute TDEE than YOUNG (-217 kcal/d, P < 0.001) and MID (-208 kcal/d, P < 0.001). Male absolute TDEE was lowered across all age groups (OLD compared with YOUNG: -334 kcal/d; OLD compared with MID: -210 kcal/d; MID compared with YOUNG: -124 kcal/d; P < 0.001). Adjusted TDEE was similar within age groups between females and males.

These results suggest that age influences changes in body composition and energy expenditure similarly between males and females. The most significant change in TDEE occurs as individuals transition from middle age to older adulthood. Females generally have a higher percentage of %fat and FM, along with lower FFM, compared with males across all age groups. These findings are important for understanding how aging affects metabolism and body composition, which could inform sex-specific health strategies and interventions.