Age-related changes in resting energy expenditure in normal weight, overweight and obese men and women

tObjectives: Aging is associated with changes in resting energy expenditure (REE) and body composition.We investigated the association between age and changes in REE in men and women stratified by bodymass index (BMI) categories (normal weight, overweight and obesity). We also examined whether theage-related decline in REE was explained by concomitant changes in body composition and lifestylefactors.Study design: Cross-sectional.Main outcome measures: 3442 adult participants (age range: 18–81 y; men/women: 977/2465) wereincluded. The BMI range was 18.5–60.2 kg/m2. REE was measured by indirect calorimetry in fastingconditions and body composition by bioelectrical impedance. Regression models were used to evalu-ate age-related changes in REE in subjects stratified by sex and BMI. Models were adjusted for bodycomposition (fat mass, fat free mass), smoking, disease count and physical activity.Results: In unadjusted models, the rate of decline in REE was highest in obese men(slope = −8.7 ± 0.8 kcal/day/year) whereas the lowest rate of decline was observed in normal weightwomen (−2.9 ± 0.3 kcal/day/year). Gender differences were observed for the age of onset of REE adaptivechanges (i.e., not accounted by age related changes in body composition and lifestyle factors). In women,adaptive changes appeared to occur in middle-age (∼47 y) across all BMI groups whereas changesseemed to be delayed in obese men (∼54 y) compared to overweight (∼43 y) and normal weight (∼39y) men.Conclusions: Sex and BMI influenced the rate and degree of the age-related decline in REE. Critical agewindows have been identified for the onset of putative mechanisms of energy adaptation. These findingsrequire confirmation in prospective studies.