Aging and energy expenditure

Whether sedentary energy expenditure is normal or lower in elderly people has not yet been clearly established. Twenty-four-hour energy expenditure (24EE) and its different components were measured by use of a respiratory chamber in elderly (17 male, 21 female; 71 ± 6 y, x̄ ± SD; 71.2 ± 13.5 kg; 32 ± 8% fat) and young (33 male, 31 female; 24 ± 4 y; 84.5 ± 23.1 kg; 25 ± 13% fat) subjects. The elderly subjects had lower mean height (P < 0.001), weight (P < 0.01), and fat-free mass (P < 0.001) but higher percent body fat (P < 0.01) than did the young adults. Absolute 24EE, basal metabolic rate (BMR), and sleeping metabolic rate were significantly lower (P < 0.01) in the elderly subjects than in the young subjects. However, after differences in fat-free mass, fat mass, and sex were adjusted for, only BMR was found to be lower in the elderly subjects (P < 0.01). Despite a reduced adjusted BMR in older subjects, sedentary 24EE was decreased only in proportion to their reduced body size, suggesting that the lower energy intake reported in elderly people might be mainly related to lower physical activity in free-living conditions.