Influences of calorie restriction and age on energy expenditure in the rhesus monkey

Caloric restriction ( CR) is known to retard the aging process, and a marker of aging is decreased energy expenditure ( EE). To assess longitudinal effects of CR on EE in rhesus monkeys ( Macaca mulatta), data from 41 males ( M) and 26 females ( F) subjected to 9 or 15 yr of CR were studied. EE and body composition of monkeys 11 - 28 yr of age were measured using indirect calorimetry and dual X-ray absorptiometry. Total EE ( 24-h EE) was divided into daytime ( day EE), nighttime ( night EE), and daytime minus nighttime ( D - N EE). M calorie-restricted monkeys showed a lower 24-h EE ( means +/- SD = 568 +/- 96 kcal/ day, P < 0.0001) than controls ( C; 630 +/- 129 kcal/ day). Calorie-restricted M had a lower night EE ( difference = 36 kcal P < 0.0001) compared with C M, but after adjusting for FFM and FM, night EE was not different between calorie-restricted and C males ( P = 0.72). The 24-h EE decreased with age ( 13 kcal decrease/yr, P < 0.0001), but there was no difference between CR and C. Adjusted for FFM and FM, D - N EE decreased with age ( 9 kcal/ yr, P < 0.0001), with no interaction with age ( P = 0.72). The F were compared with age-matched M selected from the male cohort. F had a lower 24-h EE ( 496 +/- 84 kcal/ day) than M ( 636 +/- 139 kcal/ day) ( P < 0.0001). Adjusting for FFM and FM, night EE was lower in F compared with M ( difference = 18 kcal, P = 0.077). Night EE did not differ between calorie-restricted and C younger monkeys after adjusting for FFM and FM. In conclusion, CR did not alter the age-related decrease in EE with CR.