Energy expenditure of adult male rhesus monkeys during the first 30 mo of dietary restriction.

Energy expenditure, activity, and body composition were measured in 30 adult male rhesus monkeys used in a study having the long-term goal of determining the effects of moderate dietary restriction (DR) on aging. All animals were fed a defined diet, with the restricted animals maintained at approximately 70% of the caloric intakes of the controls. After 12 mo of DR, body fat mass of restricted monkeys was 33% less than that of controls (P = 0.004), whereas lean body mass differences were not present until after 24 mo. At the 24- and 30-mo assessments, nighttime energy expenditure was significantly reduced (P < 0.01) in the restricted compared with control monkeys after adjustment for lean body mass differences, whereas morning, afternoon, and total energy expenditure were not significantly different (P > 0.05). No significant differences (P > 0.05) in activity were noticed between treatment groups at any time point. DR resulted in a prolonged decrease in resting energy expenditure, which could contribute to the possible life-extending action of this treatment.