Monkeying around with calorie restriction: is a calorie a calorie? - Donald Ingram
Dietary caloric restriction (CR) is the only intervention repeatedly demonstrated to retard the onset and incidence of age-related diseases, maintain function, and extend both lifespan and healthspan in mammals. In 70 years of study, such beneficial effects have been demonstrated in rodents and lower animals, but prior to 1987, had never been examined in primates. To determine whether CR might eventually be applied to humans, the NIA initiated a study of CR and aging in nonhuman primates. After 25 years, approximately 150 rhesus monkeys (Macaca mulatta) have been involved in the study, mostly rhesus monkeys aged across their respective lifespans at the time of initiation. Control monkeys received two meals per day of a standardized, natural ingredient diet sufficient to attain apparent satiety, while the CR group received 30% less, adjusted for age and body weight. The diet is supplemented with extra micronutrients such that the only substantive variable is the amount of calories consumed. Results to date indicate that CR animals are healthier than fully-fed counterparts based on reduced incidence of various chronic diseases, exhibit significantly better indices of predisposition to disease (such as lower insulin levels and greater insulin sensitivity, reduced blood lipids and pressure, and elevated HDL), and appear to age at a slower rate, based on a number of hormonal and functional indices, including behavioral performance. In addition, CR rhesus monkeys that were juveniles at the onset of the study showed delayed skeletal and sexual maturation, and CR groups have lower body temperatures than controls. Regarding the health of older monkeys, our results indicate several significant beneficial effects and few negative effects. However, a recent analysis of current mortality data indicated no evidence of improved survival when CR was initiated at younger or older ages, which contrasted with results reported from the University of Wisconsin study of CR in rhesus monkeys. How differences in dietary regime might account for the differences in results will be discussed.