It has long been observed in the field of ageing research that nonhuman animals on a calorie-restricted diet boast slower metabolisms and live longer than their counterparts who regularly consume more calories. A new study has found “the strongest evidence yet” that the same could be true for humans.
In the 20th century, two theories of ageing were proposed that continue to survive scientific scrutiny today. The first, called the “rate of living” theory, dates back to 1928 and states that life span depends on one’s speed of metabolism relative to body mass. The second, introduced in 1956, is called the “oxidative damage” theory and states that the ageing process is accelerated by a buildup of reactive oxygen species, or “free radicals”, chemical by-products of metabolism that cause damage to cells in the long run.
Calorie restriction (CR) has been shown through many studies to increase the lifespan of many different species (most of which have lives short enough to study), a finding thought to be explained by both these theories. While some studies of CR in nonhuman primates have shown promising results, proper, clinically-controlled studies of the effects of CR in humans are limited.
The Comprehensive Assessment of Long-term Effects of Reducing Intake of Energy (CALERIE) is a multi-centre trial investigating whether CR can influence the ageing process in humans. The study has been conducted in two phases, the first of which was completed in 2006.
Phase 2 of CALERIE investigated the effects of CR on metabolism in over 200 subjects over the course of two years. Results of the latest study, an extension of the second phase and the most comprehensive study of its kind to date, were published Wednesday in Cell Metabolism.
53 healthy, none-obese participants (36 females and 17 males) from the CALERIE 2 study were analyzed. As part of the randomized control trial, 34 of these participants were assigned to the CR group, who restricted their calories by an average of 15% (less than their baseline) for two years. 19 participants were assigned to a control group and ate as they normally would for those two years.
After the two-year intervention, all participants were analyzed in Baton Rouge, Louisiana, at the Pennington Biomedical Research Center. A variety of tests were done in order to evaluate whether CR over the two-year period had an influence on rate of living or oxidative damage.
After two years, participants from the CR group had lost an average of 8.7 kg, while participants from the control group gained an average of 1.8 kg. After participants spent 24 hours in “state of the art” metabolic chambers, in addition to other tests of overall metabolism, it was found that those who restricted their calories had a lower metabolic rate – about 80-120 kcal/day lower than was predicted based on how much weight they lost (as metabolic rate is measured “per unit of tissue mass”).
Furthermore, it was found from testing that the production of reactive oxygen species was reduced in the CR group, meaning less oxidative damage as a result of metabolism. Together these results, according to the researchers, “[support] two long-standing theories of aging,” and indicate that CR could successfully slow the aging process and reduce age-related damage in humans.
The ground-breaking study was reported on last week in Nature.
Those who participated in the latest two-year CALERIE trial were between 21 and 50 years of age. The lead author of the study from the Pennington Center, Leanne Redman, said that “the Rolls-Royce of a human longevity study would carry on for many decades to see if people do actually live longer.”
Funding for the CALERIE trial came from the US National Institutes of Health.