Rhesus monkeys on calorie-restricted diets age just as quickly as their chubbier counterparts.

E. Bmsch/Imagebroker/FLPA

To those who enjoy the pleasures of the dining table, the news may come as a relief: drastically cutting back on calories does not seem to lengthen lifespan in primates.

The verdict, from a 25-year study in rhesus monkeys fed 30% less than control animals, represents another setback for the notion that a simple, diet-triggered switch can slow ageing. Instead, the findings, published this week in Nature1, suggest that genetics and dietary composition matter more for longevity than a simple calorie count.

To think that a simple decrease in calories caused such a widespread change, that was remarkable, says Don Ingram, a gerontologist at Louisiana State University in Baton Rouge, who designed the study almost three decades ago while at the National Institute on Aging (NIA) in Bethesda, Maryland.

When the NIA-funded monkey study began, however, studies of caloric restriction in short-lived animals were hinting at a connection. Experiments had showed that starvation made roundworms live longer. Other studies had showed that rats fed fewer calories than their slow and balding brethren maintained their shiny coats and a youthful vigour. And more recently, molecular studies had suggested that caloric restriction or compounds that mimicked it might trigger a cascade of changes in gene expression that had the net effect of slowing ageing.

In 2009, another study2, which began in 1989 at the Wisconsin National Primate Research Center (WNPRC) in Madison, concluded that caloric restriction did extend life in rhesus monkeys. The investigators found that 13% of the dieting group died from age-related causes, compared with 37% of the control group.

One reason for that difference could be that the WNPRC monkeys were fed an unhealthy diet, which made the calorie-restricted monkeys seem healthier by comparison simply because they ate less of it. The WNPRC monkeys diets contained 28.5% sucrose, compared with 3.9% sucrose at the NIA. Meanwhile, the NIA meals included fish oil and antioxidants, whereas the WNPRC meals did not. Rick Weindruch, a gerontologist at the WNPRC who led the study, admits: Overall, our diet was probably not as healthy.

Further, the WNPRC control group probably ate more overall, because their meals were unlimited, whereas NIA monkeys were fed fixed amounts. As adults, control monkeys in the WNPRC study weighed more than their NIA counterparts. Overall, the WNPRC results might have reflected an unhealthy control group rather than a long-lived treatment group. When we began these studies, the dogma was that a calorie is a calorie, Ingram says. I think its clear that the types of calories the monkeys ate made a profound difference.

When we began these studies, the dogma was that a calorie is a calorie.

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Calorie restriction falters in the long run

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