An odd-sounding approach to living longer gets a boost when two teams of researchers compare notes.
By Nathan Collins
(Photo: Spencer Platt/Getty Images)
It might sound at first like a downright kooky idea: If you want to live longer, eat less. More specifically, eat a lot less—like 25 percent fewer calories than the usual recommendations. The evidence in support of that idea, called caloric restriction, had been mixed, but now two teams previously on opposite sides of the debate report the approach really does work … sometimes ... in monkeys.
The idea of caloric restriction (CR) goes back to at least the 1930s, when researchers first noticed that lab rats lived as much as 40 percent longer when fed 30 percent fewer calories. But does that work for other species? In particular, could it work for rhesus monkeys, one of our closest relatives in the animal kingdom?
In the 1980s, two separate teams—one at the National Institute on Aging and another at the University of Wisconsin—launched independent, decades-long projects to find out. The NIA study, which fed a total of 121 monkeys of varying ages either a normal diet or a restricted one, concluded caloric restriction had no effect on how long the monkeys survived. The University of Wisconsin study did the same thing with 76 adult rhesus monkeys, and those researchers discovered just the opposite: After 20 years, four in five of the restricted-diet monkeys were still alive, compared to just half of the ordinary-diet monkeys.
Rather than bicker about who was right, the two teams, now led by Rozalyn Anderson and Rafael de Cabo, got together to try to figure out why they got such different results. The answer, unsurprisingly: They did their experiments a little bit differently, in a number of different ways. For one thing, the NIA study put monkeys on calorie-restricted diets starting at different ages, while the UW study put all of their moneys on those diets at around age eight, when they’d reached their full size. The monkeys themselves were also different—the UW monkeys were all of Indian extraction, while the NIA monkeys were a mix of Indian and Chinese. Meals differed as well in terms of size, number, timing, and nutritional content.
“Data from both study locations suggest that the CR paradigm is effective in delaying the effects of aging in nonhuman primates but that the age of onset is an important factor in determining the extent to which beneficial effects of CR might be induced,” the joint team writes in Nature Communications. In particular, the UW monkeys on restricted diets weighed less, had less body fat, and had a lower risk of death than control monkeys.
But if that’s true, what’s the deal with the adult and older NIA monkeys, for whom CR diets appeared to have no effect? As it turns out, all of the NIA monkeys were eating less than the UW restricted-diet monkeys. As a result, the NIA monkeys weighed less and lived longer than any of the UW monkeys, including UW’s CR monkeys. One of NIA monkeys, in fact, is currently a record-setting 43 years old, the team reports.
Data on the NIA’s younger monkeys was more complicated, with CR diets having much more of a positive impact on male rather than female monkeys.
There is, therefore, much more to figure out about whether CR diets have a positive effect on health—not to mention why—but at least researchers now know that basic idea works. “Given the obvious parallels between human and rhesus monkey, it seems highly likely that the beneficial effects of CR would also be observed in humans” as well, the team concludes.