The science of calorie restriction just got a lot more complicated.
Rhesus monkeys fed experimental low-calorie diets didnt live any longer than their high-calorie brethren, a result that conflicts with a 2009 report of long-lived, extra-low-calorie monkeys.
That had been the first demonstration of extended lifespans in primates, not just lab rodents, and raised hopes of the diet being a dinner-plate fountain of youth. The new findings seem to challenge that notion, though theyre far from conclusive.
More fundamentally, the findings pop the lid on a roiling scientific back-and-forth over calorie restrictions effects and mechanisms, a matter of vigorous contention thats belied by popular notions of the diet as a simple, straightforward longevity hack.
From the beginning, there have been people who were true believers in the effects of calorie restriction in every single species, said Rafa de Cabo, a National Institute on Aging gerontologist and co-author of the new study, published Aug. 29 in Nature. Often attention wasnt paid to data showing that in some cases calorie restriction wasnt good, or didnt produce the effects it should have.
De Cabos experiment started in 1987, right around the time as another, similar experiment at the University of Wisconsin. Both groups wanted to know whether calorie restriction cutting intake by up to 40 percent below whats typically considered healthy would have the same health-protecting, life-prolonging effects in primates that it seemed to have in lab animals.
In 2009, the Wisconsin group reported that CR, as the diet is known, indeed extended their monkeys lifespans. But in the new study, researchers led by de Cabo and fellow NIA gerontologist Julie Mattison report no extension, at least in monkeys who started CR in middle age or late in their lives. (Monkeys who started during infancy arent yet old, so their longevity results wont be known for another decade or so.)
De Cabo and Mattisons CR monkeys, 57 in total, have shown signs of better health, though theyre mixed. For example, males have low cholesterol and blood sugar, but not females. And even across-the-board health improvements would be underwhelming in comparison to calorie restrictions sometimes overwhelming expectations.
What some people were hoping is that CR would extend longevity beyond the normal, that with a good CR diet you would live for 120 years, said gerontologist Steven Austad of the University of Texas, who was not involved in the study. I think these studies show together that diet is not, no matter how you do it, going to get people living to 120.
Austads own work found that CR didnt work on descendants of mice recently caught in the wild, rather than bred from lab-adapted mice that may be so unnatural and intrinsically unhealthy as to give misleading results.
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Experimental Low-Calorie Diet Gets Puzzling Results in Monkeys
