According to a 25-year study using rhesus monkeys, a lifetime on a very-low calorie diet did not help them live any longer, researchers from Louisiana State University in Baton Rouge reported in the journal Nature. Rhesus monkeys are genetically relatively similar to humans. They were fed on a diet consisting of 30% fewer calories than the control group were for a quarter of a century.
The authors say that there are two factors which have the largest impact on lifespan:
- Good genes
- A healthy and well balanced diet
Don Ingram, a gerontologist who designed the study nearly thirty years ago while he was at the NIA (National Institute on Aging), said “To think that a simple decrease in calories caused such a widespread change, that was remarkable.”
At the start of the study, there were already suggestions that severe calorie restriction over the long term might have a positive impact on longevity. Several studies had shown that half-starving roundworms lived much longer than their well-fed counterparts. Animal studies with rats had demonstrated how low-calorie diets kept them youthful for longer.
Scientists from the Washington University School of Medicine, in St. Louis, Missouri, proposed that low-calorie diets reduce a human’s core body temperature, resulting in longer life.
A study carried out by researchers from the Department of Genetics Evolution and Environment at University College London, published an article in Nature which said that high protein diets make us live longer, not low calorie ones.
A recent study indicated that restricting calories may trigger a genetic domino-effect resulting in slower aging.
A 2009 study carried out at the Wisconsin National Primate Research Center (WNPRC) found that 13% of rhesus monkeys on very low calorie diets died from age-related causes, compared to 37% in the “normal-diet” group.
Ingram believes that the WNPRC experiment had a flaw – the diets in both groups were unhealthy. An unhealthy low calorie diet is less bad for you than an unhealthy higher calorie one. Their diets contained 28.5% sucrose, compared to this recent one where sucrose made up only 3.9% of their total dietary calories. The NIA monkeys also consumed fish oil and antioxidants, the WNPRC ones did not.
The WNPRC study leader, Rich Weindruch, said himself that his monkeys’ diet was probably less healthy.
Also, portions were not controlled in the WNPRC experiment, the animals had unlimited access to their food, while the NIA monkeys did not, they received fixed amounts each day. Consequently, the WNPRC monkeys in both groups weighed more than those in the equivalent groups in the NIA study. Ingram believes the WNPRC study demonstrated the difference between an unhealthy control group and another group on another diet, rather than a healthy control group versus a low-calorie one.
“When we began these studies, the dogma was that a calorie is a calorie. I think it’s clear that the types of calories the monkeys ate made a profound difference.”
The authors suggest that mixed results from various animal experiments probably reflect genetic diversity among strains. The NIA monkeys came from a gene pool from India, while the WNPRC ones came from other genetic lines from China and India.
Scientists had expected to be able to shut down one gene, open up another, and in this way find pathways for restricting disease and slowing down the aging process. However, they say that key pathways are not all the same, they vary from animal to animal.
David Sinclair, a geneticist at Harvard Medical School in Boston, Massachusetts, said “It may take us a decade to sort out longevity networks.”
Surprisingly, evidence on caloric restriction linked to slower aging in human beings is scarce, the authors say. According to observational studies, humans who live the longest are of average weight – not thin people on low calorie diets.
According to Nir Barzilai, a gerontologist at Albert Einstein College of Medicine, New York, centenarians have talked to him and given him the impression that genetics has a much greater impact on longevity than lifestyle or diet. He described centenarians as “a chubby bunch”.
Ingram, who says he enjoys good food, says he welcomes studies that focus on diet composition rather than mathematics (pure caloric intake).
“Is the human lifespan fixed? I still don’t believe that for a minute.”
Scientists at the Washington University School of Medicine in St. Louis in 2008, had already put forward the suggestion that low-calorie diets may make rodents live longer, but they might not be as effective in humans.
Written by Christian Nordqvist