There has been a belief that has been promoted over the years that very low calorie diets can promote lifespan. It was based on a 1934 research study from Mary Crowell and Clive McCay, at Cornell University, who observed that laboratory rats fed a severely reduced calorie diet, while maintaining micronutrient levels, would result in lifespans of up to twice as long as control groups. Their findings were later repeated by Roy Walford, and his student Richard Weindruch, through a series of experiments with mice. In 1986, Weindruch reported that restricting the caloric intake of laboratory mice proportionally increased their life span compared to a group of mice with a normal diet. The calorie-restricted mice also maintained youthful appearances and activity levels longer and showed delays in age-related diseases. The results of the many experiments by Walford and Weindruch were summarized in their book, The Retardation of Aging and Disease by Dietary Restriction.
These findings have since been repeated in other animals and have been accepted by other researchers. Also, there have been investigations into possible physiological similarities between humans and other animals to determine if a calorie restricted diet may have an impact on human lifespan or aging. Of course, there are many anecdotal stories of individuals adopting the practice of calorie restrictions, but no randomized clinical trials have been undertaken to determine if this type of diet has any effect at all.
If one is going to look at models for human diets and lifespan, then primates, being our closest living relatives, would be a good proxy for experimentation until a long-term (and when discussing long-term, it might be a 20-years or longer) study is published. The National Institute on Aging sponsored a long-term study using rhesus macaques, known commonly as rhesus monkeys, to determine whether calorie restricted diets had any effect on aging. The results of the study were recently published in Nature. The article, Impact of caloric restriction on health and survival in rhesus monkeys from the NIA study, concluded that genetics and healthy diets probably matter more than calorie restrictions in extending lifespans. Over a 23-year study period, the monkeys that were fed a severely low-calorie diet didn’t live any longer than the normal-diet control group, contradicting research in some other animals that had suggested otherwise. The thinner monkeys did seem healthier by some measures, but the calorie restriction failed to alter either cause of death or survival according to the research data.
The authors of the study also discussed why their results might have varied from results in other studies with other animal models–they seem to have included better food quality for both calorie restricted and unrestricted groups, and better control over genetic variability of their animals. In other studies with rhesus macaques, the control group was actually fed an unhealthier food source with higher sucrose and lower essential oils than the ones used in the newer studies, which made the older studies’ control monkeys appear unhealthier. With better control over food sources and genetic variability of the animals, we might be able to examine different research directions about what factors are causal to aging.
According to the Nature News report on the study,
- Control of aging is not going to be simple. Don’t expect that we’re going to find a single on/off switch. According to the report, “…hopes that ageing could be delayed by targeting a single gene or protein in a single molecular pathway have faded, as researchers have learned that the key pathways vary according to the animal.“
- There is just no evidence that caloric restriction has any effect on humans. And now, in a well designed study using a primate proxy, we still have no evidence that a restricted calorie diet can lengthen lifespan. Some studies have concluded that people of average weight tend to live the longest. On the other hand, Nir Barzilai, a gerontologist at Albert Einstein College of Medicine in New York, says that the centenarians he studies have led him to believe that genetics is more important than diet and lifestyle. He is quoted in the Nature News article stating that, “They’re a chubby bunch.”
So once again. Genes probably more than anything, and you can’t control that, at least for now. And we still haven’t got a useful recommendation about what makes a good diet.