Calorie restriction improves health and extends life in nearly all shorter-lived species examined to date. In mice life span can be extended by 40% or more this way, but theorists don't expect an outcome of the same magnitude to take place in human calorie restriction practitioners. Firstly, our ancestors would certainly have noticed such a large effect at some point in the past few thousand years, and at the very least in the past few hundred. Secondly, longevity resulting from calorie restriction is thought to have evolved to enable greater resistance to seasonal shortages of food. A season is a short time for a human, but a long time for a mouse - and thus only the mouse has the evolutionary pressure to develop a very plastic life span in response to food availability.
Nonetheless, the calorie restriction response evolved very early on in the tree of life, and the short term effects in mice and humans are surprisingly similar. In human studies from recent years the practice of calorie restriction is shown to produce very favorable changes to metabolism and health, far greater and better than can be achieved with any present drug or medical technology. It's the same situation as exists for exercise: if either were a drug it would outsell every pharmaceutical created to date. But trying telling people they should exercise more and eat less and see how far you get.
Short-term studies are one thing, but studying calorie restriction over the long term in long-lived species is a big investment. A pair of primate studies that record the effects of calorie restriction on health and life span started decades ago and are still underway. One runs under the auspices of the NIA, the other at the University of Wisconsin-Madison. You may recall that the NIA researchers published results back in 2012 that suggested calorie restriction does not in fact have any significant effect on primate longevity. Some of the research community have in turn pointed out that the NIA study has potential issues, but I won't rehash all of that here as it is covered in the article quoted below. You might look back at these posts for background:
- Considering a Negative Result for Primate Calorie Restriction
- No Extension of Average Lifespan in Primate Study of Calorie Restriction
The latest results from the Wisconsin-Madison study have now been published, and they are more positive and more in line with what we'd expect based on short term response to calorie restriction in primates, humans included.
The latest results from a 25-year study of diet and aging in monkeys shows a significant reduction in mortality and in age-associated diseases among those with calorie-restricted diets. The study of 76 rhesus monkeys was performed at the Wisconsin National Primate Research Center in Madison. When they were 7 to 14 years of age, the monkeys began eating a diet reduced in calories by 30 percent. The comparison monkeys, which ate as much as they wanted, had an increased risk of disease 2.9 times that of the calorie-restricted group, and a threefold increased risk of death.
Still, the effects of caloric restriction on primates have been debated. An influential 2012 report on 120 monkeys being studied at the National Institute of Aging (NIA) reported no differences in survival for caloric restriction animals and a trend toward improved health that did not reach statistical significance.
The discrepancy may be a result of how the feeding was implemented in control animals in the NIA study. "In Wisconsin, we started with adults. We knew how much food they wanted to eat, and we based our experimental diet on a 30 percent reduction in calories from that point." In contrast, the NIA monkeys were fed according to a standardized food intake chart designed by the National Academy of Science. The Wisconsin researchers concluded that the NIA controls were actually on caloric restriction as well. "At all the time points that have been published by NIA, their control monkeys weigh less than ours, and in most cases, significantly so."
Twenty monkeys entered the NIA study as mature adults, 10 in the test group and 10 in the control group, and five of these (four test monkeys and one control monkey) lived at least 40 years. "Heretofore, there was never a monkey that we are aware of that was reported to live beyond 40 years. Hence, the conclusion that caloric restriction is ineffective in their study does not make sense to me and my colleagues."
This should all be filed away under basic good health practices. Yet calorie restriction, including attempts to recreate its effects on metabolism through drugs and targeted manipulation of gene expression, is the not the path to greatly extended longevity. It is among the best of presently available paths to raising your odds of having a better old age, which is good in and of itself, but you can't calorie restrict yourself to a decent chance of living to see 100. A good 99% of the people with the best diets and lifestyles die without seeing a century of life. The only thing that will make a significant difference to your prospects of great and healthy longevity is faster progress towards rejuvenation treatments - ways to prevent and reverse the course of aging. They don't exist yet, but they could in the decades ahead. Here and now that means fundraising and advocacy: pushing SENS and similar repair-based approaches to treating aging into the research mainstream.