Many studies in animals have shown that animals on a calorie-restricted diet have longer life spans. But there is limited evidence of the same effect in humans. Even if a restricted-calorie diet should turn out not to prolong life, there are indications that it can improve other conditions, such as insulin resistance, cardiovascular health and obesity.
Calorie Restriction
A calorie-restricted diet restricts calories by 20 to 40 percent, relative to an average calorie intake, but it optimizes the intake of essential nutrients. The diet cuts processed carbohydrates and sugar and adds a variety of whole foods, especially fruit and vegetables but also food vegetable oils, lean meat and fish. At first, a calorie-restricted diet leads to weight loss but, over time, the body adapts to the new caloric environment and lowers its rate of metabolism.
First Indication in Humans
A study published in the September 2004 issue of "Journal of Gerontology: Biological Sciences" indicates that a calorie-restricted diet prolongs life in humans. The study looked at the lifespans of 1,915 non-smoking Japanese men who participated in a heart study 36 years earlier. The data showed a trend between a calorie-restricted diet and a long lifespan. Those who naturally restricted calories to about 1,900 kilocalories a day had the longest lifespans. This is 600 kcals below the average calorie intake in American men. The main limitation of the study is that it didn't look at possible changes in the participants' diet during the 36 years between the initial dietary observations and the analysis of lifespan.
Mechanism of Action
Despite the amount of evidence that animals on calorie-restricted diets have prolonged lifespans, it's not really known how or why the diet works in the animals. A review article published in the January 2003 issue of "Gene Development" looks at a number of possible mechanisms of action of calorie-restricted diets. The most promising explanation of the promotion of longevity, the authors say, is that restricting calories induces changes in the neuroendocrine system, the system that receives input from the brain and releases hormones into the bloodstream as a result. They emphasize that the promotion of longevity in humans is multidimensional. The lower intake of calories affects the secretion of numerous hormones, including insulin and growth hormone. Restricting the secretion of these hormones help prevent cell damage.
Length of Your Life
How long can you reasonably expect to live on a calorie restricted diet? A mathematical model published in the August 2005 issue of "Ageing Research Review" and based on animal and human studies of longevity suggests that you live about 3 to 7 percent longer on a calorie-restricted diet. If you would reach 100 on a normal diet, you might be around until you are between 103 and 107 on a calorie-restricted diet. The 3 to 7 percent increase in longevity in humans is much less than the 20 percent increase seen in rodents.
References
- Fight Aging: Calorie Restriction Explained
- "Journal of Gerontology: Biological Sciences"; How Much Should We Eat? The Association Between Energy Intake and Mortality in a 36-Year Follow-Up Study of Japanese-American Men; Bradley J. Willcox, et al.; September 2004
- "Genes Development"; How Does Calorie Restriction Work?; Jana Koubova and Leonard Guarente; January 2003
- "Ageing Research Reviews"; Why Dietary Restriction Substantially Increases Longevity in Animal Models but Won't in Humans; John Phelan and Michael Rose; August 2005
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