According to study by University of California - Los Angeles ( UCLA ) researchers, severely restricting calories over decades may add a few years to a human life span, but will not enable humans to live to 125 and beyond.

" With mice, if you restrict their caloric intake by 10 percent, they live longer than if they have unlimited access to food," John Phelan said. " If you restrict their intake by 20 percent, they live even longer, and restrict them to 50 percent, they live longer still; but restrict their intake by 60 percent and they starve to death.

" Humans, in contrast, will not have rodent-like results from dramatically restricting calories," he said. " Caloric restriction is not a panacea. While caloric restriction is likely to be almost universal in its beneficial effects on longevity, the benefit to humans is going to be small, even if humans restrict their caloric intake substantially and over long periods of time."

Phelan developed the first mathematical model demonstrating the relationship between caloric intake and longevity, using representative data from controlled experiments with rodents, as well as published studies on humans, diet and longevity. He and Michael Rose, at the University of California, Irvine, published their findings in an article titled, " Why dietary restriction substantially increases longevity in animal models but won't in humans," in the journal Ageing Research Reviews.

Their mathematical model shows that people who consume the most calories have a shorter life span, and that if people severely restrict their calories over their lifetimes, their life span increases by between 3 percent and 7 percent -- far less than the 20-plus years some have hoped could be achieved by drastic caloric restriction. He considers the 3 percent figure more likely than the 7 percent.

" The trade-off between calories and longevity appears to be close to a linear relationship, but the slope isn't very steep," said Phelan, whose model predicts the relationship between calories consumed and life span.

Phelan's conclusion is that the few extra years of life are not worth the suffering necessary to achieve them.

Scientists have known for six decades that cutting the caloric intake of rodents by 40 percent or 50 percent results in dramatically longer lives for them.

" When you restrict the caloric intake of rodents, the first thing they do is shut off their reproductive system," said Phelan. A normal rodent reaches maturity at one month of age, and begins reproducing its body weight in offspring every month and a half. If humans shut off reproduction by severely limiting calories, "our reduction in wear and tear on the body is minimal," he said.

Source: University of California - Los Angeles, 2005


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