Severely restricting calories over decades may add a few years to ahuman life span, but will not enable humans to live to 125 and beyond,as many have speculated, evolutionary biologists report.
"Our message is that suffering years of misery to remainsuper-skinny is not going to have a big payoff in terms of a longerlife," said UCLA evolutionary biologist John Phelan. "I once heardsomeone say caloric restriction may not make you live forever, but itsure would seem like it. Try to maintain a healthy body weight, butdon't deprive yourself of all pleasure. Moderation appears to be a moresensible solution.
"With mice, if you restrict their caloric intake by 10 percent,they live longer than if they have unlimited access to food," Phelansaid. "If you restrict their intake by 20 percent, they live evenlonger, and restrict them to 50 percent, they live longer still; butrestrict their intake by 60 percent and they starve to death.
"Humans, in contrast, will not have rodent-like results fromdramatically restricting calories," he said. "Caloric restriction isnot a panacea. While caloric restriction is likely to be almostuniversal in its beneficial effects on longevity, the benefit to humansis going to be small, even if humans restrict their caloric intakesubstantially and over long periods of time."
Phelan developed the first mathematical model demonstrating therelationship between caloric intake and longevity, using representativedata from controlled experiments with rodents, as well as publishedstudies on humans, diet and longevity. He and Michael Rose, professorof ecology and evolutionary biology at the University of California,Irvine, published their findings in a journal article titled, "Whydietary restriction substantially increases longevity in animal modelsbut won't in humans," published in the August issue of thepeer-reviewed journal Ageing Research Reviews.
Their mathematical model shows that people who consume the mostcalories have a shorter life span, and that if people severely restricttheir calories over their lifetimes, their life span increases bybetween 3 percent and 7 percent -- far less than the 20-plus years somehave hoped could be achieved by drastic caloric restriction. Heconsiders the 3 percent figure more likely than the 7 percent.
"The trade-off between calories and longevity appears to beclose to a linear relationship, but the slope isn't very steep," saidPhelan, whose model predicts the relationship between calories consumedand life span.
Phelan's conclusion is that the few extra years of life are not worth the suffering necessary to achieve them.
"Do you want to spend decades severely limiting what you eat tolive a few more years? You will be unhappy and then your life will endshortly after mine ends," Phelan jokes.
Scientists have known for six decades that cutting the caloricintake of rodents by 40 percent or 50 percent results in dramaticallylonger lives for them.
"You can practically double their life span," Phelan said. "Thesame result has been found in fish, spiders and many other species. Ifit works for them, some thought, it should work for us; I'm here totell you it doesn't."
Phelan, co-author of the book, "Mean Genes," conducted hisdissertation at Harvard University 10 years ago on caloric restrictionand on why it works in extending the lives of rodents.
"When you restrict the caloric intake of rodents, the firstthing they do is shut off their reproductive system," said Phelan,citing a finding from his dissertation. A normal rodent reachesmaturity at one month of age, and begins reproducing its body weight inoffspring every month and a half. If humans shut off reproduction byseverely limiting calories, "our reduction in wear and tear on the bodyis minimal," he said.
The rodents placed on severely restricted diets bit people whotried to hold them, and had an unpleasant demeanor, unlike the moredocile animals given more "normal" amounts of food, Phelan said.
"I think about food all the time," he said. "I'm not going tobe so extreme that I become the mouse that bites anyone who touches me.My advice about food is be sensible, and don't be a fanatic about itbecause the payoffs are not worth it."
While the relationship between how much you eat and your lifespan is not so dramatic, there are very real costs of being overweight-- including greater risk for heart disease and other life threateningillnesses, Phelan said.
The human data factored into the mathematical model include thecaloric intake of people in Japan, and their longevity, compared withsumo wrestlers, who consume more than twice the normal male diet, andmen in Okinawa, Japan, who consume less than the average Japanese male.
Ageing Research Reviews is a quarterly journal respected in the field of gerontology.
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