Caloric restriction has been a hot topic in the news, with some researchers saying that humans could live to 125 by simply cutting their calorie intake. But it appears that what works in rats won't necessarily work in humans. "Our message is that suffering years of misery to remain super-skinny is not going to have a big payoff in terms of a longer life," said UCLA evolutionary biologist John Phelan. "I once heard someone say caloric restriction may not make you live forever, but it sure would seem like it." Scientists have known for some years that cutting the caloric intake of rodents by 40 percent or 50 percent results in dramatically longer lives for them. "You can practically double their life span," Phelan said. "The same result has been found in fish, spiders and many other species. If it works for them, some thought, it should work for us; I'm here to tell you it doesn't."
Phelan developed the first mathematical model demonstrating the relationship between caloric intake and longevity, using data from experiments with rodents and data from previous studies on humans, diet and longevity. Phelan and co-researcher Michael Rose have published their new findings in the journal Ageing Research Reviews.
Phelan explained how caloric restriction works. "With mice, if you restrict their caloric intake by 10 percent, they live longer than if they have unlimited access to food. 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. But the longevity gains in the mice won't be replicated in humans. "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."
The researcher's 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. Phelan explained why caloric restriction doesn't work as markedly in humans as it does in rodents. "When you restrict the caloric intake of rodents, the first thing they do is shut off their reproductive system. 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.
Phelan reckons 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 to live a few more years? You will be unhappy and then your life will end shortly after mine ends," Phelan said. "My advice about food is be sensible, and don't be a fanatic about it because the payoffs are not worth it," he concluded.
