Caloric Restriction: Friend or Foe?
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Caloric restriction is an experimental tool that utilizes "undernutrition without malnutrition." In other words, caloric restriction refers to a diet with between 30-40 percent fewer calories than is typical, but which contains all the necessary nutrients and vitamins to support life. Caloric restriction seems to slow down some of the destructive processes that take place in cells and tissues with aging. Scientists don't yet know exactly how or why it works, but have developed several theories. First of all, caloric restriction seems to reduce damage from chemical metabolic processes, particularly oxidative and glycation damage, thought to be leading causes of cell aging and death. |
On a larger scale, caloric restriction slows the effects of aging on the nervous system, the reproductive organs and the production of hormones in some animals. It has been shown to boost the immune system and delay the onset of certain age-related cancers.
Caloric restriction is the only experimental intervention, other than temperature manipulation in cold-blooded animals, studied that can conclusively increase longevity -- in experimental animals. Caloric restriction has been shown to increase both the average and the maximal life spans in paramecia, worms, spiders, insects, and rodents. Preliminary results suggest that calorie-restricted monkeys are healthier and tend to live longer than their freely fed counterparts.
Even if caloric restriction does not work in humans, studying its mechanisms is still very important. Caloric restriction seems to prevent or delay many age-associated diseases and conditions, such as heart disease, dementia, and cancer. If scientists can figure out how it works, they might be able to develop drugs that mimic its effects without requiring people to drastically reduce their calorie intake and risk potentially dangerous side effects. The main goal of mimicking caloric restriction through drugs is not necessarily to increase lifespan, but to reduce the incidence or delay the onset of age-related diseases and conditions and thereby improve the quality of later life.
UPDATE
Starving Won't Make People Live Longer
Reuters Health, By Maggie Fox
Starving -- or caloric restriction -- may make worms and mice live up to 50 percent longer but it will not help humans live super-long lives, two biologists argue.
They said that their mathematical model showed that a lifetime of low-calorie dieting would only extend human life span by about 7 percent, unlike smaller animals, whose life spans are affected more by the effects of starvation. This is because restricting calories only indirectly affects life span, said John Phelan of the University of California Lo Angeles and Michael Rose of the University of California Irvine.
Researchers at various universities and the national Institutes of Health are testing the theories but there are groups already cutting calories by up to a third in the hope they can live to be 120 or 125, while staying healthy.
"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 Phelan, an evolutionary biologist, in a statement.
The idea of caloric restriction has been gaining credence as scientists test it in more and more animals. It is easy to show that creatures that have short life spans such as mice, fish and spiders live longer if they eat less.
All things being equal, then, cutting calories by about a third should also help people to dramatically live longer and proponents of the idea are actively dieting.
"All things, however, are not equal," Phelan and Rose wrote in their report, published in the journal Aging Research Reviews. "Longevity is not a trait that exists in isolation; it evolves as part of a complex life history, with a wide range of underpinning physiological mechanisms involving, among other things, chronic disease processes."
For instance, in mice, starvation reduces fertility, which in turn lengthens life span as the animal is not stressed by repeated matings and pregnancies and the associated production of hormones, they said.
