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Extremely Low-Calorie Diet Won't Extend Life

Researchers Say Severely Cutting Calories Helps Rats Live Longer, but Not Humans

From the WebMD Archives

Aug. 30, 2005 -- Drastically cutting calories greatly boosts longevity for rats but probably not for people, new research shows.

It's long been known that rats live much longer than normal on extremely low-calorie diets. "You can practically double their lifespan," says researcher John Phelan, PhD, in a news release.

"The same result has been found in fish, spiders, and many other species," he continues. "If it works for them, some thought, it should work for us; I'm here to tell you it doesn't."

Phelan is an evolutionary biologist at UCLA. He and his colleagues crunched numbers from rat and human longevity studies.

Their bottom line: Severely cutting calories might extend human life a little bit, but not much, and the sacrifice likely wouldn't be worth it. The report appears in Ageing Research Reviews.

Not Your Average Diet

The researchers aren't writing about cutting out a bonbon here or there or making diets a bit leaner.

Instead, rats in longevity studies got so few calories that they could no longer reproduce. The rats simply didn't have enough energy to breed and rear the next generation.

That saved the rats a lot of effort. Without the wear and tear of parenting, their bodies got a break, and they lived longer.

But people are different. They don't give birth to litters of babies per pregnancy or reproduce as often as rats.

So even if someone starved themselves enough to shut down fertility -- and stayed that way throughout adulthood -- they wouldn't live much longer than their well-fed peers, Phelan's team reasoned.

Researcher: 'Payoffs Are Not Worth It'

"To undergo decades of calorie restriction, suffering chronically reduced fertility and increased hunger, for the sake of a much smaller proportionate increase in longevity than is seen in rodents seems unappealing and ill-advised," write the researchers.

"Our conclusion is that it is reasonably prudent assumption that calorie restriction is unlikely to be a panacea for human aging," they continue.

In a news release, Phelan also notes that rats who got few calories wore unpleasant expressions, smelled bad, and bit people who tried to hold them.

"I think about food all the time," Phelan states. "I'm not going to be 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 it because the payoffs are not worth it."

A Different View

People who restrict calories for reasons including health and longevity see things differently. They aren't necessarily out to curb calories so much that fertility fails.

The Calorie Restriction Society, a nonprofit organization promoting calorie restriction, states on its web site that calorie restriction can lead to a longer, healthier life and that it can enhance life, not make people miserable or moody.

The group also promotes losing weight very slowly, choosing nutritious foods, getting tests done to monitor health, watching out for side effects, and consulting a doctor before making any dietary changes.

Phelan and colleagues looked at calorie restriction throughout adulthood, not for shorter periods of time. In the news release, Phelan notes that the findings aren't an invitation to throw calorie caution to the winds, since obesity often brings health risks.

Show Sources

SOURCES: Phelan, J. Ageing Research Reviews, August 2005; vol 4: pp 339-350. News release, UCLA. Calorie Restriction Society web site.
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