WASHINGTON -- Starving -- officially known as 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 argued on Sunday.

They said 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.

COMPUTER MODEL OF LIFE SPAN

They came up with a mathematical model based on the known effects of calorie intake and life span.

"In Japanese populations, for example, the normal male diet is approximately 2,300 kilocalories (calories) per day," they wrote -- and the average life span for a Japanese male is 76.7 years.

"Sumo wrestlers, however, consume an average of approximately 5,500 calories per day and have a life expectancy of 56 years," they added.

People living on the Japanese island of Okinawa eat somewhat less than the average Japanese. They also live slightly longer. This could give a basis for calculating the benefits of eating less.

Calculations based on the Okinawa and sumo wrestler data suggest that if Japanese people ate just 1,500 calories a day, the longest average life span attainable would be just under 82 years, Phelan and Rose wrote.

Researchers are trying to find out if perhaps some genetic elements of eating less may explain the effects on mice -- and someday might be translated into people.

In the current issue of the journal Science, Hiroshi Kurosu of the University of Texas Southwestern in Dallas and colleagues found that mutant mice who produced too much of a gene called Klotho lived longer.

It affected a process called the insulin-like growth factor-1 signaling pathway, they reported.

"Klotho protein may function as an anti-aging hormone in mammals," Kurosu and colleagues wrote.

Source: REUTERS/By Maggie Fox, Health and Science Correspondent