American Association: Ageing - The diet that can put years on your life

How to live longer, be happier and avoid Marilyn Monroe syndrome

A SCIENTIST who spent two years locked away in a giant experimental glasshouse in the Arizona desert said he has found evidence to support the theory that a carefully restricted diet might extend human life.

Roy Walford, professor of pathology at the University of California at Los Angeles and a pioneer of "caloric restriction" - the idea that a strict diet can counter the effects of ageing - said he has the first data to suggest it might work in humans.

Professor Walford was one of the eight men and women who took part in the Biosphere 2 experiment between 1991 and 1993, living in a sealed environment as a test for future colonisation of the Moon or Mars. During the two years they ate a controlled diet rich in nutrients but low on high-calorie food

An analysis of blood samples taken during the experiment has found the same changes in certain biological markers seen when lab animals are forced to undergo a calorie-restricted diet.

Experiments on mice and rats demonstrate that a severely restricted diet, when calorie intake is reduced by up to half, results in a significantly extended lifespan. The longevity of one strain of mouse went from 38 to 56 months - equivalent in human terms to living 120 years.

"The Biosphere 2 study suggests that severe calorie restriction does not undermine health, as long as people receive adequate nutrition. Rather, a low-calorie diet may significantly enhance health by reducing certain risk factors, such as high blood pressure and cholesterol," Professor Walford said.

"Biosphere 2 proved that people on a restricted calorie intake can perform well physically and intellectually, even for two years in a challenging environment."

Professor Walford, who was the medical physician on the project, told the American Association for the Advancement of Science meeting in Los Angeles that experiments on monkeys have produced similar results. "The diet inside Biosphere 2 was essentially vegetarian. The animal facility provided small quantities of goats' milk, goat meat, pork, chicken, fish and eggs."

Over the course of their stay, the four men lost an average of 18 per cent of their body weight, and the women 10 per cent.

Some scientists, such as Professor Tom Kirkwood, an ageing expert at Manchester University, have criticised the theory of calorie restriction, because laboratory animals are usually allowed free access to food and thus are usually grossly overweight and in poor health, which means they die earlier than they should.

However, Professor Walford said the criticism was unjust because with each decrease in calorie intake there is a corresponding increase in the life-span of the animals.

Rats on a calorie-restricted diet are generally more active but they are not as interested in sex, although they remain fertile longer. "They are not as sexy but they are sexy for longer," Professor Walford said.