It's an approach based on science showing that limiting proteins and sugars seems to impede processes in the body that lead to diabetes and even cancers. But it's also a tough road that can sap dieters' patience and strength, said University of Southern California ageing researcher Valter Longo, who recently led a study searching for a better way to get the benefits of fasting without so much pain.

"We wanted to know, what if you let people eat normally, but then once every few weeks you fool the system into thinking it was starving?" he said.

The results of Longo's experiment, published last week in the journal Cell Metabolism, showed that the fasting-mimicking plan did work.

The research was conducted in three parts: in yeast, in mice and in people.

When Longo's team alternated between offering yeast a nutrient medium and fasting them, they lived longer. Middle-aged mice that were fed a diet that mimicked fasting lived longer and had less fat, fewer cancers, less bone density loss and other positive effects.

To begin to understand the effects of a fasting-like diet on people, the team organised aclinical trial involving 38 healthy subjects aged 18 to 70. Half the group were randomly put in a control group that ate normally, returning for testing at the end of the three-month study.

The other half went through three five-day-long monthly cycles of the fasting-mimicking diet. Their food, which was all plant-based, with low carbohydrates, low protein and high levels of healthy fat, was delivered to them in a box and included powdered soups, nut bars and chips. It provided about 1090 calories on the first day and about 725 calories on days two through to five.

"We try to make it as close as possible to something that looks like normal food," Longo said, adding that 95 per cent of the dieters stuck with the plan - a success rate that surprised the researchers.

"I think people noticed a lot of results, and that motivated them to come back," he said.

The test subjects who ate the special diet experienced drops in their fasting blood glucose levels and in factors associated with cancer and cardiovascular risk. In mice, the researchers saw increased numbers of stem cells, suggesting that starvation-like conditions killed off old, weaker cells and allowed younger, refreshed cells to emerge.

"Everything is getting a little younger and it goes back to working much better," Longo said.

He and his colleagues are almost finished with another study with 70 to 80 subjects and soon will meet Food and Drug Administration officials to see whether the diet might be appropriate for people with illnesses such as cancer - to reduce recurrences, for example, by prescribing a fasting-mimicking food plan.

Some day, he said, doctors might want to begin prescribing similar diets for patients with markers showing they are at risk for cancers and other illnesses - much as physicians today prescribe special diets and medications for patients with high cholesterol who are at risk for heart disease. (Longo has equity in the USC-backed medical food company L-Nutra; data analysis for the Cell Metabolism study was conducted by scientists who had no ties to the venture, he said.)

Longo, who eats sparingly and healthily, says he follows the stricter regimen once or twice a year and emphasised that people should not experiment with such diets without medical supervision.

LOS ANGELES TIMES