Regular Fasting Seems To Improve Health

April 29, 2003

WASHINGTON (AP) -- The health benefits of sharply cutting calories may occur after periodic fasting, even if the fast does not result in eating less overall, a new report indicates.

Scientists are now planning a study to see if fasting, which seems to benefit mice, will also be good for people too.

Benefits ranging from longer life to less stress and greater sensitivity to insulin have been reported in recent studies of severe reductions in diet.

But mice that were fed only every other day, but were allowed to gorge themselves on the days they ate, had similar health benefits to ones on a diet reduced by 40 percent of normal food intake, a team of researchers reports in Tuesday's online edition of Proceedings of the National Academy of Sciences.

While the cause of health improvements from cutting back on diet isn't fully understood, many researchers had assumed that a long-term reduction in calories was involved.

The new study by Mark Mattson and colleagues at the National Institute on Aging found equal benefits, however, for mice that ate only every other day, even if they didn't cut total calories, because they ate twice as much on days they weren't fasting.

Mattson said a study is being planned to test the effect of fasting on people. The plan is to compare the health of a group of people fed the normal three meals a day with a similar group, eating the same diet and amount of food, but consuming it within four hours and then fasting for 20 hours before eating again.

"Overeating is a big problem now in this country. It's particularly troublesome that a lot of children are overweight. It's still unclear the best way to somehow get people to eat less," Mattson said.

"One possibility is skipping a meal a day. Our study suggests that skipping meals is not bad for you."

Dr. Carol Braunschweig of the University of Illinois at Chicago, who was not part of the study team, said she was intrigued by the suggestion that a drastic change in eating patterns might have benefits.

"With the current epidemic of obesity and physical inactivity facing the U.S. today, identification of a beneficial eating pattern that could address some of the untoward effects of excess weight would be a very significant finding," she said.

Mattson said an earlier study found that mice that fasted every other day had extended life spans. The new experiment found the mice also did better in factors involved in diabetes and nerve damage in the brain similar to Alzheimer's disease, he said.

"We think what happens is going without food imposes a mild stress on cells, and cells respond by increasing their ability to cope with more severe stress," Mattson said. "It's sort of analogous to physical effects of exercise on muscle cells."

He said the researchers think this stress occurs throughout the body, which might be the reason fasting seems to increase life span and the animals become more resistant to the diseases of aging.

The dieting mice consumed 40 percent less food than mice eating normally and lost nearly half their body weight (49 percent) in the experiment, while the fasting mice weighed only a little less than mice eating normally.

In recent years, some nutritionists have recommended eating smaller amounts more often, but this study did not deal with that type of eating pattern.

In the new report, the researchers said both the fasting mice and those on a restricted diet had concentrations of blood sugar and insulin that were significantly lower than mice allowed to eat whenever they wanted. Indeed, insulin levels in the fasting mice were even a bit lower than the dieting ones.

At the end of the experiment all three groups of mice were injected with a toxin that damages cells in the part of the brain called the hippocampus. Cell damage there is involved in Alzheimer's in humans.

When the mouse brains were later analyzed the scientists found that the brains of the fasting mice were more resistant to damage by the toxin than the brains of either dieting mice or those eating normally.