Cutting calories by fasting every other day may make cells less prone to becoming cancerous, the results of a study in mice suggest.

Scientists at the University of California, Berkeley, found that when they put mice on a routine of alternate-day fasting, it reduced the rate at which the animals’ body cells divided and proliferated. Because cancer begins when abnormal cells are allowed to divide and spread unchecked, this slowed-down cell division could theoretically reduce the risk of tumor development.

However, it’s too soon to draw that conclusion, since the study did not look at cancer incidence among the animals, said Dr. Marc Hellerstein, who led the research.

But, he told Reuters Health, “I think everyone would agree that if you reduce cell proliferation in cancer-prone tissue you’ve done a good thing.”

The study, to be published in the May issue of the American Journal of Physiology, Endocrinology and Metabolism, adds to a growing body of evidence that links calorie cutting to both longer life and lower cancer risk in animals.

Whether fasting could help people lower their cancer risk or prolong their lives is not yet known. But the encouraging finding from this study, the authors say, is that it didn’t take substantial calorie deprivation to spur the potentially beneficial cellular changes.

The mice fasted four days a week and allowed to eat as much as they wanted on non-fasting days. The net effect was a five-percent lower-than-normal calorie intake, which in humans would amount to eliminating about 100 calories per day.

The impact of this modest calorie reduction on cell division was nearly as significant as what Hellerstein’s team saw in a group of mice whose calorie intake was slashed by one third.

Much research interest of late has gone toward the possible benefits of calorie restriction, in which calories are limited but not to the point of malnutrition. Calorie reduction has been shown to extend the lifespan, with studies demonstrating the phenomenon in species ranging from yeast to fish to some mammals.

There are a number of theories on why limiting food might make for a longer, healthier life. One idea is that slowing the rate of metabolism reduces the generation of oxygen free radicals, potentially cell-damaging molecules that are a normal byproduct of the metabolic process.

When it comes to cancer specifically, research has suggested that calorie cutting could be beneficial in a number of ways - with reduced cell proliferation being one.

Exactly why fasting or general calorie restriction might dampen cell proliferation is unclear, according to Hellerstein, but he said it is likely to be related to metabolic effects.

“I think that a tremendous signal kicks in” when the body is deprived of food, Hellerstein said. What the signal or signals are is unknown, but one possible player, according to the researcher, is insulin-like growth factor type 1 (IGF-1) - a protein that helps spur cells to multiply and has been implicated in the cancer process. Previous animal research has shown that calorie restriction reduces blood levels of IGF-1.

Scientists are now looking into whether the animal research on calorie restriction applies to humans. A trial sponsored by the National Institutes of Health is investigating how calorie cutting affects “biomarkers of longevity” in people, such as levels of blood sugar and insulin.

Anticipating the possible health benefits to people, one recent study tested whether alternate-day fasting was a feasible way for people to cut calories.

Those investigators found that while three weeks on the regimen did indeed help study volunteers slash calories and shed a few pounds, chronic crankiness was a significant obstacle.

The new findings, according to Hellerstein, suggest the possibility of health benefits from moderate calorie restriction, whether through generally eating less or “intermittent” fasting.

It’s “not realistic,” he said, to have people severely limit their calories over a lifetime in anticipation of possibly living longer.

SOURCE: American Journal of Physiology, Endocrinology and Metabolism, May 2005.