Chocolate may not be as hazardous to your waistline as you think — at least in moderation.

A new study shows that people who eat chocolate frequently have lower body mass indexes than those who eat it less often. The researchers could not explain precisely why something usually loaded with sugar, fat and calories would have a beneficial effect on weight. But they suspect that antioxidants and other compounds in chocolate may deliver a metabolic boost that can offset its caloric downside.

Chocoholics may know that in recent years chocolate has been linked to a growing list of health benefits. Studies have found, for example, that regularly eating chocolate may lower blood pressure and cardiovascular risk, andimprove cholesterol and insulin regulation.

Although the new study is among the first to look at chocolate’s effect on weight, the findings “are compatible with other evidence showing favorable metabolic effects that are known to track with body mass index,” said Dr. Beatrice A. Golomb, lead author of the study and an associate professor of medicine at the University of California, San Diego.

Dr. Golomb’s study, published in Archives of Internal Medicine and financed by the National Institutes of Health, involved roughly 1,000 adults. The researchers looked at data on how often they exercised, the amount and type of calories they ate — including a breakdown of the types of dietary fat they consumed — and how their health and weight related to their chocolate intake. On average, the subjects were middle-aged, exercised about three times a week and ate chocolate about twice a week. There was no breakdown of the kinds of chocolate they ate, whether dark, milk or white.

The people who ate chocolate the most frequently, despite eating more calories and exercising no differently from those who ate the least chocolate, tended to have lower B.M.I.’s. There was a difference of roughly five to seven pounds between subjects who ate five servings of chocolate a week and those who ate none, Dr. Golomb said.

Dietary studies can be unreliable, since so many complicating factors can influence results, and it is difficult to pinpoint cause and effect. But the researchers adjusted their results for a number of variables, including age, gender, depression, vegetable consumption, and fat and calorie intake. “It didn’t matter which of those you added, the relationship remained very stably significant,” said Dr. Golomb.

Still, the findings should not be taken as a license to overindulge in chocolate eggs and bunnies this Easter. Dr. Golomb cautioned that it was the frequency of chocolate consumption — not the amount per serving — that had a beneficial effect on B.M.I. Indeed, there was a small trend toward higher B.M.I.’s among those consuming larger amounts of chocolate per sitting.

“It’s not the case that eating the largest amount of chocolate is beneficial; it’s that eating it more often was favorable,” Dr. Golomb said. “If you eat 10 pounds of chocolate a day, that’s not going to be a favorable thing.”

The idea for the study came to Dr. Golomb a few years ago at an American Heart Association conference, when Dr. Golomb was sitting next to a nutritionist who studies chocolate. “This lovely chocolate dessert cart came out, and she looked at it forlornly and said, ‘Too bad it has all these calories,’ ” she recalled.

Dr. Golomb was familiar with research on animals showing that polyphenols, a type of antioxidant found in abundance in chocolate — particularly dark chocolate — increased muscular performance and lean muscle mass and could reduce weight without changes in calorie consumption or exercise levels. That, along with the research on humans showing all the other benefits that tend to go along with improved fitness, including lower blood pressure and better regulation of insulin, led Dr. Golomb to suspect that the calories in chocolate would be offset by improvements in metabolism. So the net result of eating chocolate on body weight, she thought, would be a neutral one.

“We found something slightly more favorable than that,” she said.

Dr. Golomb said she had not yet spoken to the nutritionist who inspired the study to tell her about the findings. “I should probably give her a call,” she said.