People who eat chocolate frequently tend to have a lower body mass index than those who don't eat it as often, U.S. researchers have found.

For the study in Monday's online issue of the Archives of Internal Medicine, researchers asked 1,017 healthy men and women aged 20 to 85 how many times a week they ate chocolate. Participants also filled in questionnaires about their diet and lifestyle.

Researchers are calling for a randomized trial to test the potential metabolic benefits of chocolate in humans. (Vasily Fedosenko/Reuters )

Study author Dr. Beatrice Golomb, a professor in the medical department at the University of California, San Diego, advised people to feel less guilty about indulging in the sweet treat.

"I joke that chocolate is my favourite vegetable," Golomb said in an email.

In the study, Golomb and her colleagues concluded that adults who ate chocolate more frequently had a lower BMI than those who ate it less often.

Earlier studies suggested that chocolate has beneficial effects on metabolism, which may extend to lower body mass index, the researchers said.

In human experiments, chocolate showed benefits for insulin sensitivity, blood pressure and cholesterol levels.

Quality of calories

To explore how the rich dessert may help, the researchers considered factors like the saturated fat content of chocolate, calories, physical activity levels and mood.

Only frequency of chocolate consumption made a strong enough difference to be a statistical association, and the researchers cautioned against presuming there's a cause-and-effect relationship between eating chocolate and lower body mass.

But the chocolate finding supports a growing body of literature that suggests it's the quality not only the quantity of calories that matter for metabolic syndrome, which includes a high BMI.

Scientists suspect that antioxidants in cocoa help protect the energy-producing mitochondria that power cells.

Some compounds in chocolate may increase the number of mitochondria and increase production of small blood vessels that allow oxygen and nutrients to be delivered better, which may also help metabolism, Golomb said.

The researchers called the finding "intriguing" enough to request a randomized trial testing the potential metabolic benefits of chocolate.

Dietitians advise savouring small amounts — just a few squares a day — of chocolate with a cocoa content of 70 per cent or more.

The study was funded by the U.S. National Heart, Lung and Blood Institute and the University of California.