Dr. Magdalena Cuenca-García, of the Department of Medical Physiology in Granada University's School of Medicine, and colleagues report their findings in a recent online issue of the journal Nutrition.
The researchers are part of the HELENA study group, which is collecting and analyzing data about the diets, fitness and various health measures among European adolescents.
Previous studies have already found that regular chocolate consumption is linked to leanness in adults. There is also evidence that eating chocolate may reduce cardiovascular disease risk.
The Spanish researchers decided to use the HELENA data to see if the same could be said of teenagers.
They analyzed records on 1,458 adolescents from nine European countries who were aged from 12-17 and who had completed computer-based questionnaires asking them to recall what they had eaten in the previous 24 hours on two non-consecutive days.
The records also contained information from which they could assess participants' BMI, waist circumference, body fat measures and activity levels.
The results showed that higher chocolate intake among the teenagers was linked with lower levels of total fat and fat around the middle, regardless of other factors (including exercise).
The researchers in this study did not examine why chocolate appears to help the youngsters stay slim, but some previous studies have suggested it could be something to do with the flavonoids it contains.
Flavonoids are a group of polyphenolic compounds known to have numerous beneficial biochemical and antioxidant effects. For example, they appear to protect against cardiovascular disease through antioxidant, anti-clotting and anti-inflammatory properties.
"It's also possible that flavonoids in chocolate may decrease blood concentrations of bad cholesterol and reduce blood pressure," says Dr. Susanna C. Larsson, of Sweden's Karolinska Institute, where she and her team conducted a study of Swedish men that found chocolate consumption may also lower stroke risk.
Many researchers say it is dark chocolate that is good for the heart, but Dr. Larsson says, surprisingly, that 90% of the chocolate eaten in Sweden -- as they also found in their study -- is milk chocolate.