It is a known fact that eating junk food causes bulging waistlines in adolescents. But a study by the UPV/EHU-University of the Basque Country has found that abdominal fat cannot be reduced even if they engage in more physical activity.

Researchers said that the only way to fight obesity is through a combination of diet with lower fat content and lots of exercise.

"Until now it was thought even with an unbalanced diet, you somehow compensated for it if you got plenty of physical exercise," researcher Dr Idoia Labayen said in a press release. "Adolescents are a risk group as far as lifestyles are concerned because they are starting to take their own decisions about what they want and do not want to eat, and they are also going through a period in which many of them have stopped doing any sport."

For the study, the researchers observed the role of dietary fat in abdominal fat accumulation in 224 adolescent participants. The build-up of fat around the stomach is considered to be the most dangerous as it heightens risk of developing cardiovascular problems, diabetes, high blood pressure and high cholesterol.

They calculated fat content in different areas of the body using a machine called Dexa (dual energy X-ray absorptiometry). Dietary habits and physical activity levels were also taken into account.

The researchers found that participants who were on a fat-rich diet gained more weight around their waist irrespective of whether they played too many sports. The finding therefore establishes a strong link between dietary fat and abdominal fat.

"Despite the fact physical activity is usually a prevention factor, in this particular case it is not able to counteract it. So 'these results point to dietary fat content as a key risk factor in abdominal adiposity in adolescents, no matter how much physical exercise they do," Labayen said.

The study has been published in Clinical Nutrition.