Based on data from a sample of 2275 children from the Bristol-based ALSPAC study (Children of the 90s), the current study suggested that people might be able to avoid becoming obese if they adopted a healthier diet with a low energy density.

The researchers said that such a healthy diet could even benefit those who carry the FTO gene, identified as being a high-risk gene for obesity.

Dietary energy density (DED) refers to the amount of energy consumed per unit weight of food, or number of calories per bite.

A low dietary energy density can be achieved by eating lots of water-rich foods like fruits and vegetables, and by limiting foods high in fat and sugar like chocolate and biscuits.

The study focused on how DED affected the build up of fat in the body over a period of three years in children aged between 10 and 13 years old.

And the researchers found that children with a more energy dense diet (more calories per bite) tended to have more fat mass three years later, and also confirmed that those carrying the high risk gene had greater fat mass overall.

After looking at whether children with the FTO gene had a stronger reaction to an energy dense diet than children with a lower genetic risk, the researchers found that they did not.

The results indicate that if a child with a high genetic risk eats a diet with fewer calories per bite, they may be able to offset the effect of the gene on weight gain and so stay a healthy weight.

"This is an important finding because it provides evidence that it’s easier to eat too much energy and gain weight when your diet is packed tight with calories, so adopting a diet with more bulk and less energy per bite could help people avoid becoming obese regardless of their genetic risk. Obesity is not inevitable if your genes give you a higher risk because if you change the types of foods you eat this will help curb excessive weight gain,” said lead author Dr Laura Johnson, UCL Epidemiology and Public Health.