When 100 schoolchildren aged from four to 10 were given an identical meal, those with the gene ate more of the calorie-dense foods (cheese, crisps, chocolate) containing more fat and sugar and less of the healthy foods (grapes, cucumber) than those without.
The scientists, from the University of Dundee, found the gene made no difference to the rate at which the children burnt energy or to their level of physical exercise.
There was also no evidence that it affected how much they needed to eat to feel satisfied. The results are published in the New England Journal of Medicine.
The study was led by Professor Colin Palmer, who was part of a group of British scientists who identified the obesity gene, FTO, in 2007.
They found people carrying one copy of a variant of the gene (49 per cent) had a 30 per cent increased risk of obesity. Individuals carrying two copies (14 per cent) had a 70 per cent increased risk.
Source: The Independent