Children carrying a gene associated with obesity "struggle to recognise when they are full", researchers have discovered in a study of more than 3,000 UK children.
The gene, known as FTO, is strongly associated with obesity. However, it was not known whether it affects weight by influencing the amount of food eaten or the amount of calories burnt off.
The results of a new study, led by researchers at University College London and King's College London, strongly suggest that the gene works by modifying appetite, so that the children in the study who had two copies of the higher-risk FTO gene are less likely to have their appetite "switched off" by eating.
The researchers say that the finding, published in the Journal of Clinical Endocrinology & Metabolism, helps to unravel the mechanism of the genetic basis of obesity.
The researchers tested whether children carrying the higher risk gene had altered appetite in a sample of 3,337 unrelated children aged 8–11 years old.
Part of the research asked parents to complete a specially designed questionnaire about their children's eating habits, to assess aspects such as their child's enjoyment of food and how easily they became full.
FTO is the first common obesity gene to be identified in Caucasian populations. Previous studies have shown that adults with two copies of the FTO gene are on average 3kg heavier, and individuals with a single copy are on average 1.5kg heavier, than those without the gene.
Lead author of the study, Professor Jane Wardle, UCL Epidemiology & Public Health, said: "While recent research has shown that the FTO gene is strongly linked with children's body weight and food intake, this study tells us more about how the gene could be exerting its effect.
"What we have shown is that children with the 'risky' variants of the gene have weaker satiety responses – meaning they don't just overeat, but they struggle to recognise when they are full.
"It is not simply the case that people who carry the risky variant of this gene automatically become overweight – but they are more susceptible to overeating.
"This makes them significantly more vulnerable to the modern environment, which confronts all of us with large portion sizes and limitless opportunities to eat."