People with mutations in the FTO gene had higher levels of ghrelin in their blood, which made them feel hungry soon after eating a meal, and could help to explain why they eat more and choose higher-calorie foods.
Everyone has two copies of the FTO gene, and the 16 percent of the population with genetic defects in both copies have a 70 percent higher chance of being obese. Almost half of people have one FTO gene mutation, and are 30 percent more likely to be obese.
Dr Rachel Batterham from University College London, who led the study, explained: 'What this study shows us is that individuals with two copies of the obesity-risk FTO variant are biologically programmed to eat more'. She added: 'Not only do these people have higher ghrelin levels and therefore feel hungrier, their brains respond differently to ghrelin and to pictures of food – it's a double hit'.
The study compared samples of two groups of men of normal weight: one with two copies of the high-risk FTO gene, and the other with two copies of the gene thought to cause low risk of obesity. Although levels of ghrelin usually fall after eating and remove feelings of hunger, blood samples revealed that the hormonal levels rose more quickly after meals in the high-risk patients.
Additionally, a series of brain scans in 24 men showed that these two groups responded differently to pictures of food. Men with the high-risk genes found pictures of higher-calorie foods more appealing than those with the low-risk variation.
Understanding how FTO affects the odds of becoming obese could help patients manage their weight. Dr Batterham said: 'We know that ghrelin, and therefore hunger, can be reduced by exercise like running or cycling or by eating a high-protein diet'.
Professor Steve Bloom from Imperial College London commented on the results, saying: 'Slowly we are discovering the factors which make us overweight and this study, encompassing not only demonstration of a higher level of hunger hormone, ghrelin, but also changes in the brain associated with ghrelin's action, is an important step forward. Already pharmaceutical companies are working on ghrelin antagonists and this will further spur on that effort and perhaps indicate whom best to treat'.
These findings shed some light on why people who have a variation of this gene are more likely to be obese – a question that has been unanswered until now. However, NHS Choices points out that 'this was a small study and the implications of these findings are unlikely to have any immediate impact on solving the obesity problem'.