Rates of obesity are on the rise
Seven new gene variants discovered by scientists suggest strongly that obesity is largely a mind problem.
The findings suggest the brain plays the dominant role in controlling appetite, and that obesity cannot easily be blamed on metabolic flaws.
Two international studies, published in Nature Genetics, examined samples from thousands of people for the tiniest genetic changes.
Many of the seven key variants seem to be active in the brain.
This suggests that the brain's impact on appetite and eating behaviour may be more important that any genetic variation which alters the body's ability to lay down or burn up fat.
All seven variants were picked up by a study led by Icelandic company deCODE Genetics, while six of the seven were also identified in a second, independent study by an international team dubbed the Giant consortium.
In both cases the researchers scrutinised DNA samples from thousands of people to assess the impact of tiny changes.
Each of the variants identified had a small impact on obesity, but a person carrying all of them was typically around 1.5kg - 2kg heavier than average.
It is estimated that as much as 70% of the variation in body mass index - a measure of obesity based on height and weight - is down to genetics, rather than environmental factors.
Researcher Dr Kari Stefansson, of deCODE Genetics said: "This suggests that as we work to develop better means of combating obesity, we need to focus on the regulation of appetite at least as much as on the metabolic factors of how the body uses and stores energy."
Major step forward
Dr Alan Guttmacher, of the US National Human Genome Research Institute, said the research was a major step forward in understanding how the human body regulates weight.
However, Professor Peter Weissberg, of the at the British Heart Foundation, expressed caution.
He said: "This research adds to the growing body of evidence that some people are more at risk of becoming obese because of their genes.
"It suggests that some people may be less able than others to resist the temptation to overeat because of their genetic background and it might start to explain why some people have no problem keeping their weight down whilst others struggle.
"However, this cannot be the explanation for the current epidemic of obesity since these genes have been present for centuries and the obesity epidemic is a relatively new phenomenon."
Almost one in four people in the UK is now classified as obese, and expert predict the proportion will continue to rise sharply.