Fat-fighting genes that protect millions from obesity have been discovered in a major research project.
Scientists at Cambridge University say drugs to keep people slim are now a possibility after they identified the handful of genetic factors that prevent overeating.
Doctors knew that genes could influence a person's weight.
However, the new study is significant because it reveals in granular detail which variants suppress or encourage appetite.
"This study drives home the fact that genetics play a major role in why some people are obese - and that some people are fortunate enough to have genes that protect them from obesity," said Professor Sadaf Farooqi, who led the project.
"It doesn't mean that we can't influence our weight by watching what we eat.
"But it does mean the odds are stacked against some people and in favour of others," she added.
The research team analysed the genetic profiles of more than half-a-million volunteers from the UK Biobank.
They found that around 6pc of British people with European ancestry have a combination of genes that means that they are less likely to put on weight, regardless of their lifestyle.
Published in the journal 'Cell', the study focused on a gene known as the MC4R which was previously identified by the Cambridge scientists to play a role in appetite by controlling a receptor in the brain, that is called melanocortin 4.
People who had certain variants of MC4R that disrupted this receptor tended to gain weight easily, the study found.
Participants with these variants would eat less, which was thought to explain their lower weight.
The insight forms a platform for the development of new drugs which mimic the newly identified pathway.