Researchers of a comprehensive study say an abnormal gene, known as GAD2, that stimulates hunger is a cause of overeating and obesity among many people worldwide.
A team of Franco-British scientists carried out the research on about 1200 French people, roughly half seriously overweight and half not.
The study shows that the gene acts by speeding up the production of a neurotransmitter in the brain. When that transmitter, known as GABA, interacts with another molecule in the hypothalamus in the brain, people feel a craving for food.
The researchers said some have a more active form of the gene, in turn building up more GABA in the brain. This suggested the "overaccumulation of GABA drives the stimulus to eat further than normal, and is thus a basis for explaining why obese people overeat".
Clues to prevention
"Genetic factors alone can not explain the rapid rise in obesity rates in the world, but they may provide clues to preventative and therapeutic approaches that will ease the health burden associated with obesity," said Philippe Froguel from Imperial College and Hammersmith Hospital of London.
"Having identified this gene, it may be possible (in the next few years ) to develop a screening programme to identify those who may be at risk of becoming obese later in life, and take effective preventative measures," the senior author of the study, carried out at the Pasteur Institute in Lille, northern France, said.
Scientists compared the genes of 576 obese and 646 normal weight adults, discovering two different forms of the GAD2 gene.
One type of the gene was protective against obesity, while a mutated form increased the risk that someone would become severely overweight.
About 300 million people worldwide suffer from obesity, which is a leading cause of high blood pressure, cardiovascular disease and type two diabetes.