Scientists at the University of Dusseldorf in Germany say that they may have unravelled the mystery as to how some people can eat and never put on weight, while others struggle to shed a single ounce may have finally been solved by scientists.
Research leader Dr. Ulrich Ruther says that a gene called FTO appears to be behind these differences.
During a study, the researchers observed that the mice that lacked the FTO gene remained thin despite eating large amounts of food and being inactive, which suggested that they were burning up energy faster than the animals that had a functioning gene.
It is thought the gene may limit the amount of energy given off in the form of heat.
"Genetic variation close to the FTO gene is definitely associated with obesity in humans, but, until now, it was not clear whether this genetic variation was likely to influence obesity by altering the expression or function of the FTO gene itself or some neighbouring gene," the Telegraph quoted Professor Stephen O'Rahilly, a metabolism expert from Cambridge University, as telling Nature magazine.
"This work shows that if mice lack the FTO gene they are very lean because they spontaneously burn off enormous amounts of energy.
"This is a bit puzzling as several recent studies have suggested that the variant in the human FTO gene that increases the risk of obesity has effects on appetite and food intake but does not seem to have any effect on how quickly energy is burned off.
"So, this work provides a crucial piece of evidence supporting the notion that the FTO gene itself is likely to be involved in the effects of common human genetic variants on body fat," O'Rahilly added.
The researchers believe that their breakthrough study may pave the way for a raft of new treatments for obesity.
Dr Ruther said: "This finding will promote research into the development of drugs that modulate FTO activity. We strongly suspect that, in man, FTO might have more complex effects on both food intake and energy expenditure than has been so far suggested and that it is still not clear what the overall effect of inhibiting FTO in humans would be."