Scientists believe they may have discovered why some people have problems controlling their appetite.
The brain plays a key role in regulating appetite
Experts at Warwick University say it may be down to poor communication between key brain cells.
They have identified a group of neurons that appear to play an important role in telling people when to eat.
But writing in Nature Neuroscience they said the process is so complicated there is a huge potential for problems which may cause people to over-eat.
Dr Dave Spanswick and colleagues looked at a part of the brain called the hypothalamic arcuate nucleus.
This area deals with hunger and also sends out signals to tell people when they have eaten enough. However, the mechanism behind it is poorly understood.
The scientists looked in particular at a group of neurons that produce regular bursts of electrical activity.
They found that these neurons, which they dubbed ARC pacemakers, appear to regulate the drive to eat.
They also discovered that these neurons act on information supplied by a wide variety of body signals.
They process information from hormones and other chemicals telling them if the body needs energy and food.
The scientists say the mechanism is extremely complicated. So much so, the possibility of something going wrong is quite high.
"In the past, people with a weight problem have faced scepticism and doubts as to how hard they were really trying to stick to diet and exercise regimes," said a spokesman for the research team.
"This research shows that there may indeed be very good reasons why they seem unable to solve their weight problems simply by employing the usual methods - eating less may be a more difficult and complicated problem than we currently anticipate."
Researchers at the universities of Edinburgh and Newcastle-upon-Tyne are also carrying out research in this area.
Their five-year project will examine if the brain "re-programmes" itself when people become overweight causing them to continue to eat too much and making it hard for them to cut down.
Jonathan Seckl, professor of molecular medicine at Edinburgh, said there is now growing evidence that genes and the brain can play a role in obesity.
"We now know that if some genes go wrong, they can cause obesity," he told BBC News Online.
"They can interfere with how the brain deals with signals that drive appetite. However, this only happens in a tiny minority of people who are overweight."