Some people who eat a high-calorie fat-rich diet remain slim, yet others pile on the weight.

A high-fat diet in some people causes the brain cells to become insulated from the body, say researchers.

This prevents vital signals, which tell the body to stop eating and to burn calories through vigorous activities or exercise, from reaching the brain, reports the Daily Mail.

A Monash University team from Australia said the findings provide a critical link in addressing the obesity epidemic.

Prof Michael Cowley, who led the study, said: 'These neuronal (brain cell) circuits regulate eating behaviours and energy expenditure and are a naturally occurring process in the brain.

'The circuits begin to form early in life so that people may have a tendency towards obesity even before they eat their first meal,' he said, according to a Monash release.

Eating a high fat diet causes more 'insulation' in the nerve cells, and makes it even harder for the brain to help a person lose weight.

Prof Cowley added: 'Obese people are not necessarily lacking willpower. Their brains do not know how full they are or how much fat they have stored, so the brain does not tell the body to stop refuelling.

'Subsequently, their body's ability to lose weight is significantly reduced.' Prof Cowley and his team collaborated with scientists from the Yale School of Medicine in the US, as well as teams from Cincinnati, New Jersey in US and Mexico and Spain.

For a period of four months, the researchers monitored the eating and body composition of groups of mice and rats.

They found that those with a neural predisposition to obesity gained 30 percent more weight compared to six percent of the group with obesity-resistant cells.