Overweight people who believe exercise alone can make them thin are living under an illusion because only serious, long-term dieting can lead to significant weight loss, a study has found.
The belief that exercise can be used to fight the obesity epidemic is wrong because it would require inordinate amounts of heavy physical training over long periods of time to have any significant impact on a person's weight, scientists said.
Professor John Speakman of the University of Aberdeen said: "The evidence is that exercise is not sufficient to reverse the obesity epidemic. The only way we're going to reverse it is to reduce the amount of food intake.
"It is important for policy makers to realise that, if they want to promote weight loss in overweight and obese people, the most effective way to realise this is through promotion of healthy eating practices, not through exercise regimes," he said.
One in five people in Britain is classed as clinically obese and 61 per cent of the population is overweight.
Professor Speakman said popular ideas about obesity are wrong because studies have shown that levels of physical activity have not changed over the past 25 years, while obesity rates have risen dramatically. "To lose the 300 calories contained in a sandwich would require someone to run for an hour. To bring the weight of a person who falls into the obese category down to normal levels would require them to walk for between four and five hours a day."