(Agencies)
Updated: 2008-02-19 16:05

People who exercise 60 to 90 minutes a day shed weight and keep it off It will make unpleasant reading for dieters who have been hoping that light exercise was the key to weight loss.

For it seems the most successful slimmers chalk up a marathon a week, according to research.

A study found that those who exercised for 60 to 90 minutes a day - walking the equivalent of a marathon each week - tended to shed at least two stones and kept the weight off for six years.

The data contradicts the popular theory that gentle exercise is enough to stay slim.

The American Association for Advancement of Science's conference on Sunday also heard fresh calls from a British expert for a more urgent global response to the obesity crisis.

Professor Philip James, chairman of the International Obesity Task Force, believes the obesity epidemic is now too serious to be treated as a "lifestyle choice" issue.

"Just as the threat of climate change has begun to be taken seriously when it may be almost too late, the threat of an obesity-related health disaster around the world needs urgent action because, like climate change, its effects are exceptionally difficult to reverse," he said.