Want to keep the weight off? Get on your bike

Just five minutes of riding a bicycle each day can help a younger woman keep the pounds off, US researchers reported yesterday in a study offering one potentially easy way to help Americans slim down.

The heaviest women benefited the most, the team at the Harvard School of Public Health and Brigham and Women's Hospital in Boston reported.

"Small daily increments in bicycling helped women control their weight. But the more time women spent bicycling, the better," said Harvard's Rania Mekary, who worked on the study.

"Women with excess weight appeared to benefit the most. This is encouraging for women with weight problems because they could substitute bicycling for slow walking or car driving."

The research could help public policymakers trying to find ways to slow the US obesity epidemic, the researchers wrote in the Archives of Internal Medicine.

Two-thirds of US adults are overweight or obese and 16% of children and adolescents are overweight.

The accompanying disease burden costs billions and president Barack Obama has assigned his wife Michelle Obama and cabinet secretaries to find ways to counter this trend.

Their plan includes changes to neighbourhoods and cities to make it easier for Americans to exercise.

Mekary's team studied 18,414 healthy women who had not yet gone through menopause taking part in the Brigham and Women's hospital-based nurses' health study, an ongoing study of women's health over time.

On average, the nurses gained about 20 pounds (9.3 kg) over the 16-year period.

The women who did not bicycle in 1989 who had started by 2005 were a quarter less likely to have gained weight, even if they rode for just five minutes a day, the researchers said.

Comparatively, women who started out exercising on bikes for more than 15 minutes day in 1989 but who slacked off over time gained weight.

Overweight and obese women who were bicycling just two or three hours a week were 56% less likely to gain weight.

"Unlike discretionary gym time, bicycling could replace time spent in a car for necessary travel of some distance to work, shops or school as activities of daily living," the researchers wrote.

"Bicycling could then be an unconscious form of exercise because the trip's destination, and not the exercise, could be the goal."