Patients referred by their doctors to Weight Watchers were found to lose about twice as much weight over a year as those on a standard weight-loss program, medical researchers say.

In a study published on The Lancet's Web site Wednesday, researchers led by Susan Jebb of the UK Medical Research Council assessed 772 overweight and obese adults in Australia, Germany and Great Britain.

The randomized control trial provided compelling evidence that Weight Watchers was twice as effective as a commercial weight-loss program with standard medical care.

About half the patients received a year's standard care, while the other half were given a 12-month free membership for a Weight Watchers group near their homes.

Sixty-one percent of the participants assigned to the commercial program completed it, while 51 percent of the standard care group finished their program.

The researchers emphasized the important role of family doctors and primary health care providers in giving advice and in making referrals to commercial weight-loss programs.

Obesity affects males and females of all ages in wealthier countries and is becoming more common among poorer people. In low-income nations, obesity appears to be more common in adults of middle age, especially wealthy urban females.

Approximately 1.5 billion adults worldwide are overweight, of which 500 million are obese; 170 million children are overweight globally. In the United States, obesity has overtaken smoking as the leading preventable cause of disease.

A weight loss of 5 to 10 percent may lower the risk of diabetes, heart disease and other diseases.

Such weight loss isn't going to transform how people look, noted Jebb, head of diet and population health for the Medical Research Council, a British government-funded research unit.