Adults referred to the commercial weight loss programme Weight Watchers shed twice as much weight as people who received standard care over a 12-month period, according to a study published Thursday.

In clinical trials, researchers led by Susan Jebb of the UK Medical Research Council assessed 772 overweight and obese adults in Australia, Germany, and Britain.

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.

Overall, individuals in Weight Watchers lost around twice as much weight as did those in the other group, a mean loss of 5.1 kilograms versus 2.2. Among those who stuck with either program to the end, the figures were 6.7 against 3.3 kg, respectively.

Participants randomized to Weight Watchers were also more than three times as likely to lose at least five percent of their body weight, said the study, published in The Lancet.

Weight Watchers offers weekly weighing and group support. It also promotes a balanced, reduced-energy diet along with increased physical activity.

Primary care providers -- sometimes nurses, sometimes doctors -- generally offer weight-loss treatment in line with national guidelines, but vary in the level of supervision.

"The similar weight losses achieved in Australia, Germany, and the UK implies that this commercial program, in partnership with primary care providers, is a robust intervention that is generalizable to other economically developed countries," the researchers concluded.

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 program.

"Further research is needed to examine long-term weight loss maintenance, together with a formal analysis of cost-effectiveness," they added.