Slimming courses such as Weight Watchers provided freely on the NHS could play an important role in combating obesity, new research suggests.
A major study conducted in the UK, Germany and Australia showed that a year-long Weight Watchers programme was far more beneficial than helpful doctor's advice.
Obese and overweight patients referred to the programme lost twice as much weight as those offered "standard care".
Commercial weight loss schemes are already offered to many NHS patients, usually lasting around 12 weeks.
For the new study, 772 patients were either given 12 months free membership of Weight Watchers, or offered advice on health and slimming by a primary care team.
After a year those on the slimming programme had shed an average of 11lbs 4oz while patients receiving standard care lost 4lbs 13oz.
Participants assigned to Weight Watchers were also more than three times more likely to lose at least 5% of their bodyweight.
Dr Susan Jebb, from the Medical Research Council Human Nutrition Research Unit in Cambridge, led the study, which is published by The Lancet medical journal.
The authors wrote: "Data from our study suggest that referral by a primary health-care professional to a commercial weight loss programme that provides regular weighing, advice about diet and physical activity, motivation, and group support, can offer a clinically useful early intervention for weight management in overweight and obese people that can be delivered at large scale.
"Further research is needed to examine long-term weight loss maintenance, together with a formal analysis of cost-effectiveness."