We recruited 1267 adults with overweight and obesity and randomly allocated them to one of three weight loss programmes: brief intervention (a self-help booklet), an open-group behavioural weight management programme (Weight Watchers) for 12 weeks, or the same programme for 52-weeks. Participants were followed up for 2 years, and we collected clinical measurements and self-reported data on psychosocial variables and health resource use at baseline, 3 months, 1 year and 2 years.

At 1 year, both behavioural programmes led to greater weight loss than the brief intervention, but the 52 week programme led to greater weight loss and greater reductions in risk markers for diabetes than the 12 week programme and the brief intervention. Participants in the 52 week programme still had lower weight that the other groups at 2 year follow up.

We modelled the impact of the three programmes over the next 25 years, assuming that everyone regained any weight they had lost by year 5. Over the 25 years, the 12 week programme was predicted to be cost-saving because the initial costs of the programme were outweighed by reductions in diseases incidence and associated healthcare cost. The 52 week programme was more expensive initially, but had greater health benefits than both other groups and was very cost-effective by the usual clinical standards.

For more information on the main findings of the trial you can read the full paper, read our news story, or  download the summary infographic

Estimates of the long term cost-effectiveness of these programmes is based on assumptions about weight regain in the medium-term. We are currently running a 5-year follow up study – WRAP UP – to test these assumptions. WRAP UP will provide the first objective data on 5-year weight trajectories and health outcomes following this type of scalable weight management programme. We will use this data to refine our estimates of the long-term impact on disease incidence and health-care resource use.