Ahern et al. BMC Public Health 2011, 11:434 http://www.biomedcentral.com/1471-2458/11/434 commercial weight loss diets, conducted as part of a BBC series, mean weight change among self-selected participants at 2 months ranged from -3.8% to -5.5% initial weight for the various diets vs. -0.4% for controls and -4.9 to -7.3% at 6 months vs. +0.6% for controls [9]. In the present analysis over 54% of commenced refer- ral courses were completed. High drop-out rates are usually observed in studies of obesity treatment, particu- larly those conducted outside of a research centre envir- onment. In the Counterweight study, retention was 47.7% at 3 months, 30% at 6 months and 22.5% at 12 months [8] and in controlled trials, where retention is likely to be higher than in general practice, drop-out rates range from 10-80% [10]. In the UK, the NHS (primarily through PCTs) can currently purchase referral packages for 12 WW ses- sions, which can then be prescribed to patients at no charge. These 12 session referrals are expected to be completed over approximately 12 weeks, although many participants completed their sessions over a longer per- iod of time. There was a trend for weight loss to dimin- ish as the period of time to complete the 12 sessions increased beyond the 12-week reference period, perhaps reflecting declining adherence. However, absolute weight loss was greatest in the 5% of participants where the final weight was recorded more than 24 weeks after baseline, perhaps reflecting a small group of committed participants who return for a final weigh-in and who have had a longer period in which to lose weight. Twelve weeks is a relatively short duration for a weight management programme, and data on the longer term outcomes of these referrals is necessary to establish whether this treatment has a significant impact on long term health outcomes. Research suggests that in many cases the weight lost during behavioural and pharmacolo- gical treatments is regained after treatment cessation [5,11-13]. A quarter of referrals were repeat referrals for the same patient and although weight loss diminished with repeat referrals these patients did achieve additional weight losses, suggesting that longer referrals might improve weight loss. However, increased treatment duration leads to increased costs of intervention and the longer-term impact beyond the duration of the programme still needs to be established for both commercial weight management programmes and those led by the NHS, including analyses of the cost-effectiveness of each approach. Data was not available to calculate the cost-effectiveness in the current study. However, the current cost to PCTs of the 12 session package is £45 + VAT, which is likely to be lower than for programmes led by health professionals. One study in Australia examined the cost-effectiveness of referral to a six-month course of Weight Watchers and a weight loss treatment programme developed by a health service and concluded that neither treatment was cost Page 4 of 5 effective [14]. However, this study did not base their calcu- lations on the cost of referral packages offered to health care providers, and the authors acknowledge substantial uncertainty in their estimates and highlight the fact that, due to lack of data, they were unable to include potential health benefits additional to those resulting directly from weight loss, such as benefits derived from changes to diet and physical activity as a result of the programme. Although this study used weight loss data from a small UK study, cost data was derived from an Australian pri- cing structure and may not reflect the true cost-effective- ness of WW referral in the UK and other countries, and further evaluation is therefore warranted. In addition to averted healthcare costs arising from avoidance of treat- ment of modelled diseases, these further evaluations should also consider the considerable costs of obesity to the wider society, including time off work as a result of obesity-related illness. They should also consider compari- son with alternative treatments such as individual-level primary care-based intervention. The proportion of men referred to WW was very low, which may reflect the perception of the scheme by either prospective participants or practitioners as more suitable for women. However, weight loss in men who did attend was similar to that of women. This could suggest that the programme is equally effective in men and women, but may also reflect a tendency for men to only commence a referral if they are committed to adhering to the pro- gramme and the format is appealing to them. Further research should examine the origin of this gender bias. Participants with a BMI between 30 and 35 kg/m lost significantly more weight compared to those with a BMI < 30 kg/m. However most of these participants will require further weight loss interventions to achieve continued reductions in excess weight. Those with a BMI >40 kg/m lost less weight than those with a BMI < 30 kg/m. Despite the large number of referrals made in this weight category, this low intensity treatment may be insufficient for this level of obesity. We speculate that the referral of heavier patients may reflect a paucity of available treatment options in primary care. Limited data from repeat referrals suggests that additional weight loss is possible, but more intensive interventions may be warranted as second-line therapy for some participants at greatest risk. This observational study was an audit of practice-based data, so there was no control group. Further research using randomised controlled trials is needed to examine the long-term clinical outcome and cost effectiveness of WW relative to interventions led by health professionals. However, there is a dearth of research into treatment of overweight and obesity in primary care in the UK and what little there is is generally small in scale and primarily audit based or pilot data [15-17]. This study is the largest audit of a commercial weight loss programme working in