A randomized controlled trial found that after one year, those on Weight Watchers (WW; meetings and digital tools) who completed the study lost significantly more weight than those who received weight-loss advice from their physicians, which is standard care. Specifically, -14.6 lbs vs -7.2 lbs, respectively.
In this 2011 study published in The Lancet, 772 adults in the United Kingdom, Australia, and Germany (86.5% female, 47.3y, BMI 31.4 kg/m2)—those in the WW group were also 3 times more likely to lose at least 5% of their body weight, and 3.5 times more likely to lose at least 10% of their body weight, by 12 months, compared to those following advice from their primary care physician.
The greater weight losses in WW compared to standard care were accompanied by significantly greater reductions in waist circumference and fat mass, and greater improvements in blood sugar and cholesterol levels.
Source: Jebb SA, et al. Primary care referral to a commercial provider for weight loss treatment versus standard care: a randomised controlled trial. Lancet 2011;378:1485-1492.