Of 141 adults (90% female, 49.7y, BMI 36.2 kg/m2), those who followed Weight Watchers (WW; meetings and digital tools) for 48 weeks lost a statistically equivalent amount of weight as those who followed a professionally delivered behavioral weight-loss program (BWL). Specifically, -13.2 lbs vs -11.9 lbs, respectively.
The results of this 48-week randomized controlled trial, published in a 2013 issue of Obesity, also found that three times as many people in the WW meetings lost 10% or more of their body weight by 48 weeks than those who attended the professionally delivered weight-loss program (36.7% vs 13.0%, respectively).
Source: Pinto AM, et al. Combining behavioral weight loss treatment and a commercial program: a randomized clinical trial. Obesity (Silver Spring). 2013;21(4):673-680.