PURPOSE: There have been few randomized controlled trials of commercial weight-loss programs. This ongoing study compares the effects of a self-help program and a commercial program on weight loss and other measures of obesity in overweight and obese men and women. SUBJECTS AND METHODS: We report the results of the first 26 weeks of a multicenter, randomized, 2-year study of 423 subjects who had a body mass index of 27 to 40 kg/m2. Subjects were randomly assigned to either a self-help program, consisting of two 20-minute sessions with a nutritionist and provision of printed materials and other self-help resources, or to attendance at meetings of a commercial program (Weight Watchers). Outcome measures were changes in body weight, body mass index, waist circumference, and body fat. Changes in serum homocysteine levels were measured in a subsample of participants during the first 12 weeks. RESULTS: After 26 weeks, subjects in the commercial program, as compared with those in the self-help program, had greater decreases in body weight [mean (± SD) -4.8 ± 5.6 vs -1.4 ± 4.7 kg] and body mass index (-1.7 ± 1.9 vs -0.5 ± 1.6 kg/m2, both P<0.001) in intention-to-treat analyses. Among subjects measured at week 26, mean waist circumference (-4.3 ± 10.5 vs -0.7 ± 12.7 cm) and fat mass (-3.8 ± 7.0 vs -1.5 ± 7.6 kg, both P<0.05) also decreased more among subjects in the commercial program. Mean serum homocysteine levels improved in the commercial program compared with self-help (-0.5 ± 1.3 vs 0.9 ± 1.8 μM, P<0.05). CONCLUSIONS: A structured commercial weight-loss program is more likely to be effective for managing moderately overweight patients than brief counseling and self-help. (C) 2000 by Excerpta Medica, Inc.