Soy compared to casein meal replacement shakes with energy-restricted diets for obese women: randomized controlled trial

Recent studies suggest that obese individuals lose weight more rapidly and lose more total weight with soy protein than with animal protein as a major diet component. The purpose of the present study was to evaluate the weight-loss efficacy and changes in body composition, waist circumference, blood pressure, and levels of plasma glucose, insulin, serum lipids, C-reactive protein, and homocysteine from consumption of either 3 soy shakes or 3 casein shakes daily as part of a 16-week, energy-restricted diet for obese women. Forty-three women with body mass index values of 30 to 40 kg/m2 were randomized to intensive dietary interventions using either casein (n = 21) or soy (n = 22) shakes. Subjects were instructed to consume 3 shakes, 1 prepackaged entrée, and 5 servings of fruits or vegetables daily to achieve an energy intake of 4.5 to 5.0 MJ/d. Subjects attended classes weekly or biweekly. Weight, body fat, lipid, and glucose measurements were obtained at baseline and at 8 and 16 weeks. For both groups combined, subjects lost 8.1% of initial body weight (7.7 kg) at 8 weeks and 13.4% (12.7 kg) at 16 weeks. Weight loss from baseline did not differ significantly by group and, for completing subjects, was 14.0% ± 1.2% (mean ± SE) for casein and 12.8% ± 1.4% for soy. With the intention-to-treat analysis, weight losses at 16 weeks were 12.5% ± 1.4% for casein and 11.3% ± 1.2% for soy. Body fat losses were 23.7% ± 2.0% for casein and 21.8% ± 2.4% for soy and did not differ significantly. Both study groups lost significant amounts of weight with a highly structured behavioral program incorporating 4 meal replacements and vegetables and fruits. Differences in weight loss and body composition changes between casein and soy treatments were not significant.