Effects of consuming a high‐protein diet with or without soy protein during weight loss and maintenance: a non‐inferiority, randomized clinical efficacy trial

OBJECTIVE: This 12‐month randomized, non‐inferiority clinical trial sought to determine the impact of consuming soy protein as part of an energy‐restricted, high‐protein diet on weight loss, body composition and cardiometabolic health. METHODS: Seventy‐one adults (58 female) with overweight or obesity (body mass index: 32.9 ± 3.6 kg m(−2)) were randomly assigned to consume three servings of soy (S) or non‐soy (NS) protein foods per day for 12 months. All participants completed a group‐based behavioural weight loss program lasting 4 months (M4), and follow‐up assessments were completed at month 12 (M12). RESULTS: Body weight was reduced in both groups at M4 (S: −7.0% ± 5.2%, NS: −7.1% ± 5.7%) and M12 (S: 3.6% ± 5.1%, NS: −4.8% ± 7.3%). Body weight reductions (mean difference [90% confidence interval]) were not different between S and NS at either time point (M4: −0.16% [−1.4, 3.6], P = 0.90; M12: 1.1% [−1.4, 3.6], P = 0.44). Differences in body fat mass loss were not different between S and NS at M4 (0.29 ± 0.84 kg, P = 0.73) or M12 (0.78 ± 1.5 kg, P = 0.59). Weight loss‐induced improvements in cholesterol, triglycerides and blood pressure did not differ between S and NS. CONCLUSION: These results indicate that soy‐based protein foods can be effectively incorporated into an energy‐restricted, high‐protein diet for improving body weight, body composition and cardiometabolic health.