Effects of soy or whey protein on weight reduction in patients with obesity: An exploratory, three-arm, placebo-controlled, double-blind, randomized clinical trial

Abstract

Summary: Background & aim: Although weight loss programs including diet and exercise targeting patients with obesity are essential, the percentage of patients who successfully achieve weight loss is less than 10%. One cause of failure to achieve weight loss is a strong sense of hunger, which is difficult to sustain. Additionally, it is important to prevent a decrease in muscle mass. Various protein supplements have been used to overcome these problems. However, there is insufficient evidence to support this theory. This study aimed to evaluate the effect of soy or whey protein beverages in conjunction with general dietary and exercise therapies on weight loss. Methods: This placebo-controlled, double-blind, randomized clinical trial was conducted at Kobe University Hospital. Patients with obesity and at least one obesity-related complication were enrolled. Three arms of soy, whey protein, or a placebo were supplemented once a day for 12 weeks, in addition to the general guidance on dietary and exercise therapies in a weight loss program. Energy intake during the trial was calculated using the Food Frequency Questionnaire. The primary outcome was percentage change in body weight from baseline to 12 weeks. Results: Between March 2021 and April 2022, 44 patients were enrolled. No significant differences were observed in body weight, waist circumference, body composition parameters, resting energy expenditure, blood pressure, or metabolic indicators. However, the energy, protein, and lipid intakes calculated from the prescribed nutritional intake in the weight loss program were significantly lower in the soy protein group (control group vs. soy group; total energy [kcal] −121.0 ± 416.6 vs. −340.0 ± 487.0, respectively P = 0.016; protein [g] 8.5 ± 11.9 vs. −5.1 ± 14.7, P = 0.023; lipid [g] −5.1 ± 16.1 vs. −19.8 ± 18.2, P = 0.018). Conclusions: No significant weight loss was observed in the soy or whey protein group. However, in the soy protein group, it was possible to maintain a lower energy intake, and protein and lipid intakes decreased in post-hoc analysis. Although further investigation is necessary, extending the administration period may result in significant weight loss. Clinical trial registration: Japan Registry of Clinical Trials (identifier: jRCTs051200103).

Keywords

• Obesity
• Weight loss program
• High-protein diet
• Soy protein
• Hunger
• Satisfaction