Intake of soymilk-okara powder for 12 weeks decreases body fat and increases body muscle in Japanese adults: A single-arm intervention study

Background and objectives: Okara is a by-product of soymilk manufacturing and a rich source of protein and dietary fiber. Some animal model reports suggested that okara intake might increase lipid catabolism and decrease anabolism. Moreover, in a mouse model experiment diets supplemented with okara altered cecal microbiota. However, there are few reports of dietary okara intake for the long term in healthy humans. This study investigated whether dietary okara intake in the long term affects the body composition and the gut microbiota flora in healthy Japanese adults. Methods: 46 participants (women: 43) were enrolled. All the subjects ingested 15g of okara powder (Soymilk-okara powder, Kikkoman Soyfoods Company, Japan) every day for 12 weeks. The subjects' body composition was assessed per 4 weeks. At baseline and after intervention for 12 weeks, fecal microbiota percentages were measured (Techno Suruga Laboratory Co., Ltd., Japan). Results: The median total soymilk-okara powder intake during the intervention for 12 weeks was 1182g. All the subjects ingested more than 720g (15 g/day×4 days/week×12 weeks). There was no difference in nutritional intakes and exercise habits before and after the intervention. The weight of body muscle significantly increased, and the percentage of body fat significantly decreased at 4, 8, and 12 weeks after the intervention than at baseline. The percentages of Coriobacteriaceae, Lactobacillales, Clostridium cluster IV and Clostridium cluster XI in feces significantly decreased at 12 weeks after the intervention than at the baseline. Conversely, the percentages of Bacteroides in feces significantly increased at 12 weeks after the intervention than at the baseline. Therefore, the Firmicutes group / Bacteroidetes group ratio in feces significantly decreased at 12 weeks after the intervention than at the baseline. Conclusions: A dietary intake of 15g of soymilk-okara powder for 12 weeks induced a decrease in body fat, an increase in body muscle, and a change in fecal microbiota flora.