Fermented Soybean Suppresses Visceral Fat Accumulation in Mice.

SCOPE: Mice are fed a soybean diet before or after fermentation in the present work to allow direct comparison of the antiobesity effect of fermentation. METHODS: C57BL6J mice were fed high-fat diets containing boiled soybeans (prefermentation) or Natto (postfermentation) for 4 weeks. Prefermented cooked soybeans or Natto was added at levels of 2.5 and 5%, which are the amounts that can be ingested in a normal diet once and twice a day. In addition, mice gut microbiota from fecal samples were analyzed to explore the mechanisms of effects caused by fermentation. RESULTS: Natto intake significantly reduced visceral fat in a dose-dependent manner, inhibited hypertrophy of adipocytes, improved carbohydrate metabolism, and reduced oxidative stress. These effects were seen in mice fed soybeans before fermentation, but were stronger in mice fed Natto. Therefore, soybean intake has beneficial effects and fermentation of soybeans enhances these effects. Natto was found to suppress fatty acid synthesis and promote fatty acid catabolism in the liver. These effects were also stronger with Natto compared with soybeans before fermentation. In addition, Natto had more potent beneficial effects on gut microbiota compared to soybeans. CONCLUSIONS: These results suggest that Natto intake supports maintenance of health.