Effects of a Defatted Rice Bran–Inulin Combination on Gut Bifidobacteria, Butyrate Levels, and Exploratory Behavior in Middle-Aged Female Mice

Abstract

Middle-aged females are particularly susceptible to age-related gut dysbiosis and immunosenescence, largely driven by hormonal shifts. Dietary fiber, a crucial modulator of gut microbiota, represents a promising strategy to promote healthy aging in this population. This study investigated the effects of defatted rice bran (RB), inulin (INU), and the combination of RB and INU (RBI) on age-related alterations in a natural aging mouse model. Middle-aged female mice were assigned to four dietary groups: standard diet (Ctrl), INU, RB, and RBI, along with a young control group (You). After a 3-month intervention, compared with the Ctrl group, RBI supplementation increased fecal butyrate levels and Bifidobacterium abundance and exhibited potential to improve exploratory behavior. A trend toward higher proportions of circulating CD4+ Naïve and CD8+ Naïve T cell populations (p = 0.06) was also observed. Although both RB and RBI increased the abundance of bifidobacteria, the effect was more pronounced with the RBI diet. These findings suggest that defatted RB, particularly when combined with INU, may support gut microbiota composition, exploratory behavior, and immune function during aging, though further mechanistic and larger-scale studies are warranted.