Intestinal Microbiota of Older Japanese Females Adhering to a Traditional Japanese Brown Rice-Based Diet Pattern

<b>Background/Objectives</b>: Some Japanese people still adhere to a systematic traditional Japanese diet pattern (the Shokuyo diet) consisting mainly of brown rice, vegetables, legumes, and small amounts of fish. We investigated the impact of this dietary pattern on the intestinal microbiota of its female consumers. <b>Methods</b>: The intestinal microbiota of 19 Japanese females in their 60s and 70s consuming the Shokuyo diet (Shokuyo diet group) and 50 females of the same age consuming a normal Japanese diet (NJ diet group) were compared. The NJ diet group was further subdivided into a healthy NJ diet H subgroup, comprising females (<i>n</i> = 19) without any diseases, and an unhealthy NJ diet UH subgroup (<i>n</i> = 31) consisting of females with certain diseases, and a subgroup analysis was performed. Intestinal microbiota analysis was performed using 16S rRNA gene amplicon sequencing. <b>Results</b>: The β-diversity of the intestinal microbiota significantly differed between the Shokuyo diet and NJ diet groups. Similarly, in the subgroup analysis, β-diversity also significantly differed between the NJ diet UH subgroup and the Shokuyo diet group. However, no significant difference was observed between the NJ diet H and Shokuyo diet groups. These results indicate that the intestinal microbial composition of the Shokuyo diet group resembled that of the healthy participants, and that differences in intestinal microbial composition between the Shokuyo and NJ diet groups were strongly influenced by the presence of participants with diseases in the NJ diet group. That is, differences in β-diversity may have been strongly mediated by the health status of the participants. <b>Conclusions</b>: Consumption of the Shokuyo diet may be associated with a healthy intestinal microbial composition in older Japanese female, suggesting its potential as a viable dietary intervention option.