Relationship between the Japanese-style diet, gut microbiota, and dementia: a cross-sectional study

Abstract Objective Previous studies have shown associations between the gut microbiota, microbial metabolites, and cognitive decline. However, the effect of the dietary composition on such associations has not been fully investigated. Methods We performed a cross-sectional sub-analysis of data from our prospective hospital-based cohort study. We assessed their demographics, dietary composition, risk factors, cognitive function, brain imaging, gut microbiome, and microbial metabolites. On the basis of previous studies, a nine-component traditional Japanese diet index (JDI9), a 12-component modern JDI (JDI12), and a 12-component revised JDI (rJDI12), were defined. We evaluated the relationships between the JDI scores, cognitive function, and the gut microbiome and microbial metabolites using multivariable logistic regression analyses. Results We analyzed data from 85 eligible participants (61% women; mean age: 74.6±7.4 years). Compared with participants with dementia, those without dementia were more likely to consume foods in the JDI12, including fish and shellfish (64.5% vs. 39.1%, P=0.048), mushrooms (61.3% vs. 30.4%, P=0.015), soybeans and soybean-derived foods (62.9% vs. 30.4%, P=0.013), and coffee (71.0% vs. 43.5%, P=0.024). There were non-significant trends towards lower fecal concentrations of gut microbial metabolites in participants with a more traditional Japanese diet. Participants with dementia had lower JDI scores than participants without dementia (dementia vs. non-dementia, median JDI9 score: 5 vs. 7, P=0.049; JDI12: 7 vs. 8, P=0.017; and rJDI12: 7 vs. 9, P=0.006, respectively). Conclusions Adherence to a traditional Japanese diet was found to be inversely associated with cognitive decline and tended to be associated with lower concentrations of gut microbial metabolites.