Joint Dietary and Gut Microbial Profiling and the Fatty Liver Index in Community-Dwelling Older Japanese: A Cross-Sectional, Hypothesis-Generating Analysis from the Kyotango Longevity Study.

BACKGROUND

Diet and the gut microbiota are each associated with hepatic steatosis, but their joint variation and shared explanatory contribution are rarely quantified in older Asian community-dwelling populations.

METHODS

In 701 non-heavy-drinking Kyotango longevity cohort adults, habitual diet (BDHQ; 31 food groups) and stool 16S rRNA microbiome (47 genera; CLR-transformed) were related to the fatty liver index (FLI) by canonical correlation analysis (CCA), reduced-rank regression (RRR), and bootstrap mediation; FIB-4 was a secondary exploratory outcome.

RESULTS

Four dietary patterns and four microbial clusters emerged. CCA revealed multivariate diet-microbiota co-variation (four significant canonical correlations; r = 0.40-0.46; all p < 0.05). Combined RRR (n = 697 with complete FLI data) explained 11.1% of FLI variance in-sample (permutation p = 0.006), although cross-validated R2 was negative, reframing the model as hypothesis-generating rather than predictive. Bootstrap mediation suggested that 12.6% of the diet-on-FLI effect was carried by the microbiota (95% bootstrap CI excluding zero). Of 1457 FDR-corrected food-genus pairs, one was significant (fruits × Eubacterium eligens; r = +0.202, q = 1.0 × 10-4).

CONCLUSIONS

In this cross-sectional, hypothesis-generating analysis with no individual-level predictive utility, dietary patterns and gut microbial composition co-vary and jointly relate to FLI. The findings describe population-level covariance patterns for future prospective diet-microbiome intervention testing; external validation in independent cohorts is essential.