Diachronic analysis of food culture and butyrate production potential in the Kyotango region, Japan: from the Jomon period to the present

Kyotango City, Kyoto Prefecture, has roughly three times the national centenarian rate and a gut microbiota notably enriched in butyrate-producing bacteria ( Roseburia spp., Faecalibacterium spp., and relatives). Yet the historical and cultural origins of this distinctive microbiome have not been examined systematically. Using a large language model (LLM) as the literature-integration tool, we conducted a narrative integrative review that synthesizes food culture evidence from six temporal cross sections spanning the Jomon period to the present. Drawing on primary archaeological data (Hamazume shell midden), the Engishiki legal codes, the Kebukigusa food chronicle, early modern regional cuisine surveys, and contemporary cohort studies, we cross-referenced dietary ingredients from each era against known substrates of butyrate-producing bacteria. Diverse seafood and dietary fiber sources recur in all six eras, and preserved and fermented foods are added and intensified over time, culminating in heshiko, a year-long rice bran fermentation of mackerel. We summarized each era with the Butyrate Production Potential Score (BPPS), a four-axis index scored with an explicit rubric by four independent raters (one human and three open-weight LLMs); the pooled scores showed excellent inter-rater reliability (ICC(2, k ) = 0.91), and the main pattern was robust to alternative axis weights. One particularly striking finding is the 1100-year continuity of Zanthoxylum piperitum (sansho): first recorded in the Engishiki (927 CE) as a Tango Province tribute item, it remains an essential ingredient in modern heshiko fermentation. We propose that the butyrate-producing bacteria-dominant gut environment of Kyotango residents may reflect a food culture structure dating back to the Jomon period, while acknowledging that causal verification awaits future empirical work.