INS and diabetes mellitus: As we had observed significant associations between fruit-intake frequency and gut microbial vitamin B1 and B2 pathways, and gut microbial vitamin B1 and B2 pathways are associated with glucose-related health factors (insulin level, glucose level, HOMA-IR, and diabetes), we performed bidirectional mediation analysis between fruit-intake frequency, gut microbial vitamin B1 and B2 pathways, and glucose-related health factors.