Abstract MP66: The Interplay Between Diet, Circulating Indolepropionate Concentrations, and Cardiometabolic Health in US Populations

Background: Indolepropionate (IPA), a tryptophan metabolite of human gut microbiota origin, is associated with lower risk of type 2 diabetes (T2D) in humans. The complex interplay among tryptophan intake, the gut microbiome, prebiotics, circulating IPA concentrations, and T2D risk has not been investigated. Objectives: We aimed to identify IPA-producing gut microbiota species and investigate potential diet-microbiota interaction on circulating IPA concentrations. Methods: We included 287 men from the Men’s Lifestyle Validation Study, a sub-study of the Health Professionals Follow-Up Study (HPFS), who provided up to two pairs of fecal samples and two blood samples approximately six months apart. Dietary intake was assessed using 7-day diet records. We identified microbial taxonomic features associated with plasma IPA concentrations using generalized linear regression and calculated a rank-based species score to reflect IPA-producing potential. Associations between plasma concentrations of tryptophan metabolites and T2D risk were examined in 13,032 participants from Nurses’ Health Study (NHS), NHSII, and HPFS. Results: Plasma IPA concentrations were associated with overall gut microbial profiles (permutational analysis of variance test, p=0.001). We identified 17 microbial species, such as Eubacterium eligens, Butyrivibrio crossotus , and Faecalibacterium prausnitzii , whose abundance was significantly associated with increased plasma IPA concentrations (false discovery rate < 0.05). A significant association between higher tryptophan intake and higher IPA concentrations was only observed among men who had higher fiber intake and a higher microbial species score consisting of the 17 species (p-interaction < 0.01). Similar modulation was also observed for major tryptophan food contributors including vegetables (p-interaction < 0.01), red/processed meat (p-interaction = 0.02), egg (p-interaction 0.01), dairy (p-interaction = 0.01), and whole grain (p-interaction < 0.01). Moreover, interactions persisted for all fiber subtypes (soluble/insoluble fiber and pectin). We documented 1,744 incident T2D cases during 218,603 person-years of follow-up. Plasma concentrations of tryptophan and three kynurenine-pathway metabolites (kynurenine, xanthurenate, and quinolinate) were positively associated with T2D risk while an inverse association was found for IPA. Conclusions: Specific microbial species and dietary fiber jointly modulate the associations between tryptophan intake and circulating IPA concentrations. In a subsequent analysis, IPA levels were predictive of lower T2D risk. Our findings suggest that the health effects of dietary tryptophan may depend on both gut microbiome composition and prebiotic consumption.