Grain, Gluten, and Dietary Fiber Intake Influence Gut Microbial Diversity: Data from the Food and Microbiome Longitudinal Investigation.

Although short-term feeding studies demonstrated effects of grains, fiber, and gluten on gut microbiome composition, the impact of habitual intake of these dietary factors is poorly understood. We examined whether habitual intakes of whole and refined grains, fiber, and gluten are associated with gut microbiota in a cross-sectional study. This study included 779 participants from the multi-ethnic Food and Microbiome Longitudinal Investigation study. Bacterial 16SV4 rRNA gene from baseline stool was amplified and sequenced using Illumina MiSeq. Read clustering and taxonomic assignment was performed using QIIME2. Usual dietary intake was assessed by a 137-item food frequency questionnaire. Association of diet with gut microbiota was assessed with respect to overall composition and specific taxon abundances. Whole grain intake was associated with overall composition, as measured by the Jensen-Shannon divergence (multivariable-adjusted P trend for quartiles = 0.03). The highest intake quartile was associated with higher abundance of Bacteroides plebeius, Faecalibacterium prausnitzii, Blautia producta, and Erysipelotrichaceae and lower abundance of Bacteroides uniformis. These bacteria also varied by dietary fiber intake. Higher refined grain and gluten intake was associated with lower Shannon diversity (P trend < 0.05). These findings suggest that whole grain and dietary fiber are associated with overall gut microbiome structure, largely fiber-fermenting microbiota. Higher refined grain and gluten intakes may be associated with lower microbial diversity. Significance: Regular consumption of whole grains and dietary fiber was associated with greater abundance of gut bacteria that may lower risk of colorectal cancer. Further research on the association of refined grains and gluten with gut microbial composition is needed to understand their roles in health and disease.

US nativity and dietary acculturation impact the gut microbiome in a diverse US population.

Little is known regarding the impact of immigrant acculturation on the gut microbiome. We characterized differences in the gut microbiome between racially/ethnically diverse US immigrant and US-born groups, and determined the impact of dietary acculturation on the microbiome. Stool samples were collected from 863 US residents, including US-born (315 White, 93 Black, 40 Hispanic) and foreign-born (105 Hispanic, 264 Korean) groups. We determined dietary acculturation from dissimilarities based on food frequency questionnaires, and used 16S rRNA gene sequencing to characterize the microbiome. Gut microbiome composition differed across study groups, with the largest difference between foreign-born Koreans and US-born Whites, and significant differences also observed between foreign-born and US-born Hispanics. Differences in sub-operational taxonomic unit (s-OTU) abundance between foreign-born and US-born groups tended to be distinct from differences between US-born groups. Bacteroides plebeius, a seaweed-degrading bacterium, was strongly enriched in foreign-born Koreans, while Prevotella copri and Bifidobacterium adolescentis were strongly enriched in foreign-born Koreans and Hispanics, compared with US-born Whites. Dietary acculturation in foreign-born participants was associated with specific s-OTUs, resembling abundance in US-born Whites; e.g., a Bacteroides plebeius s-OTU was depleted in highly diet-acculturated Koreans. In summary, we observed that US nativity is a determinant of the gut microbiome in a US resident population. Dietary acculturation may result in loss of native species in immigrants, though further research is necessary to explore whether acculturation-related microbiome alterations have consequences for immigrant health.