Association of dietary fiber intake and gut microbiota in healthy adults.

1569 Background: Increasing evidence has shown that gut microbiota alterations may play a role in colorectal cancer risk. Diet, particularly fiber intake, may modify gut microbiota composition, which may consequently impact cancer risk development. We investigated the relationship between dietary fiber intake and gut microbiota in healthy humans. Methods: Using 16S rRNA gene sequencing, we assessed gut microbiota in fecal samples from 151 healthy adults in two independent study populations: Study A, n = 75 (healthy controls from a colorectal cancer case-control study), and Study B, n = 76 (polyp-free subjects from a cross-sectional colonoscopy study). We calculated energy-adjusted total dietary fiber intake of participants based on food frequency questionnaires. For each study population, we evaluated the relationship between quartiles of higher fiber intake as a continuous ordinal variable, and global gut microbiota community composition (via PERMANOVA of weighted UniFrac distance) and specific taxon abundance (via DESeq2). Results: We found that fiber intake was significantly associated with overall microbial community composition in Study B (p = 0.003) but not Study A (p = 0.68), after adjustment for age, sex, race, body mass index, and cigarette smoking. In a taxonomy-based meta-analysis of these two study populations, higher fiber intake was associated with lower abundance of genus Actinomyces (fold change [FC] = 0.769, p = 0.003), and higher abundance of genera Faecalibacterium (FC = 1.153, p = 0.03), Lachnospira (FC = 1.167, p = 0.04), and SMB53 (FC = 1.201, p = 0.05). A species-level meta-analysis showed an association between higher fiber intake and higher abundance of Faecalibacterium prausnitzii (FC = 1.165, p = 0.03) and lower abundance of Ruminococcus bromii (FC = 0.828, p = 0.08). Conclusions: Our results suggest that higher intake of dietary fiber may alter gut microbiota in healthy adults. Given the potentially modifiable nature of the gut microbiota through diet, these findings warrant further study of diet-microbiota based colorectal cancer prevention strategies.