Association of dietary fiber intake and gut microbiota in healthy adults

BACKGROUND: Increasing evidence has shown that gut microbiota may play a role in colorectal cancer. Diet, particularly fiber intake, may modify gut microbiota composition, which may consequently impact cancer risk. OBJECTIVE: We investigated the relationship between total dietary fiber intake and gut microbiota in healthy humans. DESIGN: Using 16S rRNA gene sequencing, we assessed gut microbiota in fecal samples from 151 healthy adults in two independent study populations: NCI, n= 75 (healthy controls from a colorectal cancer case-control study), and NYU, 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: Total fiber intake was significantly associated with overall microbial community composition in NYU (p=0.008) but not NCI (p=0.81), 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 higher abundance of select genera from class Clostridia: SMB53 (fold change [FC]=1.04, p=0.04), Lachnospira (FC=1.03, p=0.05), and Faecalibacterium (FC=1.03, p=0.06), and lower abundance of genera Actinomyces (FC=0.95, p=0.002), Odoribacter (FC=0.95, p=0.03), and Oscillospira (FC=0.96, p=0.06). A species-level meta-analysis showed a marginal association between higher fiber intake and higher abundance of Faecalibacterium prausnitzii (FC=1.03, p=0.07) and lower abundance of Eubacterium dolichum (FC=0.96, p=0.04) and Bacteroides uniformis (FC=0.97, p=0.05). CONCLUSIONS: Our results suggest that increased dietary fiber intake may impact gut microbiota composition in healthy adults, particularly in favor of putatively beneficial bacteria such as Faecalibacterium prausnitzii. Given the potentially modifiable nature of gut microbiota through diet, these findings warrant further study of diet-microbiota based colorectal cancer prevention strategies.