(P27-10-26) Higher Dietary Vitamin B12 Linked to Lower Fecal Short-Chain Fatty Acids and Changes in Gut Microbial Function in Healthy United States Adults

Objectives: Vitamin B₁₂ is acquired through consumption of animal-source foods and supplements. Often correlated with dietary B₁₂ is methionine, which is associated with lower health-promoting fecal short chain fatty acid (SCFA) concentrations in animal and culture models. The effect of dietary B₁₂ on the gut microbiota and its association with fecal SCFAs in healthy humans is unknown. This study determined relationships between dietary B₁₂ and the human gut microbiome from healthy U.S. adults in an observational cohort.

Methods: Habitual diet and fecal shotgun metagenomes were integrated alongside measurements of plasma B₁₂ and fecal SCFAs from healthy U.S. adults that completed an observational, cross-sectional study balanced for age, sex, and BMI (n=247). Plasma B₁₂ was quantified using a competitive chemiluminescent enzyme immunoassay. Diet was assessed using the Block 2014 Food Frequency Questionnaire. Fecal SCFAs were measured using gas chromatography. The gut microbiome was profiled using shotgun metagenomics. Differentially abundant taxa were identified based on dietary B₁₂ intake. Gut microbial metabolic pathways were quantified from quality-filtered merged reads and metagenome-assembled genomes. Associations between diet and fecal SCFAs were examined using generalized linear models adjusting for age, sex, BMI, dietary methionine, and fiber intake. Associations between diet, fecal SCFAs, and the gut microbiome were examined using Random Forest regressions.

Results: Participants consumed adequate B₁₂ and had replete plasma B₁₂ concentrations. Stratification into dietary groups based on B₁₂ intake from foods and supplements revealed higher intake from either source was associated with a reduction in gut microbes capable of anaerobic B₁₂ biosynthesis, while higher intake from both sources was associated with lower fecal SCFA concentrations after controlling for fiber and methionine intake. Differences in microbial taxa between dietary groups were limited, but machine learning models revealed consistent positive associations between abundances of methionine biosynthesis and inositol degradation pathways and fecal propionate concentrations in groups with lower B₁₂ intake.

Conclusions: Our results indicate that excessive dietary B₁₂ may perturb the gut microbiome, lowering fecal SCFA production.

Funding Sources: USDA-ARS