Microbiota-Dependent Fiber Responses: A Proof-of-Concept Study on Short-chain Fatty Acid Production in Prevotella- and Bacteroides-Dominated Healthy Individuals.

Background: Dietary fiber supports metabolic health via microbial fermentation, producing short-chain fatty acids (SCFAs). However, metabolic responses to fiber vary between individuals, potentially due to differences in gut microbiota composition. The Prevotella-to-Bacteroides (P/B) ratio has emerged as a potential biomarker for fiber responsiveness.

Objective: This study examined how stratified fiber supplementation affects microbial and metabolic outcomes in individuals with Prevotella- or Bacteroides-dominated microbiota.

Methods: In this single-blinded, randomized cross-over study, 23 healthy adults were classified as P-type (≥10% Prevotella) or B-type (≥10% Bacteroides) via 16S rRNA sequencing. Participants consumed 15 g/day of arabinoxylan (AX), inulin (INU), or placebo (PLA) for one week each, with 2-week washouts. After each phase, fasting and postprandial plasma SCFAs, branched-chain fatty acids (BCFAs), breath hydrogen, glucose, insulin, PYY, cholesterol, appetite ratings, and fecal microbiota were assessed. Data were analyzed using repeated measures ANOVA, Friedman test, and multivariate microbiome analysis.

Results: In P-types, AX increased fasting propionate vs. PLA (p = 0.04). In B-types, AX increased fasting propionate vs. INU (p = 0.02) and tended to elevate postprandial propionate vs. PLA in the first 60 minutes after breakfast (p = 0.05). AX also increased postprandial acetate vs. PLA in B-types (p = 0.04). INU reduced fasting BCFAs in B-types (p < 0.05) but did not increase SCFAs. Breath hydrogen varied widely in B-types after INU but not in P-types. Neither fiber affected glucose, insulin, or PYY. AX reduced appetite ratings in P-types (p < 0.05). INU increased Anaerostipes and Bifidobacterium and reduced Phocaeicola in both groups (q < 0.25). AX increased Fusicatenibacter in B-types (q = 0.18) and Paraprevotella in P-types (q = 0.17).

Conclusions: B-types exhibited fiber-specific shifts in SCFA and BCFA metabolism and breath hydrogen, whereas P-types displayed a more limited overall response, with fewer metabolic and microbial parameter affected. These findings highlight the complexity of diet-microbiota interactions and support the potential relevance for microbiota-based nutrition strategies. German Register of Clinical Studies (DRKS00028898).