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 ratio has emerged as a potential biomarker for fiber responsiveness.

Objectives: This study examined how stratified fiber supplementation affects microbial and metabolic outcomes in individuals with Prevotella (P-type)- or Bacteroides-dominated (B-type) microbiota.

Methods: In this single-blinded, randomized crossover study, 23 healthy adults were classified as P-type (≥10% Prevotella) or B-type (≥10% Bacteroides) via 16S rRNA sequencing. Participants consumed 15 g/d of arabinoxylan (AX), inulin (INU), or placebo (PLA) for 1 wk each, with 2-wk washouts. After each phase, fasting and postprandial plasma SCFAs, branched-chain fatty acids (BCFAs), breath hydrogen, glucose, insulin, peptide YY, cholesterol, appetite ratings, and fecal microbiota were assessed. Data were analyzed using repeated-measures analysis of variance, the Friedman test, and multivariate microbiome analysis.

Results: In P-types, AX increased fasting propionate compared with PLA (P = 0.04). In B-types, AX increased fasting propionate compared with INU (P = 0.02) and tended to elevate postprandial propionate compared with PLA in the first 60 min after breakfast (P = 0.05). AX also increased postprandial acetate compared with 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 parameters affected. These findings highlight the complexity of diet-microbiota interactions and support the potential relevance for microbiota-based nutrition strategies. This trial (PERIFIB) was registered at the German Clinical Trials register (DRKS) as DRKS00028898.