New high-specificity fibers with strong and consistent responses across individuals.

Individual variability in gut microbiota responses limits the consistency of health benefits from prebiotic fiber interventions. Building on our concept of fiber hierarchical specificity, defined as the selective alignment and use of fibers by a narrow subset of gut microbes, we evaluated new putative high-specificity fibers for their ability to promote predictable and intense microbial shifts across individuals. Here, six candidate fibers (Acacia gum, Fucogalactan, Gellan gum, Guar gum, Locust bean gum, and Xylooligosaccharides) were tested in vitro using fecal microbiota from ten donors and compared to low-specificity (Fructooligosaccharides) and high-specificity (an insoluble glucan) reference fibers. SCFA analysis showed that Fucogalactan and Guar were strongly propiogenic, while Acacia and Locust promoted balanced SCFA production. Gellan exhibited minimal fermentability. Acacia, Fucogalactan, Guar, and Locust consistently enriched putative beneficial genera (Eisenbergiella, Hungatella, Anaerotruncus, and Parabacteroides, respectively), with strong and consistent responses across individuals, features characteristic of high-specificity fibers. In contrast, Fructooligosaccharides and Xylooligosaccharides produced more variable, and less intense responses. Our findings support Acacia, Fucogalactan, Guar, and Locust as high-specificity fibers that induce consistent, taxon-targeted shifts in the gut microbiome. These expand the repertoire of high-specificity fibers-a promising prebiotic approach for predictable microbiota modulation and related health outcomes.