A prebiotic-postbiotic combination supports dietary carbohydrate-targeting functional properties in a fiber-deprived microbiota

Dietary fiber deprivation compromises gut mucosal barrier integrity by promoting microbial degradation of host mucus, a process linked to various gut-related auto immune diseases. While postbiotics are considered safer alternatives to fiber for susceptible patients, their mechanistic ef- fects on a fiber-deprived gut remain poorly understood. Here, we demonstrate in a mouse model that a fermented postbiotic, alone or in combination with a prebiotic and aloe vera, counteracted the increase of detrimental properties of the microbiota on a fiber-free diet. The supplement regimen reshaped the gut microbiota, counteracting the expansion of key mucin-degrading bac- teria, including Akkermansia muciniphila and Parabacteroides goldsteinii . Metatranscriptomic analysis revealed this compositional change corresponded to a community-wide functional pivot away from expressing mucinolytic enzymes, such as sialidases, and towards utilizing alternative substrates. These microbial shifts recapitulated the effects of dietary fiber reintroduction and translated to direct host benefits, including sustentation of the colonic mucus layer and attenu- ation of diet-induced type III immune cytokine expression. Our findings provide a mechanistic rationale for using postbiotics to functionally replace dietary fiber, offering a promising strategy to support gut homeostasis in contexts where fiber intake is limited.