Mannanoligosaccharides (MOS) are prebiotic fibers derived primarily from the cell walls of yeast (Saccharomyces cerevisiae) and are commonly used in animal nutrition and, to a lesser extent, in human supplements. Their primary mechanism of action is the modulation of gut microbiota and the enhancement of gut barrier function, which directly relates to the health of the small intestine.

Scientific studies, particularly in animal models (such as poultry and swine), have shown that MOS supplementation can reduce the colonization of pathogenic bacteria in the small intestine by acting as decoy binding sites, thereby preventing pathogens like Salmonella and E. coli from adhering to the gut lining. Additionally, MOS can promote the growth of beneficial bacteria, such as Lactobacilli and Bifidobacteria, which support gut health and immune function.

In humans, the evidence is more limited, but some studies suggest that MOS may have similar effects on gut microbiota composition and could support small intestinal health, especially in the context of supporting normal immune function and maintaining the integrity of the gut barrier. However, clinical trials in humans are fewer and often limited by small sample sizes or short durations.

Overall, there is a moderate level of scientific evidence supporting the use of mannanoligosaccharides for supporting small intestinal health, particularly in animal studies, with emerging but still limited data in humans.