MOS (mannan-oligosaccharides)

MOS, or mannan-oligosaccharides, are compounds derived from the yeast cell wall whose main sugar is mannose. Although they are usually grouped with [prebiotics](/glossary/prebiotics), their primary mechanism is quite different from that of [FOS](/glossary/fos-fructo-oligosaccharides): MOS do not mainly feed beneficial bacteria. Their clever trick is to act as a decoy. Many undesirable gut microbes carry surface structures that recognise mannose, which they normally use to latch onto the intestinal wall and colonise it. When MOS are present, these bacteria bind to the mannose of the MOS instead, are swept along with the digesta and are carried out in the stool, so they never get a foothold in the gut. This anti-adhesion strategy is sometimes described as bacterial decoupling. MOS are also studied for supporting the gut's local immune response. They are used at a low inclusion rate in some foods, frequently paired with FOS so that two complementary mechanisms work side by side: FOS feeding the good bacteria, MOS removing the bad. On a label, MOS or yeast cell-wall extract may appear among the ingredients. Together with [inulin](/glossary/inulin) and FOS, MOS round out the prebiotic toolkit of premium digestive-care diets. See the [Petipedia glossary](/glossary).

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