Human milk oligosaccharides (HMOs), structurally similar to mucin glycans, enrich A. muciniphila and B. caccae while reducing M. gnavus.55,56 Specific HMOs (e.g., 2-fucosyllactose) increase cecal propionate, reduce colonic inflammation in IL10−/− mice, and modulate MD activity of M. gnavus.31 HMO supplementation also increases A. muciniphila abundance and short-chain fatty acid (SCFA) production in healthy mice57 and improves metabolic outcomes such as obesity through enhanced mucin secretion and glycosylation.58 Here, MUC5AC is linked to obesity due to melanocortin 4 receptor deficiency.