Non-digestible oligosaccharides (NDOs) are short-chain (degree of polymerization 3–10) water-soluble carbohydrates, primarily including galacto-oligosaccharides (GOS), fructo-oligosaccharides (FOS), and mannooligosaccharides, which escape enzymatic digestion in the upper gut and are fermented by select saccharolytic microbes in the colon. In vitro and animal studies show that NDO fermentation elevates luminal short-chain fatty acid (SCFA) concentrations.
These processes—namely, increased fermentation products (SCFAs, and lactic acid) and osmotic load—are expected to increase fecal water content and bulk, resulting in higher stool frequency and softer consistency.
Placebo-controlled studies in adults with functional constipation show that GOS 5–11 g day−1 or inulin-type FOS 10 g day−1 can raise stool frequency by approximately one bowel movement per week and shift stool consistency towards Bristol Scale types 3–4.