Fructans

Fructans are carbohydrates built mainly from linked fructose units. The name describes a family of molecules rather than a single substance: their chains can differ in length and structure. Inulin and the shorter fructooligosaccharides, often abbreviated FOS, belong to the inulin-type fructans. Although fructose is their main building block, these linked chains have different digestive properties from individual fructose molecules .^1,2

Human digestive enzymes do not readily break down inulin-type fructans in the small intestine. They therefore become available to microorganisms farther along the digestive tract, which can ferment them. This helps explain their classification as nondigestible carbohydrates and their use as dietary fibers. Shorter chains generally ferment more rapidly than longer ones, so the broad label “fructans” does not imply identical behavior for every preparation .^1,2

Fermentability also explains why consuming inulin-type fructans can increase gas or bloating. Whether these effects become noticeable depends partly on the amount consumed and the particular fructan preparation. Inulin-type fructans are also studied as prebiotics, substances selectively used by gut microorganisms in ways that benefit the host. Their prebiotic potential and their digestive tolerability are separate features .^1,2