indigestible

Indigestible refers to materials that are not digested by the human gastrointestinal tract or absorbed as nutrients. In nutrition, indigestible components pass through the small intestine largely intact and contribute little to metabolizable energy.

Common indigestible dietary components include cellulose, hemicellulose, and lignin from plant cell walls, resistant starch, and certain nondigestible oligosaccharides. These substances resist human digestive enzymes and pass into the colon where some are fermented by gut microbes.

Indigestible matter adds bulk to stool, helps regulate bowel movements, and undergoes microbial fermentation to short-chain fatty acids in the colon. These fatty acids can serve as an energy source for colonocytes and may influence gut health and metabolism.

Because they are not absorbed, indigestible components contribute little to caloric intake, and energy accounting from foods typically subtracts their fecal energy. Dietary guidance often emphasizes adequate intake of indigestible fiber to support digestion and health.

The term is also used in medical contexts to describe swallowed items that cannot be digested, such as certain nonfood objects, which may require medical evaluation if they cause obstruction. In food science, indigestible does not imply harm; many indigestible ingredients influence texture, satiety, and nutrient dynamics.