Fructo-oligosaccharides are linked by the β(2 → 1)-glycosidic bonds making the human digestive system unable to digest and metabolize the molecule. They reach the colon intact and are then hydrolyzed by the resident gut bacteria. Being undigested, they have been included in the list of dietary fibers. The current document https://www.tatanq.com/fos-improves-dietary-fiber-intake/