Fructo-Oligosaccharides (FOS) are short-chain, soluble fibers that act as a prebiotic. They resist digestion in the small intestine and travel to the colon, where they feed beneficial bacteria. Compared to longer-chain inulin fibers, this form tends to have a milder flavor and a lower chance of causing gas or bloating.
People use FOS to encourage regularity and nourish their gut microbiome. You can find it added to foods or take it as a powder stirred into water or smoothies. Many people begin with small servings to let the digestive system adapt.