Fructo-Oligosaccharides, or FOS, are short-chain sugars that work as a prebiotic fiber. Your body does not digest them in the stomach or small intestine. Instead, they travel intact to the colon where friendly bacteria ferment them for fuel.
People use FOS powder or capsules to encourage regularity and a healthy gut microbiome. Many stir a small scoop into water, smoothies, or food. Supporting gut health this way can also have a knock-on effect on immune function.
Start low and increase the dose slowly. That approach gives your digestive system time to adapt and helps you avoid gas, bloating, and stomach cramps. Anyone with IBS or a known FODMAP sensitivity should be cautious, as this fiber ferments quickly and can trigger discomfort.