Xylo-oligosaccharides (XOS) are polymers of the sugar xylose. XOS is produced from the xylan fraction in plant fiber. Their C5 structure is fundamentally different from other prebiotics, which are based upon C6 sugars. Xylo-oligosaccharides have been commercially available since the 1980s. Xylo-oligosaccharides act as a prebiotic, selectively feeding beneficial bacteria such as bifidobacteria and lactobacilli within the digestive tract. A large number of clinical trials have been conducted with XOS, demonstrating a variety of health benefits, including improvements in blood sugars and lipids, digestive health benefits, laxation, and beneficial changes to immune markers.