The term oligosaccharide refers to a short chain of sugar molecules fructo oligosaccharides fos and inulin which are found in many vegetables consist of short chains of fructose molecules galacto oligosaccharides gos which also occur naturally consist of short chains of galactose molecules these compounds can be only partially digested by humans when oligosaccharides are consumed the undigested portion serves as food for friendly bacteria such as bifidobacteria and lactobacillus