Galacto-oligosaccharide (GOS) is a prebiotic fiber composed of shorter chains of galactose molecules, ending with a glucose molecule. Like other prebiotic fibers such as inulin and oligofructose, GOS resists digestion by human enzymes as it passes through the stomach and small intestine. Once in the large intestine, it is fermented by beneficial bacteria, such as bifidobacteria, promoting their growth and contributing to different health benefits.  

Certain types of GOS can be found in very limited amounts in some plants. Commercially used GOS is produced from lactose, the sugar found in cow’s milk, by adding galactose units. 

GOS is mostly known for its use in infant formula but also certain dairy products and supplements to support digestive health and enhance the immune function. In many formulations, GOS is combined with fructo-oligosaccharides (FOS) to mimic the benefits of human milk oligosaccharides (HMO) and further support a balanced gut microbiota in both infants and adults.