Galactooligosaccharides (GOS) are a group of carbohydrates made up of a chain of galactose units. They are made from lactose and are similar in structure to carbohydrates found naturally in human breast milk. Their unique chemical structure enables them to escape digestion both in the stomach and the intestines, allowing them to pass undigested into the large intestine, where they act as prebiotics, stimulating the growth and activity of beneficial bacteria.