What are galacto-oligosaccharides (GOS)?
Galacto-oligosaccharides (galacto from galactose; oligo = few; saccharide = sugar) or GOS are composed of galactose molecules with one glucose on the end, altogether containing 3-8 simple sugars. GOS cannot be digested in the human small intestine, so it travels unchanged into the large intestine, where beneficial colonic bacteria break them down into gases and short-chain fatty acids (SCFAs), which can be absorbed and used by the body .
Galacto-oligosaccharides are similar to human milk oligosaccharides (HMO) .
Semi-synthetic GOS can be produced from lactose . GOS (up to about 5 g/100 g) can be added as a soluble fiber to infant formula, powdered milk, biscuits, dairy products, fruit drinks, confectionery, cereal bars or other commercial foods.
GOS may be included in some prebiotic and soluble fiber supplements.
Possible GOS Benefits
- GOS promote the growth of beneficial Bifidobacteria in the large intestine  but are, according to Journal of Nutrition, currently not considered prebiotics .
- GOS act as a soluble dietary fiber, which may soften the stool and increase the frequency of bowel movements .
GOS Safety and Side Effects
GOS is currently not yet Generally Recognized As Safe by the US Food and Drug Administration (FDA) .
GOS in amounts 12 g per day or lower is usually well tolerated. Larger amounts may cause abdominal bloating, excessive gas (flatulence) or other mild gastrointestinal symptoms .