Galactooligosaccharides (GOS) are short chains of variable length made up of the sugars galactose and glucose. While GOS are poorly digested by human enzymes, there are gut bacteria that are able to break down GOS. GOS thus serve as an energy source for beneficial bacteria that live in the human intestine. GOS are considered prebiotics, which are defined as food compounds that are indigestible by humans but are digestible by intestinal bacteria. Other indigestible oligosaccharides with prebiotic effects include fiber gums, fructooligosaccharides (FOS), inulins, isomalto-oligosaccharides, lactilol, lactosucrose, lactulose, pyrodextrins, soy oligosaccharides, and xylooligosaccharides.
Prebiotics differ from probiotics. Probiotics are bacteria (such as Lactobacillus and Bifidobacterium) often taken as supplements to promote the establishment of beneficial gut bacteria.
GOS have numerous purported beneficial effects. GOS are believed to mimic the oligosaccharides found naturally in human breast milk and may contribute to the known health benefits of breastfeeding. Infant formulas in Europe have been supplemented with GOS since 2001, and numerous studies support the safety and prebiotic effects of GOS supplementation in infants.
Results of other studies suggest that GOS may have beneficial effects for the immune system, in treating constipation, in preventing atopic dermatitis, and in maintaining bone density. Although there is preliminary evidence supporting these potential benefits, more studies are needed.

Related Terms

Beta-galactosidase, beta-galactosidase, Bi2muno®, Bi2muno®, Bi2tos®, Bi2tos®, bifidogenic, Bimuno®, Bitos®, Elix'or®, galacto-oligosaccharide, galactosyl lactose, oligogalactose, oligogalactosyl lactose, prebiotic, probiotic, synbiotic, transgalacto-oligosaccharides (TOS), transgalactooligosaccharides, Vivinal®GOS.
Note: The galactooligosaccharides designed for human use are marketed by Clasado, Inc. (UK) under the brand name Bi2muno®, while Bi2tos® is designed for animal use.

evidence table

These uses have been tested in humans or animals. Safety and effectiveness have not always been proven. Some of these conditions are potentially serious, and should be evaluated by a qualified healthcare provider.
Allergic disorders (Grade: C)
Limited research indicates that infants receiving probiotics and GOS supplements may have a reduced incidence of atopic eczema. Additional research is needed.
Atopic dermatitis (Grade: C)
Preliminary research indicates that infants receiving either prebiotics or a combination of probiotics and prebiotics may have a reduced incidence of atopic eczema. Further research is required to determine the effects of GOS alone.
Bone loss (Grade: C)
Limited research in postmenopausal women suggests that GOS supplementation may increase calcium absorption. Additional research is needed before firm conclusions can be drawn.
Colic (Grade: C)
Limited research has been completed on the effect of prebiotic supplementation on reducing colic in infants. While these preliminary results are encouraging, more well-designed and well-controlled studies are needed.
Constipation (Grade: C)
Results of preliminary research assessing the effect of prebiotics on constipation are conflicting. More well-designed trials are needed to determine the safety and effectiveness of GOS for constipation relief.
Growth (infant growth and development) (Grade: C)
In preliminary research, infants fed formula supplemented with a combination of prebiotics had similar amounts of growth compared with infants fed unsupplemented formula. Additional research is needed.
Immunomodulation (Grade: C)
Some preliminary evidence indicates that prebiotic supplementation may benefit immunity in newborn infants. More high-quality research is needed before a conclusion can be drawn.
Lipid lowering effects (Grade: C)
Limited research has shown a lack of effect of a mixture of prebiotics on blood lipid levels in healthy volunteers. Further research is needed to determine the effect of prebiotics such as GOS on blood lipids in other populations, such as those with elevated levels of blood lipids.