Galactan (galacto-oligosaccharide) intolerance

Galactans, raffinose, stachyose & other galactooligosaccharides

Galactan (galacto-oligosaccharide) intolerance


Galactooligosaccharides (GOS) are a wide range of chains of galactose (a sugar) molecules that are found in plants, including seaweeds, animals, microbes and fungi. Common food sources are legumes, such as beans, lentils, and seaweed-derived products.
See Galactooligosaccharides food table for listing of food containing GOS

Some GOS (α-linked galactosyl sucrose derivates) form part of the spectrum of fermentable sugars associated with intolerances (sometimes described as FODMAPs), whereas a different class of GOS have been shown to have multiple beneficial properties as prebiotics (β-linked lactose-derived).


Galacto-oligosaccharides are inadequately broken down by digestion in humans, but are metabolized by gut bacteria. The fermentation produces large amounts of gas, often resulting in bloating, flatulence and abdominal pain or cramps. GOS are widely and increasingly added to manufactured food because of their beneficial prebiotic (promoting the growth of beneficial intestinal microorganisms) effects. These include increased intestinal calcium absorption, anti-inflammatory action and promotion of beneficial gut bacteria. Individuals with GOS intolerance are often also intolerant to fructo-oligosaccharides (FOS).

Frequency in population and natural history

The frequency of significant symptoms after GOS ingestion is unknown, but appears widespread. As humans poorly digest GOS, everyone will develop symptoms with high enough doses.


Bloating, fullness, flatulence, abdominal pain or cramps, increased intestinal sounds, nausea and changes in stool consistency (diarrhea, constipation or both) are most common.

The symptoms resemble those of functional disorders or Irritable Bowel Syndrome (IBS).

Symptoms may appear several hours after meals and last for over 24 hours.

Testing and diagnosis

A dietary history can generally identify an intolerance to GOS, as the related foods are easily identified (see food list). No breath test or other form of testing is currently validated.


Reduction of the intake of galactans to individually tolerated levels will lead to symptom relief in most individuals within a few days.

Often other intolerances to other classes of poorly absorbed carbohydrates (FODMAP’s), especially fructans (see fructans) co-exist, necessitating further diagnostics and dietary adaptations.

See Food tables for a listing of GOS food content

GOS are not sweet.