What are Fructans and Galacto-oligosaccharides?

Fructans are fructose polymers and are the naturally occurring storage carbohydrates of a variety of vegetables, including onions and garlic, fruits and cereals.  Additional sources of fructans are inulin or Fructo-oligosaccharides (FOS).  Inulin and FOS are increasingly being added to foods for their known prebiotic effects. The human small intestine does not produce enzymes capable of hydrolysing these fructose-fructose bonds and as such fructans cannot be absorbed across the small intestine.  They are then delivered into the large bowel, where they can be readily fermented by colonic bacteria.  Fructans alone can induce abdominal symptoms and can also exaggerate those associated with fructose malabsorption or lactose intolerance.  Hence, fructans are often limited in any dietary modification for patients with fructose malabsorption and IBS.

Like fructans, galacto-oligosaccharides or chains of galactose molecules are also malabsorbed in the small intestine.  Individuals do not produce enzymes that hydrolyse galactose-galactose bonds and they too are readily fermented by bacteria in the large bowel.  Significant dietary sources of galactans (raffinose and stacchyose) include legumes such as lentils, chickpeas and red kidney beans.

Vegetarians often consume large amounts of galactans due to increased consumption of legumes as they often provide an important source of protein in a vegetarian diet.