Fructooligosaccharides (FOS), also known as oligofructose or oligofructan, are found naturally in many vegetables including bananas, onions, chicory root, garlic, asparagus, barley, wheat, jícama, and tomatoes. The Jerusalem artichoke and its relative, yacón have been found to have the highest concentrations of FOS of cultured plants.
The name comes from "oligo" meaning few, and saccharide meaning sugar. Therefore, FOS consists of short chains of fructose molecules. However, unlike fructose, which is rapidly digested and absorbed, fructooligosaccharides resist hydrolysis by salivary and intestinal digestive enzymes.
FOS helps to improve gastrointestinal health by serving as a substrate for microflora (healthy bacteria) in the large intestine. For the same reason, it has also been touted as a supplement for preventing yeast infections.
Several studies have found that FOS (like inulin) promotes calcium absorption. This is becasue the healthy bacteria in the lower gut ferment FOS, helping to reduce pH. Calcium is more soluble in acid and therefore more of it comes out of food and is available to move from the gut into the bloodstream.
FOS provides fiber, digestive benefits and calorie sweetness to a variety of new Functional Foods.
Hartemink, R.: Prebiotic effects of Non-digestible oligo- and polysaccharides. PhD thesis, Wageningen University, the Netherlands, 1999, 218 p. ISBN 90-5808-051-X.