Fructooligosaccharide
Fructooligosaccharides (FOS) also sometimes called oligofructose or oligofructan, is a class of oligosaccharides used as an artificial or alternative sweetener. FOS use emerged in the 1980s in response to consumer demand for healthier and calorie-reduced foods.  The term oligosaccharide refers to a short chain of sugar molecules (in the case of FOS, fructose molecules).  Oligo means few, and saccharide means sugar.

# Chemistry
Two different classes of fructooligosaccharide (FOS) mixtures are produced commercially, based on inulin degradation or transfructosylation processes.
FOS can be produced by degradation of inulin, or polyfructose, a polymer of D-fructose residues linked by (2-1) bonds with a terminal (1-2) linked D-glucose. The degree of polymerization of inulin ranges from 10-60. Inulin can be degraded enzymatically or chemically to a mixture of oligosaccharides with the general structure Glu-(Fru)n  (GFn) and Frum, (Fm), with n,m ranging from 1 to 7. This process also occurs to some extent in nature, and these oligosaccharides can be found in a large number of plants, especially in Jerusalem artichoke and chicory. This type of FOS is mainly marketed commercially by Orafti Ltd., Tienen Belgium, which markets the product as Oligofructose (or Raftilose). Confusingly, the company also markets inulin as oligofructose. Other producers incluse the Dutch company Cosun (which markets the product as Frutafit or Frutalose) and others. The main components of this class are kestose (GF2), nystose (GF3), fructosylnystose (GF4), bifurcose (GF3), inulobiose (F2), inulotriose (F3) and inulotetraose (F4).
The second class of FOS is prepared by the transfructosylation action of a -fructosidase of Aspergillus niger on saccharose. The resulting mixture has the general formula of GFn with n ranging from 1 to 5. Contrary to the inulin derived FOS, the binding is not only (1-2), but other linkages do occur, though in limited numbers. This class is mainly produced in Japan by Meiji Seika Kaisha .
Because of the configuration of their osidic bonds, fructooligosaccharides resist hydrolysis by salivary and intestinal digestive enzymes. In the colon they are fermented by anaerobic bacteria. In other words, they have a lower caloric value, whilst contributing to the dietary fiber fraction of the diet.  Fructooligosaccharides are more soluble than inulins and are therefore sometimes used as an additive to yoghurt and other (dairy) products.  Fructooligosaccharides are used specially in combination with high-intensity artificial sweeteners, whose sweetness profile and aftertaste it improves.

# Food Sources
FOS is extracted from fruits and vegetables like bananas, onions, chicory root, garlic, asparagus, barley, wheat, jicama, and tomatoes, and leeks. The Jerusalem artichoke and its relative, yacon have been found to have the highest concentrations of FOS of cultured plants.

# Health Benefits
FOS has been a popular dietary supplement in Japan for many years, even before 1990, when the Japanese government installed a "Functionalized Food Study Committee" of 22 experts to start regulate "special nutrition foods or functional foods" which contained the categories of fortified foods (e.g., vitamin-fortified wheat flour), and is now becoming increasingly popular in Western cultures for its prebiotic effects. FOS serves as a substrate for microflora in the large intestine, increasing the overall gastrointestinal tract (GI Tract) health. It has also been touted as a supplement for preventing yeast infections.
Several studies have found that FOS and inulin promote calcium absorption in both the animal and human gut.The intestinal microflora in the lower gut can ferment FOS, which results in a reduced 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 can be considered a small dietary fiber with (like all fibres) low caloric value. The fermentation of FOS results in the production of gasses and acids. The latter provide some energy to the body.

# Side effects
FOS and inulin are fermented by most bacterial species in the intestine, including Klebsiella, E. coli  and many Clostridium species which are considered less-friendly bacteria in the gut. These species are mainly responsible for the gas formation (hydrogen and carbon dioxide), which results after ingestion of FOS. Most people can eat 5-10 gram of FOS without gaseous discomfort, whereas others already have problems with 1 gram. The estimated optimal dose for adult humans is around 5-10 gram/day .

# Regulation

## US FDA Regulation
FOS is generally recognized as safe (GRAS).

## NZ NZFSA Regulation
The Food Safety Authority today warned parents of babies that a major European infant formula brand made in New Zealand does not comply with local regulations, (because it contains fructo-oligosaccharides (FOS)) and urged them to stop using it.
It had been approved in the European Union for addition in restricted amounts to infant formula (for babies up to six months) and follow-on formula (for babies between six and 12 months). Infant and follow-on formula products containing FOS have been sold in the EU since 1999.