Fructooligosaccharides (FOS), also called neosugar and short-chain FOS, are non-digestible, short-chain oligosaccharides composed of D-fructose and D-glucose. FOS occur naturally in plant foods. Although FOS are non-digestible in humans, they are fermented by the colonic microflora into short-chain fatty acids. These fatty acids may have various health benefits, including antimicrobial, anticancer, hypolipidemic, hypoglycemic, anti-osteoporotic, and anti-osteopenic effects. [1-4] Commercially, FOS are combined with probiotic bacteria, used as substitute sweeteners, and are also a common ingredient in some functional food products. [1-3]
FOS are called prebiotics, because they promote the growth of beneficial bacteria, such as bifidobacteria, in the colon. FOS and other non-digestible oligosaccharides are also referred to as bifidogenic factors. FOS and bifidobacteria may inhibit the growth of detrimental bacteria such as Clostridium perfringens and Escherichia coli in the intestines. This antimicrobial activity enhances intestinal tract immunity. [1-4]
Researchers theorize that FOS may have anticancer effects in the colon through the antitumor activity of butyrate - a short chain fatty acid produced by FOS in the colon. Butyrate may also help prevent tumor growth, and cell differentiation and upregulate apoptosis. In addition, FOS may increase the concentrations of calcium and magnesium in the colon, helping to control the rate of cell turnover. [3-4] FOS may bind calcium and magnesium in the colon and facilitate their absorption, helping prevent the onset of osteoporosis and osteopenia. [3-4]
Although the mechanisms of these effects are not well understood, FOS may lower serum cholesterol and blood glucose levels. Researchers hypothesize that propionate, produced by FOS fermentation in the colon, may prevent cholesterol synthesis by inhibiting HMG-CoA reductase (a key step in cholesterol synthesis). Propionate may also prevent glucose synthesis by inhibiting pyruvate carboxylase, inducing glucose utilization by reducing free fatty acid levels, and enhancing glycolysis by lowering citrate levels in hepatocytes. [3-4]
The best natural food sources include; asparagus, garlic, Jerusalem artichokes, and onions. 
FOS are used as substitute sweeteners and have about one-half the sweetness of table sugar, or sucrose.  FOS are much lower in calories and often used in functional food products for its sweetness and health benefits. [6, 7] Although FOS occurs naturally in foods, many FOS products are still synthesized. 
As mentioned, FOS are used to encourage healthy intestinal microflora in the digestive system, to enhance intestinal tract immunity, and to improve digestive health. [5, 6, 9, 10] FOS are also sed to enhance probiotics containing beneficial bacteria such as bifidobacteria and lactobacillus. When used in combination with probiotic supplements, FOS may be helpful in the treatment of diarrhea caused by antibiotic therapy. [11, 12]
FOS may be equally useful for the treatment of high serum cholesterol and elevated blood glucose levels. Some studies have shown FOS supplementation to actually lower both of these conditions. [3, 4] One double-blind, placebo-controlled study found that treatment with a FOS-containing milk product lowered LDL cholesterol levels in borderline high cholesterol male subjects in three weeks.  However, several conflicting studies suggest that FOS may not lower serum cholesterol or blood glucose levels in type 2 diabetics. [14, 15] More research is needed to determine the hypolipidemic and hypoglycemic effects of FOS.
FOS may help protect against specific cancers, most notably, colorectal cancer. One animal study suggests that FOS may reduce the incidence of colon tumors.  However, more human studies are needed to determine the anticancer effects of FOS.
FOS may aid calcium absorption in the colon, thereby aiding the prevention bone loss. Several animal studies show that FOS may increase calcium and magnesium absorption .[17, 18] Another study suggests that FOS may prevent osteopenia after gastrectomy.  Again, more studies conducted upon human subjects are necessary to determine the anti-osteoporotic and anti-osteopenic effects of FOS.
Dosage: For prevention, tolerable dosages range from 500 - 750 milligrams (mg) daily. When used for various therapeutic applications, 2 - 3 grams per day is considered standard. [1-3]
Delivery Forms: Capsules, bulk powder.
A deficiency in FOS has not been reported in medical literature, as FOS is not a naturally occurring substance found in the human body.
FOS Toxicity: [2-4]
FOS should not be taken by those individuals with irritable bowel syndrome or a sensitivity to either dietary fiber or inulins. FOS is also contraindicated for patients receiving radiation to the gastrointestinal tract or other parts of the body. FOS doses above 10 grams daily should not be taken by those individuals with lactose intolerance. Pregnant, lactating women, and children should not take supplemental FOS, unless recommended by a health care provider.
FOS doses above 30 grams daily may cause gastrointestinal side effects including flatulence, bloating, and diarrhea.
FOS supplementation may enhance the absorption of calcium and magnesium and the possible effectiveness of probiotics.
Always inform your health care provider about the dietary supplements you are taking, since there may be a potential for side effects, interactions, or allergy.
1. Murray MT. Encyclopedia of Nutritional Supplements, NY: Three Rivers Press, 1996: 362.
2. Fructooligosaccharides, Dietary Supplement Information Bureau: http://content.nhiondemand.com/dse/consumer/monoAll-style.asp?objID=100882&ctype=ds&mtyp=4
3. Fructo-oligosaccharides, PDR Health: http://www.pdrhealth.com/drug_info/nmdrugprofiles/herbaldrugs/101840.shtml
4. Prebiotics, PDR Health: http://www.pdrhealth.com/drug_info/nmdrugprofiles/herbaldrugs/101840.shtml
5. Fishbein L, Kaplan M, Gough M. Fructooligosaccharides: a review. Vet Hum Toxicol. Apr1988;30(2):104-7.
6. Roberfroid MB. Health benefits of non-digestible oligosaccharides. Adv Exp Med Bull. 1997; 427:211-219.
7. Roberfroid MB. Prebiotics and probiotics: are they functional foods. Am Clin Nutr. 2000; 71 (6 Suppl):1682S-1687S, discussion 1688S-1690S.
8. Chiang CJ, Lee WC, Sheu DC, Duan KJ. Immobilization of beta-fructofuranosidases from Aspergillus on methacrylamide-based polymeric beads for production of fructooligosaccharides. Biotechnol Prog. Sep1997;13(5):577-82.
9. Bouhnik Y, Vahedi K, Achour L, et al. Short-chain fructo-oligosaccharide administration dose-dependently increases fecal bifidobacteria in healthy humans. J Nutr. 1999; 129:113-116.
10. Gibson GR, et al. Selective stimulation of bifidobacteria in the human colon by oligofructose and inulin. Gastroenterology 1995 (108):975-982.
11. Rolfe RD. The role of probiotic cultures in the control of gastrointestinal health. J Nutr. Feb2000;130(2S Suppl):396S-402S.
12. Tuohy KM, Kolida S, Lustenberger AM, Gibson GR. The prebiotic effects of biscuits containing partially hydrolysed guar gum and fructo-oligosaccharides–a human volunteer study. Br J Nutr. Sep2001;86(3):341-8.
13. Schaafsma G, Meuling WJ, van Dokkum W, Bouley C. Effects of a milk product, fermented by Lactobaccillus acidophilus and with fructo-oligosaccharides added, on blood lipids in male volunteers. Eur J Clin Nutr. 1998; 52:436-440.
14. Alles MS, de Roos NM, Bakx JC, et al. Consumption of fructooligosaccharides does not favorably affect blood glucose and serum lipid concentrations in patients with type 2 diabetes. Am J Clin Nutr. 1999; 69:64-69.
15. Luo J, van Yperselle M, Rizkalla SW, et al. Chronic consumption of short-chain fructooligasaccharides does not affect basal hepatic glucose production or insulin resistance in type 2 diabetics. J Nutr. 2000; 130:1572-1577.
16. Pierre F, Perrin P, Champ M, et al. Short-chain fructo-oligosaccharides reduce the occurrence of colon tumors and develop gut-associated lymphoid tissue in Min mice. Cancer Res. 1997; 57: 225-228.
17. Ohta A, Baba S, Takizawa T, Adachi T. Effects of fructo-oligasaccharides on the absorption of magnesium in the magnesium-deficient rat model. J Nutr Sci Vitaminol (Tokyo). 1994; 40:171-180.
18. Ohta A, Motohashi Y, Sakai K, et al. Dietary fructo-oligasaccharides increase calcium absorption and levels of mucosal calbindin-D9K in the large intestine of gastrectomized rats. Scand J Gastroenterol. 1998; 33:1062-1068.
19. Ohta A, Ohtsuki M, Hosoro A, et al. Dietary fructo-oligosaccharides prevent osteopenia after gastrectomy. J Nutr. 1998; 128:106-110.