Fructo-oligosaccharides (FOS) also called “prebiotics” are a group of non-digestible compounds that stimulate the growth of beneficial microflora (note: this is different than PRO-biotics, or the actual beneficial bacteria such as acidophilus and bifidum). In terms of chemistry, a fructo-oligosaccharide (FOS) is a glucose molecule bonded to multiple fructose molecules. These bonds cannot be broken down by enzymes in the human small intestine - allowing the FOS to reach the large intestine intact, where it becomes a substrate for colonic bacteria. The effects of short-chain FOS have been studied for nearly two decades. Groups of oligosaccharides can be found in foods such as beans, blueberries, and onions; a liquid supplement is available in Japan, and FOS is available in capsule form in the U.S.
Prebiotics have been shown to selectively stimulate the growth and activity of benefical bacteria in the colon. The prebiotic, fructooligosaccharide (FOS), is found naturally in many foods, such as wheat, onions, bananas, honey, garlic, and leeks – and FOS can also be isolated from chicory root or synthesized enzymatically from sucrose (both more commonly found in FOS dietary supplements). Fermentation of FOS in the colon results in a large number of physiologic effects including increasing the numbers of bifidobacteria in the colon, increasing calcium absorption, increasing fecal weight, shortening of gastrointestinal transit time, and possibly lowering blood lipid levels.
Based on the available scientific evidence, FOS supplements are generally claimed to boost levels and activity of beneficial gut bacteria and thus promote general gut health, reduce serum lipids, increase intestinal calcium absorption, alleviate antibiotic-induced diarrhea, and reduce both the severity of irritable bowel syndromes and the risk of colon cancer.
Short-chain FOS is metabolized in the colon (by colonic bacteria) into short-chain fatty acids (Giacco et al. 2004). These short-chain fatty acids cause a drop in pH, which may inhibit the growth of pathogenic bacteria, facilitate intestinal calcium absorption, and act as an energy substrate for colonic epithelial cells (Bouhnik et al. 1999, Tahiri et al. 2001). By manipulating colonic pH and microflora content, FOS may also play a protective role against colon cancer (Giacco et al. 2004, Swanson et al. 2002, Ten Bruggencate et al. 2003 and 2004). Research also points to a reduction in liver fatty acid synthesis as a possible mechanism for serum lipid reduction (Giacco et al. 2004, Swanson et al. 2002).
Human studies have shown significant increases in bifidobacteria (beneficial bacteria in the gut) from ingestion of as little as 6-8 grams of short-chain FOS per day (Chow 2002). Research has also shown decreases in pathogenic colonic bacteria from FOS ingestion (Chow 2002). There is evidence that short-chain FOS can lower cholesterol and triglycerides, but most of this research has involved animal models. Colon tumors and indicators of cancer have also been reduced in animal models. Although animal studies have given promising results, relatively few human studies have shown that mineral absorption can be enhanced from FOS ingestion (Tahiri et al. 2001).
Since the bonds of FOS are not digestible, bacterial metabolism in the large intestine produces gas and bloating. Flatulence is a common symptom associated with FOS ingestion and can be worse in people who are lactose intolerant (depending on how the FOS is processed). Studies have shown that the severity of symptoms is dose-dependent (less FOS = less symptoms). Ingestion of 20-30 grams per day has been associated with the onset of severe discomfort – but symptoms may be alleviated by starting with a small dose and increasing gradually to the desired amount (Bouhnik et al. 1999). Ten grams of FOS per day appears to be the “optimal” dose, since this amount produces a significant increase in bifidobacteria and is fairly well-tolerated.
1.Alles MS, Hautvast JG, Nagengast FM, Hartemink R, Van Laere KM, Jansen JB. Fate of fructo-oligosaccharides in the human intestine. Br J Nutr. 1996 Aug;76(2):211-21.
2.Bouhnik Y, Flourie B, Riottot M, Bisetti N, Gailing MF, Guibert A, Bornet F, Rambaud JC. Effects of fructo-oligosaccharides ingestion on fecal bifidobacteria and selected metabolic indexes of colon carcinogenesis in healthy humans. Nutr Cancer. 1996;26(1):21-9.
3.Bouhnik Y, Vahedi K, Achour L, Attar A, Salfati J, Pochart P, Marteau P, Flourie B, Bornet F, Rambaud JC. Short-chain fructo-oligosaccharide administration dose-dependently increases fecal bifidobacteria in healthy humans. J Nutr. 1999 Jan;129(1):113-6.
4.Chow J. Probiotics and prebiotics: A brief overview. J Ren Nutr. 2002 Apr;12(2):76-86.
5.Djouzi Z, Andrieux C. Compared effects of three oligosaccharides on metabolism of intestinal microflora in rats inoculated with a human faecal flora. Br J Nutr. 1997 Aug;78(2):313-24.
6.Flickinger EA, Hatch TF, Wofford RC, Grieshop CM, Murray SM, Fahey GC Jr. In vitro fermentation properties of selected fructooligosaccharide-containing vegetables and in vivo colonic microbial populations are affected by the diets of healthy human infants. J Nutr. 2002 Aug;132(8):2188-94.
7.Giacco R, Clemente G, Luongo D, Lasorella G, Fiume I, Brouns F, Bornet F, Patti L, Cipriano P, Rivellese AA, Riccardi G. Effects of short-chain fructo-oligosaccharides on glucose and lipid metabolism in mild hypercholesterolaemic individuals. Clin Nutr. 2004 Jun;23(3):331-40.
8.Gibson GR. Dietary modulation of the human gut microflora using prebiotics. Br J Nutr. 1998 Oct;80(4):S209-12.
9.Luo J, Van Yperselle M, Rizkalla SW, Rossi F, Bornet FR, Slama G. Chronic consumption of short-chain fructooligosaccharides does not affect basal hepatic glucose production or insulin resistance in type 2 diabetics. J Nutr. 2000 Jun;130(6):1572-7.
10.Moore N, Chao C, Yang LP, Storm H, Oliva-Hemker M, Saavedra JM. Effects of fructo-oligosaccharide-supplemented infant cereal: a double-blind, randomized trial. Br J Nutr. 2003 Sep;90(3):581-7.
11.Piche T, des Varannes SB, Sacher-Huvelin S, Holst JJ, Cuber JC, Galmiche JP. Colonic fermentation influences lower esophageal sphincter function in gastroesophageal reflux disease. Gastroenterology. 2003 Apr;124(4):894-902.
12.Rao AV. Dose-response effects of inulin and oligofructose on intestinal bifidogenesis effects. J Nutr. 1999 Jul;129(7 Suppl):1442S-5S.
13.Roberfroid M. Dietary fiber, inulin, and oligofructose: a review comparing their physiological effects. Crit Rev Food Sci Nutr. 1993;33(2):103-48.
14.Roberfroid MB, Van Loo JA, Gibson GR. The bifidogenic nature of chicory inulin and its hydrolysis products. J Nutr. 1998 Jan;128(1):11-9.
15.Roberfroid MB. Prebiotics and synbiotics: concepts and nutritional properties. Br J Nutr. 1998 Oct;80(4):S197-202.
16.Schaafsma G, Meuling WJ, van Dokkum W, Bouley C. Effects of a milk product, fermented by Lactobacillus acidophilus and with fructo-oligosaccharides added, on blood lipids in male volunteers. Eur J Clin Nutr. 1998 Jun;52(6):436-40.
17.Swanson KS, Grieshop CM, Flickinger EA, Bauer LL, Wolf BW, Chow J, Garleb KA, Williams JA, Fahey GC Jr. Fructooligosaccharides and Lactobacillus acidophilus modify bowel function and protein catabolites excreted by healthy humans. J Nutr. 2002 Oct;132(10):3042-50.
18.Tahiri M, Tressol JC, Arnaud J, Bornet F, Bouteloup-Demange C, Feillet-Coudray C, Ducros V, Pepin D, Brouns F, Rayssiguier AM, Coudray C. Five-week intake of short-chain fructo-oligosaccharides increases intestinal absorption and status of magnesium in postmenopausal women. J Bone Miner Res. 2001 Nov;16(11):2152-60.
19.Ten Bruggencate SJ, Bovee-Oudenhoven IM, Lettink-Wissink ML, Katan MB, Van Der Meer R. Dietary fructo-oligosaccharides and inulin decrease resistance of rats to salmonella: protective role of calcium. Gut. 2004 Apr;53(4):530-5.
20.Ten Bruggencate SJ, Bovee-Oudenhoven IM, Lettink-Wissink ML, Van der Meer R. Dietary fructo-oligosaccharides dose-dependently increase translocation of salmonella in rats. J Nutr. 2003 Jul;133(7):2313-8.
21.van Dokkum W, Wezendonk B, Srikumar TS, van den Heuvel EG. Effect of nondigestible oligosaccharides on large-bowel functions, blood lipid concentrations and glucose absorption in young healthy male subjects. Eur J Clin Nutr. 1999 Jan;53(1):1-7.
EDITOR'S NOTE: This monograph can be found in The Health Professional's Guide to Dietary Supplements (Lippincott, Williams & Wilkins) by Shawn M. Talbott, PhD and Kerry Hughes, MS.