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Fructo-oligosaccharides (FOS)

Supplement Forms/Alternate Names

  • FOS
  • Galacto-oligosaccharides
  • Inulin
  • GOS
  • Prebiotics

Fructo-oligosaccharides (FOS) are starches that the human body cannot fully digest. Inulin and galacto-oligosaccharides (GOS) are similar substances also discussed in this article.

When a person consumes FOS, the undigested portions provide nourishment for bacteria in the digestive tract. “Friendly” bacteria ( probiotics ) may respond particularly well to this nourishment. Because FOS feed probiotics, they are sometimes called a “prebiotic.”

Low doses of FOS are often provided along with probiotic supplements to aid their growth. High doses of FOS (and related substances) have been advocated for a variety of health conditions. However, currently, the available scientific evidence for benefit remains more negative than positive.


There is no daily requirement for FOS. FOS and related substances are found in asparagus, Jerusalem artichoke, leeks, onions, and soybeans, among other foods.

Therapeutic Dosages

When taken simply for promoting healthy bacteria, FOS are often taken at a dose of 4-6 g daily. When used for therapeutic purposes, the typical dose of FOS is 10-20 g daily, divided into three doses and taken with meals. Side effects are common at a daily intake 15 g or more (see Safety Issues ).

Therapeutic Uses

Animal studies hint that FOS, GOS, and inulin can significantly improve cholesterol profile; however, study outcomes in humans have been inconsistent at best. 1-7 One study found that while inulin might produce a short-term benefit, any such benefit disappears after six months of use. 18

At most, it appears that FOS might improve cholesterol profiles by 5%, an amount too small to make much of a difference in most circumstances. These relatively poor results might be due to that fact that humans cannot tolerate doses of FOS much above 15 g daily without developing gastrointestinal side effects.

FOS has also been suggested for preventing traveler’s diarrhea . However, in a large (244-participant) double-blind study, FOS at a dose of 10 g daily again offered only minimal benefits. 8Probiotics themselves might be a better bet.

Another study found that use of FOS might help reduce incidents of diarrhea, flatulence, and vomiting in preschoolers. 16

According to most studies, FOS at 10-20 g daily do not improve blood sugar control in people with type 2 diabetes . 9,10

FOS have been advocated as a treatment for irritable bowel syndrome . However, research results are currently inconsistent at best. For example, a 6-week, double-blind study of 105 people with mild irritable bowel syndrome compared 5 g of fructo-oligosaccharides daily against placebo, and returned conflicting results. 19 According to some measures of symptom severity employed by the researchers, use of FOS led to an improvement in symptoms. However, according to other measures, FOS actually worsened symptoms. Conflicting results, though of a different kind, were also seen in a 12-week, double-blind, placebo-controlled study of 98 people. 11 Treatment with FOS at a dose of 20 g daily initially worsened symptoms, but over time this negative effect wore off. At no time in the study were clear benefits seen, however. On a positive note, one study did find benefit with a combination prebiotic-probiotic formula, 20 and another study found the combination beneficial for women with constipation when taken in yogurt. 22

Small double-blind studies found that FOS at a dose of 10 g daily may improve magnesium absorption in postmenopausal women. 12 Whether this is beneficial remains unclear, since magnesium deficiency is not believed to be a widespread problem. FOS may also slightly increase copper absorption , but does not appear to affect absorption of calcium , zinc , or selenium . 13,14

A randomized, placebo-controlled trial, involving 134 infants less than 6 months old whose parents suffered from allergies, found that those fed a prebiotic combination of FOS/GOS experienced a significant reduction in both allergy symptoms and minor infections that lasted at least through age 2. The researchers suggested that the favorable effects of prebiotics on intestinal bacteria early in life may produce lasting benefits to the immune system. 21

One study found that use of inulin promoted growth of probiotic bacteria in the bifidobacteria family. 17

Safety Issues

FOS appear to be generally safe. However, they can cause bloating, flatulence, and intestinal discomfort, especially when taken at doses of 15 g or higher daily. 6,7 People with lactose intolerance may particularly suffer from these side effects. 15

Revision Information

  • 1

    Davidson MH, Synecki C, Maki KC, Drennen KB. Effects of dietary inulin in serum lipids in men and women with hypercholesterolaemia. Nutr Res . 1998;3:503-517.

  • 2

    Giacco R, Clemente G, Luongo D, et al. Effects of short-chain fructo-oligosaccharides on glucose and lipid metabolism in mild hypercholesterolaemic individuals. Clin Nutr . 2004;23:331-340.

  • 3

    Jackson KG, Taylor GRJ, Clohessy AM, Williams CM. The effect of the daily intake of inulin on fasting lipid, insulin and glucose concentrations in middle-aged men and women. Br J Nutr . 1999;82:23-30.

  • 4

    Pedersen A, Sandstrom B, van Amelsvoort JMM. The effect of ingestion of inulin on blood lipids and gastrointestinal symptoms in healthy females. Br J Nutr . 1997;78:215-222.

  • 5

    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;52:436-440.

  • 6

    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;53:1-7.

  • 7

    Williams CM, Jackson KG. Inulin and oligofructose: effects on lipid metabolism from human studies. Br J Nutr . 2002;87(suppl 2):S261-264.

  • 8

    Cummings JH, Christie S, Cole TJ. A study of fructo oligosaccharides in the prevention of travellers' diarrhoea. Aliment Pharmacol Ther . 2001;15:1139-1145.

  • 9

    Luo J, Van Yperselle M, Rizkalla SW, et al. Chronic consumption of short-chain fructooligosaccharides does not affect basal hepatic glucose production or insulin resistance in type 2 diabetics. J Nutr . 2000;130:1572-1577.

  • 10

    Alles MS, de Roos NM, Bakx JC, van de Lisdonk E, Zock PL, Hautvast GA. 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.

  • 11

    Olesen M, Gudmand-Hoyer E. Efficacy, safety, and tolerability of fructooligosaccharides in the treatment of irritable bowel syndrome. Am J Clin Nutr . 2000;72:1570-1575.

  • 12

    Tahiri M, Tressol JC, Arnaud J, et al. Five-week intake of short-chain fructo-oligosaccharides increases intestinal absorption and status of magnesium in postmenopausal women. J Bone Miner Res . 2001;16:2152-2160.

  • 13

    Tahiri M, Tressol JC, Arnaud J, et al. Effect of short-chain fructooligosaccharides on intestinal calcium absorption and calcium status in postmenopausal women: a stable-isotope study. Am J Clin Nutr . 2003;77:449-457.

  • 14

    Ducros V, Arnaud J, Tahiri M, et al. Influence of short-chain fructo-oligosaccharides (sc-FOS) on absorption of Cu, Zn, and Se in healthy postmenopausal women. J Am Coll Nutr . 2005;24:30-37.

  • 15

    Teuri U, Vapaatalo H, Korpela R. Fructooligosaccharides and lactulose cause more symptoms in lactose maldigesters and subjects with pseudohypolactasia than in control lactose digesters. Am J Clin Nutr . 1999;69:973-979.

  • 16

    Waligora-Dupriet AJ, Campeotto F, Nicolis I, et al. Effect of oligofructose supplementation on gut microflora and well-being in young children attending a day care centre. Int J Food Microbiol . 2006 Sep 20. [Epub ahead of print]

  • 17

    Bouhnik Y, Raskine L, Champion K, et al. Prolonged administration of low-dose inulin stimulates the growth of bifidobacteria in humans. Nutr Res. 2007;27:187-193.

  • 18

    Forcheron F, Beylot M. Long-term administration of inulin-type fructans has no significant lipid-lowering effect in normolipidemic humans. Metabolism. 2007;56:1093-1098.

  • 19

    Paineau D, Payen F, Panserieu S, et al. The effects of regular consumption of short-chain fructo-oligosaccharides on digestive comfort of subjects with minor functional bowel disorders. Br J Nutr. 2007 Aug 13. [Epub ahead of print]

  • 20

    Bittner AC, Croffut RM, Stranahan MC, et al. Prescript-Assist probiotic-prebiotic treatment for irritable bowel syndrome: a methodologically oriented, 2-week, randomized, placebo-controlled, double-blind clinical study. Clin Ther. 2005;27:755-761.

  • 21

    Arslanoglu S, Moro GE, Schmitt J, et al. Early dietary intervention with a mixture of prebiotic oligosaccharides reduces the incidence of allergic manifestations and infections during the first two years of life. J Nutr. 2008;138:1091-1095.

  • 22

    De Paula JA, Carmuega E, Weill R. Effect of the ingestion of a symbiotic yogurt on the bowel habits of women with functional constipation. Acta Gastroenterol Latinoam. 2008;38:16-25.