FOS (fructooligosaccharides)

Fructooligosaccharides (FOS)

1. Identity: Chemical Names, Botanical Sources, and Common Forms

Chemical Identity and Nomenclature

FOS is a type of oligosaccharide defined as nondigestible carbohydrates consisting of glucose and fructose sugar molecules connected by β(2→1) glycosidic bonds and a degree of polymerization that varies from 2 to 60 chain lengths. FOS is commonly referred to as oligofructose, oligofructan, fructose oligomers, fructans, and glycofructans. On a chemical note, fructooligosaccharides are polymers with a sucrose molecule further elongated by a chain of fructosyl residues, with the general structure GFn (where G corresponds to a glucose residue, F is a fructose residue, and n is the number of fructose residues).

FOS is a series of homologous oligosaccharides derived from sucrose, usually denoted by the chemical formula GFn: (A) 1-kestose (GF2); (B) nystose (GF3); (C) 1F-β-fructofuranosyl nystose (GF4). The main components of commercial products are kestose (GF2), nystose (GF3), fructosylnystose (GF4), bifurcose (GF3), inulobiose (F2), inulotriose (F3), and inulotetraose (F4). The fructosyl-glucosyl linkage is always β-(2→1) as in the case of sucrose, while the fructosyl-fructosyl linkages are either β-(1→2) or β-(6→2). The branched fructans have β-(2→6) linkages.

Because of the configuration of their glycosidic 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, while contributing to the dietary fiber fraction of the diet. FOS provides approximately 1.5 kcal/g, making it ideal for sugar-free formulations.

FOS exhibits sweetness levels between 30 and 50 percent of sugar in commercially prepared syrups. Fructooligosaccharides are more soluble than inulins and are, therefore, sometimes used as an additive to yogurt and other (dairy) products. Fructooligosaccharides are used especially in combination with high-intensity artificial sweeteners, whose sweetness profile and aftertaste they improve.

Natural Botanical Sources

FOS is extracted from the blue agave plant as well as fruits and vegetables such as bananas, onions, chicory root, garlic, asparagus, jícama, and leeks. Some grains and cereals, such as wheat and barley, also contain FOS. The Jerusalem artichoke and its relative yacón together with the blue agave plant have been found to have the highest concentrations of FOS of cultured plants. FOS can be found in approximately 36,000 different plants, cereals, and honey; however, these sources only provide trace amounts of FOS, resulting in the need for commercial production.

FOS are produced by fructosyltransferase (FTase) derived from some plants such as Jerusalem artichoke, chicory, asparagus, banana, dragon fruit, and onion. The enzyme sucrose:sucrose fructosyltransferase is responsible for the production of the smallest fructooligosaccharide, 1-kestose, directly from two units of sucrose in plants such as onion.

Commercial Production and Forms

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 β(2→1) bonds with a terminal α(1→2) linked D-glucose. The degree of polymerization of inulin ranges from 10 to 60. Inulin can be degraded enzymatically or chemically to a mixture of oligosaccharides with the general structure Glu–Frun (abbrev. GFn) and Frum (Fm), with n and m ranging from 1 to 7.

The second class of FOS is prepared by the transfructosylation action of a β-fructosidase of Aspergillus niger or Aspergillus on sucrose. The resulting mixture has the general formula of GFn, with n ranging from 1 to 5. Contrary to the inulin-derived FOS, not only is there β(1→2) binding but other linkages do occur, however, in limited numbers.

Naturally present in various fruits and vegetables, FOSs are primarily produced enzymatically or microbially from sucrose or long-chain fructans, namely inulin. Enzymes such as fructosyltransferase, β-fructofuranosidase, and endoinulinase are typically involved in its production. The commercially available FOS preparations being used for their prebiotic properties belong particularly to the inulin type and show low degree of polymerization (DP), ranging from 3 to 9.

The increasing consumer demand for healthy foods has driven the widespread use of FOSs in the functional food industry. Thus, FOSs have been incorporated into dairy products, beverages, snacks, and pet foods. FOS is currently being incorporated into various food applications such as formula for infants, baby food, dairy products, meat/fish/poultry products, confectionary/candy, cereal products, beverages, cookies, crackers, bakery products, food supplements, and processed foods throughout the US and Europe.

2. Traditional and Historical Use

The history of fructooligosaccharides dates back to over 150 years ago. The modern history of fructans came into existence with their discovery by Rose (1804). Although FOS as an isolated compound was only identified and named in the 20th century, the traditional consumption of FOS-rich foods has occurred for thousands of years across cultures.

Chicory root, one of the richest natural sources of FOS and inulin, was used in Ancient Egypt, Greece, and Rome as a liver tonic and digestive aid. Garlic and onions, staples in global cuisines, were also used medicinally for digestion, immunity, and circulation—delivering FOS alongside other bioactive compounds.

In Traditional Chinese Medicine, herbs like Chinese yam and burdock, which contain FOS and other fermentable fibers, were used to tonify the Spleen and Stomach, support Qi, and relieve constipation. Similarly, Jerusalem artichoke, another FOS-rich plant, has been used in European folk remedies for blood sugar and gut health.

For centuries, levan-FOS has been part of the human diet of many cultures. Their role as healthy molecules has been historically demonstrated.

FOS use as an isolated ingredient emerged in the 1980s in response to consumer demand for healthier and calorie-reduced foods. The commercial introduction of FOS occurred in the 1980s through the efforts of Meiji Seika Kaisha in Japan. FOS has been a popular sweetener in Japan and Korea for many years, even before 1990, when the Japanese government installed a "Functionalized Food Study Committee" of 22 experts to start to regulate "special nutrition foods or functional foods." The modern scientific recognition of FOS began in Japan in the 1980s, where researchers explored its prebiotic effects as part of the country's development of functional food science.

Meiji Seika Ltd. of Japan commercialized fructooligosaccharides production from sucrose by the action of Aspergillus niger β-fructofuranosidase. By 1990, the FOS market had grown to over 4,000 metric tons, finding their way into all sorts of food and health products.

3. Key Constituents and Mechanisms of Action

Primary Constituent Molecules

FOSs are short-chain fructose-based oligosaccharides with notable functional and health benefits. The three principal oligomers present in typical commercial scFOS preparations are 1-kestose (GF2), nystose (GF3), and 1F-β-fructofuranosyl nystose (GF4). Short-chain FOS (scFOS) are more rapidly and selectively fermented by beneficial bacteria such as Bifidobacteria compared to longer-chain inulin.

Resistance to Digestion

FOS endure hydrolysis through saliva and intestinal digestive enzymes due to the formation of their glycosidic bonds. These are fermented in the intestine by anaerobic bacteria, which contributes to enhanced bioavailability of dietary fiber and a low caloric value. Digestible carbohydrate is digested in the upper gastrointestinal tract and provides energy. Non-digestible saccharide passes intact through the upper tract and is fermented in the colon to give physiological responses.

Bifidogenic (Selective Fermentation) Effect

The use of FOS as a dietary supplement has been associated with an increase in the abundance of the Bifidobacterium genus, which is an important member of the gut microbial community starting from birth and continuing onward throughout the aging process. This bifidogenic property of FOS when used as a prebiotic has been demonstrated by several recent studies involving human participants.

Studies consistently report an increase in beneficial bacteria, particularly Bifidobacterium and Lactobacillus, leading to higher production of short-chain fatty acids (SCFAs) such as acetate, propionate, and butyrate. These metabolic changes are linked to improved integrity of the epithelial barrier, reduced inflammatory signaling, modulation of immune responses, and enhanced metabolic balance.

Short-Chain Fatty Acid (SCFA) Production

The changes to the gut microbial community caused by ingestion of FOS also cause changes in the metabolic products of that community, especially the production of short-chain fatty acids (SCFAs). SCFAs are the driver of many of the beneficial health effects associated with the gut microbial community including glucose homeostasis, the integrity of the gastrointestinal tract, and host immunity.

The fermentation of dietary fibers into short-chain fatty acids (SCFAs) by the gut microbiota can promote intestinal peristalsis by activating receptors in 5-hydroxytryptamine (5-HT)-producing cells and increasing the synthesis and release of 5-HT. SCFAs play a crucial role in gut health and have extra-intestinal metabolic effects beyond the intestines, such as regulating glucose homeostasis, lipid metabolism, immune function, and appetite.

For mucosa, butyrate serves as a fuel, and propionate and acetate enter portal blood and influence lipid and carbohydrate metabolism.

Mineral Absorption Enhancement

The intestinal fermentation of FOS results in the production of SCFAs which decrease pH and promote calcium and magnesium absorption in both animals and in human clinical studies. FOS also have an increasing effect on the intestinal absorption of calcium (Ca), magnesium (Mg), and iron.

Lipid Metabolism

FOS fermentation increases the SCFA in the intestine, which helps to reduce the level of triglycerols and cholesterol, indicating the importance of FOS in managing hypercholesterolaemia. It is proposed that FOS may increase fecal cholesterol excretion by stimulating bacterial growth, which in turn decreases the blood cholesterol level.

4. Scientific Evidence by Area of Use

4.1 Gut Microbiota Modulation (Prebiotic Effect)

Inulin-type fructans (ITF), including short-chain fructooligosaccharides (scFOS), oligofructose, and inulin, are commonly used fibers that are widely regarded as prebiotic for their ability to be selectively utilized by the intestinal microbiota to confer a health benefit.

A landmark dose-response human RCT published in Scientific Reports (2019) directly investigated the bifidogenic effect of FOS. This study investigated these aspects through a randomized, double-blind, placebo-controlled, dose-response relationship study. The study involved 80 participants being administered FOS at three dose levels (2.5, 5, and 10 g/day) or placebo (Maltodextrin 10 g/day) during the dosage phase. Microbial DNA extracted from fecal samples collected at 9 intervening time-points was sequenced and analysed.

Prebiotics such as inulin, galactooligosaccharides (GOS), and fructooligosaccharides (FOS) can positively influence the gut microbiota by promoting beneficial bacteria like Bifidobacteria. Fructooligosaccharides (FOS) are well-known carbohydrates that promote healthy gut microbiota and have been previously demonstrated to enhance levels of Bifidobacterium and Lactobacillus.

The systematic review by Hughes et al. (2021, PMC) examined the prebiotic potential of inulin-type fructans across human clinical trials. Their review discussed beneficial effects on intestinal microbiota composition and intestinal and extraintestinal processes, including glucose homeostasis, lipids, mineral absorption and bone health, appetite and satiety, inflammation and immune function, and body composition.

Evidence strength: The bifidogenic effect of FOS is among the most consistently demonstrated effects in human clinical trials. Multiple RCTs and systematic reviews support selective increases in Bifidobacterium counts following FOS supplementation. This is considered the best-established mechanism and outcome for FOS as a prebiotic.

4.2 Constipation and Bowel Function

A 2024 systematic review and meta-analysis of RCTs, published in Foods (MDPI) and indexed in PMC, specifically examined FOS and functional constipation. The study set out to investigate the usefulness of consuming FOS as a dietary supplement on bowel movement frequency, stool consistency, abundance of Bifidobacteria, gastrointestinal transit time, and gastrointestinal symptoms through a systematic review and meta-analysis of RCTs. The databases searched included the Cochrane Library, PubMed, EMBASE, and Web of Science up to 2 March 2024. RCTs reporting the use of FOS as a supplement were included, with bias risk assessed using the Cochrane Risk of Bias assessment tool. The meta-analysis encompassed 17 randomized controlled trials, involving a total of 713 study participants.

Overall, the intake of FOS significantly increased bowel movement frequency (95% CI: 0.80, 1.50, p < 0.00001) and positively affected stool consistency, softening the stool (SMD: 0.36, 95% CI: 0.12, 0.60, p = 0.76). It also reduced the effort and pain during defecation (SMD: −0.60, 95% CI: −0.85, −0.34, p = 0.12). Mild bloating was noted as an adverse event associated with FOS ingestion (OR: 10.36, 95% CI: 3.32, 33.23, p = 0.24). No reports of serious adverse events were documented. Overall, FOS may enhance bowel movement frequency, stool consistency, and overall constipation symptoms, suggesting cautious optimism regarding their use as a dietary treatment alternative. Nevertheless, further robust and definitive randomized controlled trials are required to more accurately determine the most effective dosage and duration of use.

A separate clinical study in elderly continuous ambulatory peritoneal dialysis patients also found benefit: Fructo-oligosaccharides significantly increased the frequency of defecation (10.5 ± 2.0 vs 6.2 ± 1.4 times per week, p < 0.005) and changed the feces' appearance.

Evidence strength: Moderate-to-good. The 2024 meta-analysis of 17 RCTs (713 participants) supports benefit for constipation, but the authors note ongoing need for larger, better-powered trials and standardized dosing protocols.

4.3 Glucose Homeostasis and Metabolic Health

Despite promising preclinical findings, clinical evidence on the long-term metabolic effects of scFOS in at-risk populations remains limited and inconclusive. Clinical trials with other prebiotic fibers such as inulin and oligofructose have yielded inconsistent results, with outcomes varying depending on the population studied, dietary context, type and dose of prebiotic, and intervention duration.

A systematic review and meta-analysis of animal studies reported significant reductions in fasting glycemia following FOS intake, particularly in models of impaired glucose homeostasis or presenting obesity. However, the translation to human populations is less clear. The role of FOS in reducing plasma glucose and cholesterol has been studied widely; however, the results remain inconclusive.

Short-chain fatty acids, mainly acetate and propionate, are produced and absorbed during the process of colonic fermentation. These short-chain fatty acids can reduce plasma-free fatty acids, which might theoretically lower blood sugar and increase insulin sensitivity.

A 2025 Frontiers in Nutrition randomized, double-blinded, placebo-controlled study was described as among the few to simultaneously assess the effects of scFOS over a 12-week period on gut microbiota composition, glucose homeostasis, and body composition in individuals who are not yet clinically diabetic. Prior human data include a noted 1996 study from the American Journal of Clinical Nutrition documenting that chronic consumption of short-chain fructooligosaccharides by healthy subjects decreased basal hepatic glucose production but had no effect on insulin-stimulated glucose metabolism. A 2000 study in the Journal of Nutrition similarly found that chronic consumption of short-chain fructooligosaccharides does not affect basal hepatic glucose production or insulin resistance in type 2 diabetics.

FOS are not able to reduce the concentration of serum lipid in subjects having normal levels of lipids, but in patients having uncontrolled diabetes and hyperlipidemia, they have moderate effects.

Evidence strength: Preliminary to weak in humans. Animal models show consistent glucose-lowering effects, but human RCTs have yielded inconsistent results, particularly in non-diabetic populations. Evidence is stronger for individuals with existing dysglycemia or hyperlipidemia.

4.4 Lipid Metabolism and Cardiovascular Risk Markers

Food industries are highly interested in developing functional food ingredients to mitigate the risk of cardiovascular diseases by controlling serum lipids. Studies conducted in insulin-resistant rats reported that daily FOS consumption enhanced HDL cholesterol levels and decreased LDL cholesterol and steatosis. FOS supplementation has been reported to effectively reduce hepatic steatosis in animal models. FOS fermentation increases the SCFA in the intestine, which helps to reduce the level of triglycerols and cholesterol, indicating the importance of FOS in managing hypercholesterolaemia.

The mechanism by which FOS reduces cholesterol levels remains to be investigated. It is proposed that FOS may increase fecal cholesterol excretion by stimulating bacterial growth, which in turn decreases the blood cholesterol level. However, in clinical studies, FOS failed to show hypoglycemic and hypocholesterolemic effects in some populations, as these parameters did not change throughout certain studies. One study found no reduction in abnormal high levels of glucose and lipid levels after FOS supplementation at 15 g/d for 20 days.

Evidence strength: Preliminary in humans. Positive results in rodent and in vitro models, but human RCT evidence for lipid-lowering is mixed and does not currently support definitive conclusions for normolipidemic individuals.

4.5 Mineral Absorption and Bone Health

Important findings have accumulated from animal studies showing that fermentable complex carbohydrates, potato-resistant starch, inulin, and oligosaccharides, in particular fructooligosaccharides (FOSs), may enhance intestinal absorption of calcium and magnesium and probably that of some trace elements such as iron and zinc.

A human clinical study in postmenopausal women — a population at elevated risk for decreased calcium absorption — investigated the effect of short-chain FOS using stable isotope methodology. Fourteen healthy, postmenopausal women were recruited and 12 completed the study. Subjects were included if they were 50–70 years of age, had been going through menopause for more than 2 years, and were not receiving hormonal replacement therapy. A separately referenced RCT in the Journal of Nutrition (2014, Slevin et al.) examined postmenopausal women receiving calcium and short-chain FOS and found that supplementation with calcium and short-chain fructo-oligosaccharides affects markers of bone turnover but not bone mineral density in postmenopausal women.

Fructooligosaccharides (FOS) are well known as prebiotics that improve intestinal microflora. FOS also have an increasing effect on the intestinal absorption of calcium (Ca), magnesium (Mg), and iron. These effects were inspected by many animal experiments and then by human studies.

Regarding iron: A 2022 study published in the Journal of Nutrition (Giorgetti et al.) found that prebiotic galacto-oligosaccharides and fructo-oligosaccharides, but not acacia gum, increase iron absorption from a single high-dose ferrous fumarate supplement in iron-depleted women.

Evidence strength: Moderate for calcium absorption enhancement in both animal and limited human studies. Bone mineral density endpoints in humans show improvement of turnover markers in some RCTs, but direct increases in BMD have not been consistently demonstrated in clinical trials. Iron absorption evidence from at least one human RCT is positive.

4.6 Immune Function

A systematic review assessed the scientific evidence from human studies on the effects of prebiotics and non-digestible carbohydrates on markers of immunity and inflammation, infection risk and severity, and the response to vaccination in healthy individuals. A comprehensive search of PubMed, Scopus, and Embase was conducted to identify randomized, controlled trials published up to January 28th, 2025.

The bifidogenic properties of FOS are associated with positive health outcomes such as reduced obesity and anti-inflammatory properties, and therefore FOS is in use as a prebiotic supplement to support healthy gut microbiota.

In the infant population, a randomized, double-blind, placebo-controlled trial (Paineau et al., J. Nutr. Sci. Vitaminol., 2014) examined the effects of short-chain fructooligosaccharides on faecal bifidobacteria and specific immune response in formula-fed term infants. FOS administration with Bifidobacterium longum has been reported to reduce tumor necrosis factor type-alpha, C-reactive protein, serum aspartate aminotransferase levels, homeostasis model of assessment-insulin resistance, serum endotoxin, steatosis, and the pathogenesis of non-alcoholic steatohepatitis activity index in patients.

Evidence strength: Preliminary to moderate. While mechanistic evidence for immune modulation via SCFA and microbiota pathways is strong, direct evidence from well-powered human RCTs specifically targeting immune endpoints remains an active area requiring further research.

4.7 Infant Nutrition

FOS are considered prebiotics and their use in infant formulas is due to their positive effects on gastrointestinal function. They are reported to increase the fecal Bifidobacterium content to improve problems such as constipation in children that were not breast fed.

A randomized, double-blind, 28-day parallel feeding trial in newborn infants examined soy formula supplemented with scFOS at 2.5 g/L. Results indicated no significant study group differences in study completion rates, growth, mean rank stool consistency, stool frequency, formula intake, spit-up/vomit, and safety measures.

The doses used in research for infants are 4 grams of FOS per liter of formula, or up to 1 gram of FOS per kilogram of infant body weight.

Evidence strength: Moderate. FOS has an established record of use in infant formula research. Evidence supports bifidogenic effects and stool softening in formula-fed infants, though the regulatory landscape for FOS in infant formula varies by jurisdiction.

4.8 Travelers' Diarrhea

FOS may also offer some protective benefits against travelers' diarrhea, though evidence from studies shows limited effectiveness. This area remains one of the less-established potential applications, with insufficient RCT evidence to draw firm conclusions.

5. Body Systems Associated with FOS

• Gastrointestinal system: Selective modulation of colonic microbiota (bifidogenic effect); promotion of bowel regularity; SCFA-mediated maintenance of intestinal epithelial integrity; reduction of constipation symptoms.
• Metabolic/endocrine system: Potential modulation of postprandial glycemia and insulin sensitivity via SCFA-mediated pathways; hepatic glucose production; lipid metabolism.
• Skeletal system: Enhancement of calcium and magnesium absorption via colonic acidification; potential effects on bone turnover markers.
• Immune system: Indirect immunomodulation via gut microbiota and SCFA production; modulation of inflammatory cytokines.
• Cardiovascular system: Proposed cholesterol-lowering via fecal sterol excretion and SCFA-mediated lipogenesis inhibition (evidence primarily preclinical).

6. Dosage Forms and Doses Reported in Studies

FOS has most often been used by adults in doses of 10 grams by mouth daily for up to 4 weeks in clinical studies.

In the United States, FOS is available as a nutritional supplement at recommended doses of up to 4–8 g/day to promote the growth of bifidobacteria.

The dose-response RCT by the Scientific Reports study administered FOS to human subjects at three dose levels (2.5, 5, and 10 g/day) or placebo (maltodextrin 10 g/day) during the dosage phase.

The doses used in research for infants are 4 grams of FOS per liter of formula, or up to 1 gram of FOS per kilogram of infant body weight.

The estimated daily intake of FOS is in the range of 6.2 g/day (mean consumer) to 12.8 g/day (90th percentile consumer) in food excluding infants. The addition of FOS at levels up to 20 g/day in conventional foods for the general population and at levels up to 4.2 g/day in infant foods is considered safe.

Regarding upper limits of tolerability, tolerability studies of FOS indicate that 20 grams FOS per day causes mild gastrointestinal symptoms and that 30 grams FOS per day causes major discomfort and gastrointestinal symptoms.

Currently, there is no established daily recommended dosage for FOS. FOS preparations are available commercially as powders, syrups, capsules, and tablets, as well as incorporated into functional foods, dairy products, infant formulas, and dietary supplement blends.

7. Safety Considerations and Notable Interactions

Regulatory Status

FOS is classified as generally recognized as safe (GRAS). Short-chain FOS are being used as functional food and feed ingredients in Europe, America, and Asia due to their GRAS status and have received considerable attention in the nutraceutical sector. The FDA has received GRAS notifications for FOS preparations for intended use in conventional foods including infant formula, based on scientific procedures.

Gastrointestinal Side Effects

The results of clinical meta-analysis indicated that consuming FOS can result in adverse effects such as flatulence and bloating; however, all studies indicated that these adverse effects were within tolerable limits. As a prebiotic, FOS is utilized by the gut microbiota, leading to gas production during fermentation, which may cause bloating.

Tolerability studies of FOS indicate that 20 grams FOS per day causes mild gastrointestinal symptoms and that 30 grams FOS per day causes major discomfort and gastrointestinal symptoms.

Contraindications and Populations Requiring Caution

FOS are not well tolerated in individuals with Irritable Bowel Syndrome (IBS) or with FODMAP sensitivity. FODMAP represents fermentable oligosaccharides, disaccharides, monosaccharides, and polyols, which are short-chain carbohydrates that are poorly absorbed by the small intestine. Due to much of the existing research suggesting that negative side effects of consumption of FODMAP are common, the low FODMAP diet serves as a second-line dietary intervention for patients with irritable bowel syndrome (IBS). Because FOS are classified as oligosaccharides within the FODMAP framework, they can exacerbate symptoms in FODMAP-sensitive individuals.

Severe small intestinal bacterial overgrowth (SIBO) is a condition where fermentable substrates may worsen bacterial overgrowth symptoms.

Toxicological Profile

In acute and 14-day studies, administration of FOS (FOSSENCE™) to Wistar rats did not cause any mortality or clinical signs and changes in body weights, feed consumption, and gross pathology at the doses of 2000, 5000, and 9000 mg/kg body weight. In the subchronic (90-day) toxicity study, FOSSENCE™ was administered by oral gavage to Wistar rats at the doses of 0, 2000, 5000, and 9000 mg/kg/day for 90 days. No treatment-related clinical signs or mortalities were observed.

Carcinogenicity

Reviews published in Veterinary and Human Toxicology indicate FOS are not linked to cancer and are not toxic to humans or animals.

Infant Formula Regulatory Considerations

The Food Safety Authority warned parents of babies that a major European baby-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. This reflects the fact that regulatory authorization for FOS in infant formula differs by country and regulatory body, and compliance with local standards is required.

Interactions

No well-documented pharmacokinetic drug interactions with FOS have been established in clinical studies indexed in PubMed or NIH databases. The primary concern is the potential for FOS to serve as a substrate for pathogenic as well as beneficial bacteria. Since FOS feed bacteria, there is also the chance that they can feed unfriendly bacteria in the gut. In clinical practice, FOS is often provided along with probiotic supplements at low doses to aid their growth. The clinical significance of any interaction between FOS and medications that alter gut flora (e.g., antibiotics) has not been formally characterized in human trials. Antibiotic-induced dysbiosis would be expected to reduce the prebiotic efficacy of FOS during the course of antibiotic therapy.

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