IngredientsGlucooligosaccharides (abbreviated GlcOS) are a broad class of short-chain carbohydrate polymers composed exclusively of d-glucose (glucopyranose) units joined by one or more O-glycosidic linkages. The term functions as a family name encompassing numerous structurally distinct subclasses rather than a single compound. GlcOS with 2–10 glucose residues and one or more O-glycosidic linkage(s) have been found to exert prebiotic potentials because of their selective fermentation by beneficial gut bacteria. The most widely studied and commercially relevant subclasses include:
GlcOS are glucose polymers of the general formula [O-α-D-glucopyranosyl]n where n is an integer from 2 to 10. Structurally, synthesized GlcOS are mainly short-chain oligomers with a degree of polymerization (DP) between 2 and 4, with a small percentage of larger oligosaccharides (DP 5–9), linked by predominantly α- and β-(1→6) linkages along with (1→4), (1→3), (1→2), and (1↔1) linkages.
IMOs are oligosaccharides comprising less than 10 glucose monomers linked by α-(1→4) and α-(1→6) glycosidic linkages. The IMO subgroup is a blend of alpha-D-linked glucose oligomers, including isomaltose, panose, isomaltotetraose, isomaltopentaose, nigerose, kojibiose, isopanose, and higher branched oligosaccharides.
GlcOS are not abundant as isolated compounds in nature; rather, small quantities arise as by-products of microbial fermentation and enzymatic activity on starch-containing substrates. In fermented foods such as miso, sake, soy sauce, beer, and honey, minimal concentrations of naturally occurring IMOs can be observed. IMOs are also found naturally in kimchi and sourdough bread and commercially from starch-derived sources.
Certain GlcOS subclasses are derived from plant and fungal polysaccharides. GlcOS derived from β-glucans, such as laminarin (mixed β-(1→3) and β-(1→6) glucan), curdlan (β-(1→3) glucan), and barley/oat/cereal (mixed β-(1→3) and β-(1→4) glucans), are reported as potential functional oligosaccharides. Notably, α-(1→3)-glucooligosaccharides have been obtained by acid hydrolysis of α-(1→3)-d-glucan isolated from the fruiting bodies of the polypore fungus Laetiporus sulphureus.
Other α- or β-glucans such as dextran, curdlan, and laminarin are seldomly used as substrates to produce GlcOS mainly because they are not naturally abundant. Consequently, the vast majority of GlcOS used commercially and in research are manufactured by enzymatic or chemical processes rather than extracted directly from natural sources.
IMOs were originally developed in Japan for use in the Asian market and are now available worldwide in syrup or powder form, characterized by low calories and a mildly sweet taste. IMOs are used as bulking agents to increase the fiber content of food. IMOs' versatile functionality as a food ingredient, pharmaceutical, and cosmetic precursor results from their small molecular size, yielding high solubility and low viscosity.
IMOs and other glucooligosaccharides have long been approved in China and Japan. In Japan, IMOs have been on the list of Foods for Specified Health Use (FOSHU) for more than 10 years. In 2002, over 50% of the FOSHU foods in Japan incorporated oligosaccharides as the functional component. The list includes soft drinks and other beverages, frozen yogurt, confectionery products, sweeteners, cookies, coffee drink mixes, bread, tofu, chocolate, and soup mixes.
The dietary presence of glucooligosaccharides, particularly in the form of IMOs, is intimately tied to the history of fermented foods in East Asia. Fermentation products such as soy sauce (shoyu), soybean-barley paste (miso), sake, and natto are produced by traditional methods exploiting mixed cultures of lactic acid bacteria, acetic acid bacteria, sake yeast, koji molds, and natto bacteria. The filamentous fungus Aspergillus oryzae has been used in the production of traditional fermented foods such as shoyu and miso and drinks such as sake for more than 1,000 years in Japan.
IMOs are considered prebiotics found in several traditional foods such as rice miso, soybean sauce, and sake. Although early consumers of these foods were entirely unaware of GlcOS as discrete chemical entities, regular dietary exposure to low concentrations of these oligosaccharides through fermented staple foods was a feature of traditional East Asian diets over many centuries.
IMOs have been commercially available for decades in Japan, but only recently were IMO products launched for the US, European, and Canadian markets. In Japan, their industrial production and intentional use as a functional food ingredient began in earnest in the late 20th century. The numbers of IMOs-related patent classifications for food, foodstuff, ingredient, medical, and veterinary purposes have steadily increased over the past 26 years.
It is important to distinguish between the incidental presence of trace GlcOS in fermented foods (a feature of traditional diets) and the deliberate, concentrated supplemental use of manufactured GlcOS preparations, which is a modern commercial phenomenon. Because of the high market demand for products containing IMOs, obtaining a sufficient supply of naturally occurring IMOs for commercial use is not economically feasible. Consequently, IMOs are commercially produced through the enzymatic modification of starch. There is no documented history of traditional medicine employing isolated or concentrated GlcOS preparations; the traditional context is dietary rather than therapeutic.
The biological activity of any given GlcOS preparation is highly contingent on its precise structural characteristics. The prebiotic effects (non-digestibility, selective fermentability, and potential health effects) of GlcOS are highly variable due to their complex structure originating from different synthesis processes, and the relationship between GlcOS structure and their potential prebiotic effects has not been fully understood. Key structural variables include:
There is a major concern in classifying IMOs as prebiotics because of their digestibility in the gastrointestinal tract, and only IMOs with high degrees of polymerization — for instance, isomaltotetraose and larger oligomers — are considered indigestible. Conversely, cello-oligosaccharides with β-(1→4) glycosidic bonds are non-fermentable in the human gut and therefore do not qualify as prebiotics for humans.
The predominant route to commercial GlcOS is enzymatic. The most common enzymatic method of IMO production involves α- and β-amylases, (neo)pullulanase, and α-glucosidase acting in concert on starch. The α-glucosidase transfers glucosyl residues and mainly forms α-(1→6) linkages, thus yielding a mixture of glucooligosaccharides containing both α-(1→6) and α-(1→4) glycosidic bonds.
An alternative route uses glucansucrases (glucosyltransferases) produced by lactic acid bacteria. The enzymatic synthesis of oligosaccharides containing only α-d-glucopyranosyl units can be obtained using a subgroup of α-transglucosidases named glucansucrases (EC 2.4.1), which use sucrose as d-glucosyl moiety donor. Glucansucrases classified into the glycoside-hydrolase (GH) family 70 are mostly produced by lactic acid bacteria: Leuconostoc sp., Streptococcus sp., Lactococcus sp., Lactobacillus sp., and Weissella sp. The energy of the osidic bond of sucrose enables the efficient transfer of a d-glucosyl residue via a covalent glycosyl-enzyme intermediate. In addition to high-molecular-weight homopolysaccharides, glycansucrases generally catalyze the synthesis of low-molecular-weight oligosaccharides or glycoconjugates when efficient acceptors, like maltose, are added to the reaction medium.
Specifically regarding Leuconostoc lactis-derived GlcOS: Leuconostoc lactis CCK940, which exhibits glycosyltransferase activity, produces oligosaccharides using sucrose and maltose as donor and receptor molecules, respectively. The purified oligosaccharides consisted only of glucose. NMR analysis revealed that the CCK-oligosaccharides were composed of 77.6% α-1,6 and 22.4% α-1,4 glycosidic linkages, with a molecular weight of 9.42 × 102 Da.
The foundational mechanism by which non-digestible GlcOS exert health effects is their resistance to hydrolysis by human upper-gastrointestinal enzymes and their subsequent fermentation in the colon. Being non-digestible, functional oligosaccharides escape digestion in the upper gut and move to the colon, where they are fermented to lactate, short-chain fatty acids (SCFAs), and carbon dioxide, hence promoting the growth of prebiotic bacteria mainly bifidobacteria and inhibiting the growth of harmful bacteria, thus imparting several health benefits.
IMOs are partially digested in the human body by brush-border enzymes, including maltase/glucoamylase and isomaltase, while the undigested oligosaccharides get fermented in the large intestines, leading to beneficial gastrointestinal effects and prebiotic properties.
GlcOS are generally non-digestible and have been reported to stimulate the growth and/or activity of certain beneficial bacteria and/or enhance the production of SCFAs, which are considered potential prebiotic properties. The primary SCFAs produced — acetate, propionate, and butyrate — serve as energy substrates for colonocytes (especially butyrate), modulate immune signaling, and influence systemic metabolic homeostasis.
Research on the influence of glycosidic bond configuration on SCFA profiles is ongoing. Using a miniaturized in vitro human colonic batch fermentation model to study isomeric glucose disaccharides, diglucose α(1→1) fermentation led to significantly higher butyrate production (p < 0.01) and lower acetate proportion (p < 0.01) compared with other α-bonded diglucoses. Diglucose β(1→4) also led to significantly higher butyrate production (p < 0.05) and significantly increased proportions of propionate and butyrate. However, there was no significant effect of glycosidic bond configuration on absolute propionate production, and despite some differences in SCFA production among different glucose disaccharides, there was no clear overall relationship between SCFA production and bond configuration, suggesting that other factors may be responsible.
This is the most extensively investigated area for GlcOS. Glucooligosaccharides, along with fructooligosaccharides, xylooligosaccharides, and isomaltooligosaccharides, are classified as exhibiting prebiotic activities; they can be produced enzymatically or found naturally in some plants.
In vitro evidence for bifidogenic activity is substantial. In studies using probiotic strains as the sole carbon source, growth of six probiotic strains — Lactobacillus casei, L. pentosus, L. plantarum, Weissella cibaria, Bifidobacterium animalis, and Saccharomyces cerevisiae — was better when CCK-oligosaccharides (GlcOS) were used as the sole carbon source compared with fructooligosaccharides, which are widely used as prebiotics.
Regarding α-(1→3)-glucooligosaccharides derived from the fungus Laetiporus sulphureus, the obtained GlcOS promoted in vitro growth of selected probiotic Lactobacillus (including L. acidophilus, L. plantarum, L. fermentum, L. casei, L. gallinarum, and L. johnsonii) and Bifidobacterium (B. longum subsp. infantis and B. bifidum) strains, but not the potentially pathogenic Escherichia coli DH5α and Enterococcus faecalis.
In a preclinical (murine) in vivo study, these α-(1→3)-glucooligosaccharides enriched intestinal microbiota with bifidobacteria and lactobacilli substantially, which was correlated with increased production of short-chain fatty acids (SCFAs).
In an in vitro fermentation study with human fecal microbiota, fermentation experiments with probiotic Bifidobacterium bifidum ATCC 29521, Bifidobacterium animalis subsp. lactis DSM 10140, and Limosilactobacillus reuteri ATCC 6475 indicated that chemically synthesized GlcOS can be utilized as a carbon source for bacterial growth, and their promotion effect was overall comparable to commercial prebiotics.
Regarding fermentation patterns across different enterotypes, an in vitro study using 15 human fecal samples found that the substrates tested included isomaltooligosaccharides (IMO), and enrichment of Bifidobacterium was affected by both fecal enterotypes and substrates; increased growth of Bifidobacterium was detected in cultures supplemented with a range of prebiotics including GOS and FOS but not consistently for all IMO preparations.
Evidence strength: For bifidogenic activity, in vitro and animal evidence is consistent and robust across multiple GlcOS subclasses. However, dedicated human randomized controlled trials specifically with GlcOS (as opposed to galactooligosaccharides or fructooligosaccharides) remain limited. The heterogeneity in GlcOS structural composition across studies makes generalizations difficult.
The therapeutic potential of IMOs has been explored in obesity, diabetes mellitus, inflammatory bowel disease (IBD), hyperlipidemia, and constipation. Supplementation with IMO normalizes intestinal microbiota composition, reduces intestinal permeability, enhances short-chain fatty acid (SCFA) production, and strengthens intestinal tight junctions.
Animal studies have found that the combination of IMOs and FOS reduced intestinal inflammation in rats by decreasing the histologic score of colitis and IL-1β levels. Although IMOs and FOS induced specific changes in microbiota, they were not directly correlated with colitis reduction, suggesting that their protective mechanisms may be multifactorial.
Evidence strength: Current evidence for gastrointestinal effects derives predominantly from animal models and mechanistic in vitro studies. Human clinical trial data specific to GlcOS for IBD and constipation endpoints are limited.
High-fat diet (HFD)-induced obesity models have shown that IMOs, administered alone or in combination with other compounds, exhibit potent antiobesity effects. Moreover, IMOs exhibit preventive effects against HFD-induced metabolic dysfunction by modulating gut microbiota and short-chain fatty acid levels.
One clinical study examined IMO-based dietary fiber combined with a hypocaloric high-protein diet. In a preliminary repeated single-arm clinical trial with thirteen metabolically healthy adults with a BMI ≥25, the combination significantly improved body composition by reducing total body weight, BMI, body fat percentage, and fasting plasma glucose. This study was small and non-randomized (single-arm), substantially limiting the interpretation of its results.
Evidence strength: Animal evidence for antiobesity effects is promising. Human clinical evidence is preliminary; the one identified clinical trial lacked randomization and a control arm, rendering it insufficient to draw firm conclusions.
The use of IMOs as low-glycemic dietary fiber ingredients is commercially widespread, but the scientific picture is complex and contested. Previous studies, with different commercial IMOs, are inconsistent and reported mixed results — bifidogenic and no impact on blood glucose/breath hydrogen — suggesting IMOs to be partly digestible and partly fermentable.
A key human cross-over glycemic response study (n = 26, then n = 10) found lack of difference in glycemic response (p = 0.662), with no impact on breath hydrogen (24 h; p = 0.319) and intestinal tolerance, demonstrating that the specific commercial IMO tested (BIOLIGO™ IL5040) was digestible and could be used to replace sugars in product formulations. This is a critical finding suggesting that certain commercial IMO preparations are substantially absorbed in the small intestine — functioning more like a digestible sugar than a prebiotic fiber.
Consistent with that finding, a study on acute insulin and glucose responses found that 20 g IMO elicited elevations of plasma glucose (+2.8 mmol/l) and insulin (+1002 pg/ml) at 30 min. More recently, 25 g IMO raised blood glucose by 2.7 mmol/l and insulin by 17.9 µU/ml at 30 min post-ingestion.
In animal research, in an animal study, IMOs and their co-supplementation with FOS ameliorated type 2 diabetes induced by poloxamer 407 in Wistar rats. Co-supplementation decreased glycemic and lipid dysmetabolism and increased glucagon-like peptide-1 levels and bifidobacteria/lactobacilli populations. Ten percent IMOs alone suppressed the increase in blood glucose in the oral glucose tolerance test and fasting blood glucose at 2, 4, and 6 weeks. However, the mechanism by which IMOs suppress type 2 diabetes development remains unknown. Most studies support the hypothesis that soluble fibers can reduce postprandial glucose by delaying gastric emptying, decreasing the accessibility of digestive enzymes, and slowing intestinal nutrient absorption.
Evidence strength: The data are mixed and preparation-dependent. The evidence that certain commercial IMO products elicit meaningful glycemic and insulinemic responses in humans fundamentally challenges their classification as non-digestible prebiotics. Animal data are promising but do not translate directly. No high-quality, long-term RCTs in humans on glycemic outcomes specific to GlcOS have been identified.
IMOs can alleviate hyperlipidemia, as indicated by the reduced histological colitis scores and improved lipid profiles observed in clinical trials and animal studies. IMOs can modulate immune responses, enhance disease resistance, and improve lipid metabolism and liver and kidney functions. The proposed mechanism involves dietary fiber binding to bile acids in the gut: dietary fiber binds to bile, inhibits reabsorption in the small intestine, and stimulates the synthesis of new bile acids from cholesterol, thereby lowering blood cholesterol.
Evidence strength: Largely derived from animal studies and observational contexts. Human RCT evidence specifically targeting lipid outcomes for GlcOS is limited.
GlcOS derived from β-glucans may resemble their parent β-glucans in modulating immunological activities (e.g., antitumor effects, cholesterol control, and glucose metabolism) possibly through the selective increase in specific bacteria modulating cytokine and antibody production and/or enhanced intestinal SCFA production.
A cell-based (in vitro) study investigated α-(1→3)-glucooligosaccharides' potential interaction with natural killer (NK) cells. The study aimed to verify the usefulness of L. sulphureus (1→3)-α-d-glucooligosaccharides for immunotherapy of colon cancer; the study revealed that the investigated oligosaccharides significantly enhanced the ability of NK-92 cells to eliminate examined colon cancer cells, mostly by an increase in their cytotoxic activity. The most significant effect was observed in LS180 and HT-29 cells exposed to a two-times higher quantity of NK cells activated by 500 µg/mL GOS, wherein NK-92 killing properties increased by 20.5% (p < 0.001) and 24.8% (p < 0.001), respectively.
However, the beneficial impact of (1→3)-α-d-glucooligosaccharides on the anticancer properties of NK-92 suggests their use in colon cancer immunotherapy as adjuvants; however, the obtained data require further investigation and confirmation.
Evidence strength: Preliminary and entirely preclinical (in vitro cell culture). No human data exist for immune modulation by GlcOS. These findings are hypothesis-generating only.
The health benefits associated with prebiotics, which include glucooligosaccharides, comprise improvement in the gastrointestinal microflora, enhanced mineral absorption, stimulation of the immune system, and reduced risk of irritable bowel syndrome and of constipation. The enhanced mineral absorption is thought to be mediated by SCFA-induced reduction in luminal pH, which increases solubility and uptake of divalent minerals such as calcium and magnesium. Direct human clinical evidence specifically for GlcOS in mineral absorption has not been identified in the current literature search.
Dosages in the scientific literature span a wide range depending on the study purpose (prebiotic activity vs. acute glycemic response vs. tolerance assessment) and the specific GlcOS preparation used.
IMOs have been Generally Recognized as Safe (GRAS) by the United States Food and Drug Administration (FDA) since 2016, and accepted as novel food ingredients by numerous jurisdictions including Health Canada (2012), European Food Safety Authority (EFSA) in 2010, and Food Standards Australia New Zealand (FSANZ) in 2017.
Generally, all digestion-resistant oligosaccharides, including IMOs, have adverse side effects when consumed in amounts greater than permissible levels. The maximum permissible dose of IMO is 1.5 g/kg body weight, which is reported as higher than for any other sugar substitute. The US FDA has recommended a maximum consumption of 30 g/day for IMO. Higher dosages (greater than 40 g/day) can cause gastrointestinal symptoms like flatulence, bloating, soft stool, or diarrhea.
A scientifically important concern specific to GlcOS — particularly IMOs — is that many commercially available preparations are substantially digestible in the human small intestine, not non-digestible as commonly claimed. Studies with different commercial IMOs are inconsistent and have reported mixed results, suggesting IMO to be partly digestible and partly fermentable. One crossover study demonstrated a lack of difference in glycemic response (p = 0.662), with no impact on breath hydrogen (24 h; p = 0.319) and intestinal tolerance, demonstrating that a specific commercial IMO product is digestible.
This has regulatory implications: the FDA issued a warning letter in 2019 noting that certain IMO products labeled as dietary fiber did not meet the statutory definition of dietary fiber because of their partial digestibility. Consumers and practitioners should be aware that the prebiotic properties of any specific GlcOS product are heavily preparation-dependent, and claims of non-digestibility must be substantiated for each specific product and DP composition.
Acutely, 20 g IMO elicited elevations of plasma glucose (+2.8 mmol/l) and insulin (+1002 pg/ml) at 30 min in healthy subjects. This is a practically significant finding for individuals with glucose metabolism disorders who may be using IMO-containing products as "low-glycemic" options under the assumption of non-digestibility.
No specific drug–GlcOS interactions have been documented in the peer-reviewed literature identified in this search. However, the mechanism by which GlcOS bind bile acids and potentially slow gastric emptying is relevant: these mechanisms theoretically could modulate absorption rates of co-administered lipophilic drugs. No clinical studies directly addressing such interactions were identified.
Considering the gut microbiome's complexity and the bidirectional relationship between metabolic diseases and gastrointestinal disorders, further well-designed clinical trials and mechanistic studies are required before robust efficacy and interaction profiles can be established for GlcOS.
The prebiotic effects of GlcOS are highly variable due to their complex structure originating from different synthesis processes. The relationship between GlcOS structure and their potential prebiotic effects has not been fully understood. A comprehensive summary of GlcOS knowledge has been lacking, indicating the early-stage nature of this research field.
Key unresolved questions include: (1) which specific GlcOS structures reliably resist digestion in the human small intestine; (2) whether the bifidogenic and SCFA-producing effects observed in vitro and in animal models translate to consistent and clinically meaningful outcomes in human populations; (3) whether GlcOS offer distinct advantages over better-characterized prebiotics (FOS, inulin, galactooligosaccharides) for any specific health outcome; and (4) what the long-term safety profile is for higher daily doses (>30 g/day).
Health conditions that Glucooligosaccharides may help support.
Body systems that Glucooligosaccharides may help support.
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