Prebiotic Type Spotlight: Galactooligosaccharides (GOS)

Each edition of GPA’s Prebiotic Spotlight focuses on a specific prebiotic type to raise awareness around the prebiotic itself, its sources, any notable and/or recent research, and how it is used in the marketplace. In this issue, galactooligosaccharides (GOS) are highlighted.  

Overview 

GOS are recognized as prebiotics that support gut health by promoting the growth of beneficial bacteria and inhibiting harmful pathogens (Yu et al., 2024). Structurally, GOS are complex, non-digestible carbohydrates composed of three or more galactose units linked to a terminal glucose molecule (Yoo et al., 2024). GOS are fermented in the lower part of the gastrointestinal tract, producing short-chain fatty acids and lactic acid, altering the pH of the lumen (Ignatova et al., 2025). Furthermore, GOS are recognized as being structurally similar to human milk oligosaccharides, and confer health benefits such as stimulating beneficial microorganisms, reducing production of toxic substances, improving immune response, and increasing mineral absorption, among others (Yoo et al., 2024). In vitro studies have shown that GOS can prevent the adhesion of pathogenic bacteria to the intestinal epithelium (Zhu et al., 2023). 

Benefit Areas 

In recent years, various studies have described associations between GOS supplementation and health benefits, including: 

• • Maternal prebiotic supplementation containing 9:1 ratio of GOS to fructo-oligosaccharide (FOS) favorably modified both the maternal and developing infant’s gut microbiome (Jones et al., 2024).  

• • Supplementing infants with GOS-containing formula sustained high levels of stool bifidobacteria compared to probiotic-containing formula (Heppner et al., 2024).  

• • Adults with constipation experience an improved number of bowel movements following GOS supplementation, and significantly increased Bifidobacterium and Lactobacillus compared to baseline (Lee et al., 2024). 

• • GOS supplementation tended to reduce negative emotional responses compared to a placebo in healthy children aged 6-14 years (Johnstone & Kadosh, 2025). 

• • Synbiotic supplementation containing GOS lowered fasting blood glucose levels more effectively than probiotic supplementation alone in patients with type 2 diabetes mellitus (T2DM) (Zhang et al., 2025).  

 Sources 

GOS are carbohydrates naturally found in legumes such as lentils and chickpeas, as well as dairy products and certain root vegetables (Ariaee et al., 2024; Babakhani et al., 2025). They can also be produced enzymatically through the transgalactosylation of galactosidases (Yu et al., 2024). The chemical composition of GOS can vary significantly depending on the enzyme source and reaction conditions used in their production (Yu et al., 2024). There are two main types of GOS: α-GOS and β-GOS. α-GOS typically contain between one to four galactose moieties connected with alpha bonds, and function as storage reserves and cryoprotectants in frost-resistant plant organs. In contrast, β-GOS are composed of lactose bound to one to five galactose residues via beta bonds and are commonly found in animal and human breast milk (Ignatova et al., 2025). Due to their well-documented safety, stability, solubility, and neutral taste, β-GOS are widely used as additives in many food products, specifically in infant formulas and functional foods.  

Dose Range 

GOS supplementation has been shown to modulate the gut microbiota at doses of 5.5 g/day, significantly increasing the abundance of both Bifidobacterium and Bacteroides (Babakhani et al., 2025). Other clinical trials have demonstrated significantly improved bowel movements in adults with constipation, and increased Bifidobacterium and Lactobacillus at doses as low as 2 g/day of GOS (Lee et al., 2024). A dose of 5.5 g/day has also been associated with a reduction in negative emotional responses in healthy children (Johnstone & Kadosh, 2025). Currently, GOS are approved by the United States’ Food and Drug Administration for supplementation at a concentration of <7.8 g/L or 11 g/serving for use in term infant formula and selected foods and beverages (Hu et al., 2024). GOS are commonly added to infant formulas at concentrations of 5 g/L, effectively enhancing gut microbiota without adverse effects (Hu et al., 2024). In adults, GOS have been reported to be well tolerated at daily doses ranging from 5 to 20 g (Hu et al., 2024).  

Recent Research 

Research on GOS has gained significant attention in recent years due to their health benefits, particularly as prebiotics. Currently, there are four studies listed on ClinicalTrials.gov that are recruiting participants to investigate GOS in various applications such as their effects on symptoms of irritable bowel syndrome, blood glucose levels in healthy adults, and graft-versus host-disease following allogeneic stem cell transplants (ClinicalTrials.gov, 2025). Moreover, searching “galactooligosaccharides” on PubMed retrieved seven clinical trials published in 2025 to date, covering topics ranging from the effects of GOS-containing synbiotics on infant allergy outcomes following maternal supplementation to the impact of GOS on glycemic control in patients with T2DM (PubMed, 2025).   

A randomized, double-blinded, controlled trial conducted by D. Palmer et al. (2025) assessed whether maternal supplementation with dietary prebiotics reduced the risk of allergic outcomes in infants with hereditary risk. A total of six hundred and fifty-two pregnant women with a first-degree relative with a history of medically diagnosed allergic disease were included in this study. Particiants were allocated to consume either 14.2 g/day of prebiotics (GOS and FOS in the ratio 9:1) or a placebo powder, starting before 21 weeks of gestation and continuing through to 6 months postpartum during lactation. The primary outcome was medically diagnosed infant eczema by one year of age, as well as allergen sensitization, food allergies, and recurrent wheeze in the first year of life. Results demonstrated that there were no significant differences between the prebiotic group and placebo group for medically diagnosed eczema. Overall, the researchers found little evidence that maternal prebiotics supplementation during pregnancy and lactation reduces risk of medically diagnosed infant eczema by one year of age in infants who are at hereditary risk of allergic disease. Future studies should use more personalized approaches, in which genetic predisposition, nutritional status, microbiome profiles, and lifestyle factors are all considered.  

A randomized, double-blind, controlled trial by J. Palmer et al. (2025) assessed the effect of prebiotics on behaviour, gastrointestinal symptoms and downstream effects on parental quality of life. Specifically, thirty-three children with autism (ages 4-10 years) were randomized to consume either 2.4 g/day of GOS, or a placebo for six weeks. Stool samples were collected at baseline and following the intervention, and validated questionnaires were used to measure changes in social and mealtime behaviours, gastrointestinal symptoms, and parental quality of life (pQoL). Supplementation with GOS significantly increased levels of fecal Bifidobacterium from baseline and was well tolerated in children. Subsequent effects on gastrointestinal symptoms and pQoL were only marginally changed. Although there were no significant differences in outcomes between groups, the high rates of compliance, absence of side-effects and marginal effects detected encourage further investigations with larger sample sizes.  

A randomized, double-blinded, placebo-controlled study by Zhang et al. (2025) investigated the combination of Bifidobacterium animalis subsp. Lactis and GOS on glycemic control in patients with T2DM. Specifically, one-hundred and twenty T2DM patients were randomized to either consume 5 x 1010 colony forming units (CFU) of the probiotic containing Bifidobacterium animalis subsp. Lactis, a synbiotic containing 5 x 1010 CFU of the probiotic and 0.9 g of GOS, or a placebo, twice daily for 12 weeks. Fasting blood glucose (FBG), hemoglobin A1C (HbA1C), insulin, homeostatic model assessment of insulin resistance (HOMA-IR), inflammatory indicators, oxidative stress indicators, gastrointestinal hormones, gut microbiota, and bile acids were examined at baseline and following the intervention period. All groups had significant decreases in FBG compared to baseline, however participants in the synbiotic group demonstrated significant decreases in HbA1C, serum insulin, and HOMA-IR, which was not observed in the probiotic or placebo groups. In-group comparisons found that the synbiotic had significantly greater reduction in FBG compared to the placebo, as well as significantly modified inflammation, oxidative stress, gut microbiota, serum bile acids, and GLP-1 levels greater than the probiotic supplement alone. This study demonstrates that the effects of consuming a GOS-containing synbiotic surpass that of consuming probiotics alone by reducing FBG and other outcomes in patients with T2DM, potentially attributable to the enhanced modulation of the gut microbiota.  

How is GOS used in the marketplace? 

According to The Business Research Company (2025), the global GOS market size reached an estimated $850 million USD in 2024 and is expected to reach $930 million USD this year. Longer term projections expect the GOS market to reach $1.33 billion USD in 2029, with a compound annual growth rate (CAGR) of 9.3%. Key market drivers include the rise in premature births and associated health issues. GOS are thought to minimize preterm birth by promoting healthy gut microbiomes and reducing inflammation, which overall may improve pregnancy outcomes. Additionally, GOS are often used in milk-based products and infant formulas to mimic the effects of breast milk oligosaccharides (Yoo et al., 2024). Major companies operating in the GOS market are focusing on advancing the enzymatic synthesis process in GOS production to enhance efficiency, optimize yields, and improve the overall quality of GOS products. GOS are commonly added to infant formulas, dietary supplements, and functional foods to enhance gut health, support the immune system, and improve calcium absorption.