Is Galacto Oligosaccharides Safe?

Galacto-oligosaccharides (GOS) are a mixture of galactose and glucose linked by β (1-3), β (1-4) or β (1-6) bonds, with a degree of polymerization of 2 to 8. Oligosaccharides cannot be directly digested and absorbed by the human body, but are fermented by intestinal microorganisms to produce a series of health effects, such as improving constipation [1], regulating intestinal flora [2], enhancing immunity [3], and promoting mineral absorption [4]. Commercialized oligosaccharide galactose raw materials are mainly obtained by enzymatic preparation, often produced by hydrolyzing milk. The health potential of oligosaccharides as prebiotics is constantly being researched and discovered, and their application as nutritional supplements and food ingredients in the food industry is very popular. This article mainly reviews the safety of oligosaccharides, as well as their effects on intestinal health and immune function in different populations and their possible mechanisms.

2 Safety evaluation of oligosaccharides

Animal experiments and a number of clinical intervention trials have not found any toxicity in the host when using galacto-oligosaccharides in infant foods and conventional foods. Acute toxicity experiments in SD rats showed that 5000 mg/kg of galacto-oligosaccharides had no acute toxicity [5]. In a 90-day repeated oral toxicity experiment in rats, 500, 1000 and 2000 mg/kg of oligosaccharides had no significant effect on any clinical indicators or histopathology [6]. Two multicenter randomized controlled studies showed that there were no negative effects of adding 4 g/L or 8 g/L galacto-oligosaccharides to newborn formula, and that newborns tolerated galacto-oligosaccharides well [7-8]. The no observed adverse effect level (NOAEL) for galacto-oligosaccharides in adult men and women is at least 2 g/(kg·d) [6]. In the United States, oligosaccharides are considered to be generally recognized as safe (GRAS) and safe for all populations. The European Union also recognized oligosaccharides as a safe food component before 1997. In 2007, oligosaccharides were marketed in China as a nutritional enhancer for infant foods and as a novel food source. The recommended intake is ≤ 15 g/d. No studies have been found that suggest that this recommended value is harmful to health.

3 Galacto-oligosaccharides regulate intestinal flora

Twenty of the 21 randomized controlled clinical studies on the effect of galacto-oligosaccharides on the intestinal flora in adults showed that galacto-oligosaccharides can regulate intestinal flora. Supplementation with 5 to 15 g/d of oligosaccharides in adults can increase the number of bifidobacteria and lactobacilli in the intestine, while reducing the levels of harmful bacteria such as Desulfovibrio and the conditionally pathogenic bacterium Salmonella. SCHOEMAKER et al. [1] gave 132 constipated adult women 5. 5 and 11 g/d of oligosaccharides, and after 3 weeks, it was observed that the bifidobacterial abundance in the 11 g/d group increased from 10. 9% to 23. 9%, and the butyric acid-producing bacteria (Anaerostipes hadrus) also showed an increasing trend.

The dose of oligosaccharides was increased to 10 to 15 g/d or 15 to 20 g/d, which also showed an increase in the number of bifidobacteria, but the relative abundance of lactobacilli in the low-dose group increased significantly [9]. In addition, oligosaccharides also exhibit a bacteriostatic effect. A randomized controlled study conducted in the UK found that the abundance of Bifidobacterium in 64 healthy women increased by 11.5% after 4 weeks of intervention with 5.5 g/d oligosaccharides, accompanied by a decrease in the number of Desulfovibrio species [10]. However, a low dose of 1.4 g/d oligosaccharide intervention in 69 British people did not observe the effect of regulating the intestinal flora [11]. In summary, 5 to 15 g/d oligosaccharides can regulate the intestinal flora in adults and have a positive effect on human intestinal health.

Five randomized controlled clinical studies on the effect of galacto-oligosaccharides on the intestinal flora of the elderly were included, and they also showed that galacto-oligosaccharides can regulate the intestinal flora. The effect of galacto-oligosaccharides on the intestinal flora of the elderly is similar to that in adults, and it can promote an increase in bifidobacteria and inhibit the growth of harmful bacteria such as Escherichia coli and Vibrio desulfurans. The intestinal function of the elderly weakens, and the composition of the intestinal microflora may potentially change with age. For example, with age, the level of bifidobacteria in the intestine and the number of butyrate-producing bacteria Clostridium cluster XIVa decrease [12]. As a prebiotic, oligosaccharides can regulate the ecology of the aging intestine and promote the positive development of the flora and the environment. WILMS et al. [3] used 15 g/d oligosaccharides for 4 weeks to intervene, and the bifidobacterial count of 20 elderly people and 24 healthy adults increased. The elderly people with the lowest basal bifidobacterial levels had a greater increase. After stopping the oligosaccharide intervention, the abundance of the flora returned to baseline levels without any residual effects. galactose intervention, the abundance of the flora returned to baseline levels, with no residual effects. At the same time, the elderly's intestinal Escherichia coli and Vibrio desulfurans were inhibited by oligosaccharides, suggesting that oligosaccharides can inhibit the growth of harmful bacteria.

Eleven randomized controlled clinical studies on the effect of oligosaccharides on the intestinal flora of infants and young children were included. Ten of them showed that oligosaccharides can significantly increase the content of bifidobacteria in the intestines of infants and young children. The literature shows that the dosage of galacto-oligosaccharides consumed by infants and young children increases with age. The dosage of galacto-oligosaccharides consumed by infants and young children increases with age.

The dosage of galacto-oligosaccharides consumed by infants and young children increases with age. The dosage of galacto-oligosaccharides consumed by infants and young children increases with age. The dosage of galacto-oligosaccharides consumed by infants and young children increases with age. The dosage of galacto-oligosaccharides consumed by infants and young children increases with age. The dosage of galacto-oligosaccharides consumed by infants and young children increases with age. The dosage of galacto-oligosaccharides consumed by infants and young children increases with age. The dosage of galacto-oligosaccharides consumed by infants and young children increases with age. The dosage of galacto-oligosaccharides consumed by infants and young children increases with age.

The dosage of galacto-oligosaccharides consumed by infants and young children increases with age. The dosage of gal BEN et al. [13] found that 0.3 g/L oligosaccharide-enriched formula milk significantly increased the abundance of Bifidobacterium in full-term newborns. FANARO et al. [14] found that formula milk containing 5 g/L oligosaccharides had a bifidogenic effect in infants aged 4 to 6 months, and that Lactobacillus tended to increase . In addition, PAGANINI et al. [15] observed that formula milk containing 7.5 g/L galacto-oligosaccharides for infants aged 6.5 to 9.5 months also had the above-mentioned effect of regulating the intestinal flora, and also inhibited the growth of pathogenic bacteria such as Escherichia coli and Salmonella. However, BEN et al. [13] did not observe changes in the intestinal flora of newborns when using formula milk containing 0.24 g/L oligosaccharides. In summary, oligosaccharide intake in the range of 0.3 to 7.5 g/L can regulate the balance of the intestinal flora in infants from birth to 6 months of age.

In vitro and in vivo experiments have found that oligosaccharides have a beneficial effect on the intestinal flora, as they can increase the number of bifidobacteria and lactobacilli and inhibit the growth of pathogenic bacteria such as Shigella dysenteriae, Proteus mirabilis and Citrobacter rodentium. In vitro fermentation experiments have shown that the bifidogenic effect of oligosaccharides is dose-dependent, with high concentrations of oligosaccharides significantly increasing the number of bifidobacteria [16]. Animal experiments have found that oligosaccharides inhibit the abundance of Proteobacteria phylum and Escherichia Shigella genus in the intestines of mice with intestinal barrier damage induced by lipopolysaccharide (LPS), while increasing the proliferation of Akkermansia Lactobacillus and Bifidobacterium proliferate in the intestine [17].

Galacto-oligosaccharides are structurally similar to the epithelial cell sites recognized by intestinal pathogens and competitively inhibit bacterial adhesion, thereby preventing colonization and growth of pathogens [18]. In vitro experiments have shown that purified galacto-oligosaccharides inhibit the adhesion of the human epithelioma-2 (HEp-2) and human colorectal adenocarcinoma cells (Caco-2), and reduce the adhesion of the enteropathogenic E. coli (EPEC) by 65% and 70% respectively [19]. adhesion by 65% and 70% respectively [19]. In another experiment, galacto-oligosaccharides reduced the adhesion of the pathogen Citrobacter rodentium to intestinal epithelial cells, and this effect was dose-dependent [20].

4 Galacto-oligosaccharides modulate immune function

Nine randomized controlled clinical studies on the effect of galacto-oligosaccharides on immune function in adults were included. Five studies showed that galacto-oligosaccharide intake of 5 g/d or more in adults can improve the body's immune level by regulating mucosal immunity and a combination of inflammatory factors. MOREL et al. [21] investigated the effect of 6, 12, and 18 g/d α-lactose oligosaccharides on inflammatory markers such as lipopolysaccharides in a Chinese population. After 15 days, the plasma lipopolysaccharide levels decreased dose-dependently, and the C-reactive protein was significantly lower than in the control group. group. In another overweight and obese population, 5.5 g/d of oligosaccharides was given, and an increase in fecal secretory IgA was observed after 12 weeks, indicating that oligosaccharide intake is involved in the maintenance of the intestinal barrier. The concentration of plasma C-reactive protein did not change significantly at 6 weeks of intervention, but was significantly lower at 12 weeks, lowered, suggesting that it may take longer for oligosaccharides to exert their effects in the human body [22]. 427 American university students received 2.5 and 5.0 g/d oligosaccharide interventions, and compared with the control group, their influenza symptoms and days were reduced [23]. Oligosaccharides seem to resist influenza attacks by enhancing overall immunity, but there are subjective factors in the definition of the number of flu days and the determination of flu patients in this study.

Two randomized controlled clinical studies on the effect of galacto-oligosaccharides on immune function in the elderly were included. The effect of galacto-oligosaccharides in regulating inflammatory factors can be observed in the elderly population. A study of 40 elderly British people who were given a 5.5 g/d oligosaccharide intervention for 10 weeks observed an increase in the plasma concentration of the inflammatory factor interleukin-10 (IL-10), an increase in natural killer cell (NK) activity, and a decrease in IL-1β [24]. activity increased and IL-1β decreased [24]. Another study in the elderly population showed that 5.5 g/d of galacto-oligosaccharides had the same effect as described above, and that phagocytic function was enhanced with longer intervention periods [25]. Since the level of inflammation is higher in the elderly, it is easier to observe the effect of galacto-oligosaccharide intake on changes in the level of inflammatory factors in the body.

Three randomized controlled clinical studies on the effect of galacto-oligosaccharides on the immune function of infants and children were included. Changes in blood biochemical parameters were found in children supplemented with galacto-oligosaccharides. Treatment of children with acute malnutrition with 4. 1 to 6. 1 g/L or 5. 5 to 8. 25 g/L oligosaccharides significantly reduced the erythrocyte sedimentation rate, and the number of vomiting episodes per day decreased significantly with increasing intake [26]. An increase in the erythrocyte sedimentation rate is thought to increase the chance of infection. 365 healthy full-term infants under the age of 8 weeks  healthy term infants fed formula containing 0.44–0.5 g/L galacto-oligosaccharides showed no effect on IgA and allergies [27]. It seems that galacto-oligosaccharides cannot directly increase antibody levels and influence allergic reactions in infants and young children. Immunologically relevant positive effects can also be observed when galacto-oligosaccharides are combined with other prebiotics or probiotics.

SCHOLTENS et al. [28] found that the sIgA concentration (719 μg/g) in the infant formula group containing 6 g/L of short-chain galacto-oligosaccharides and long-chain fructo-oligosaccharides (scGOS/lcFOS) was higher than that in the control group (263 μg/g), suggesting a positive effect on mucosal immunity a positive effect. RANUCCI et al. [29] investigated the effect of galacto-oligosaccharide/glucan (GOS/PDX) on atopic dermatitis and respiratory tract infections in 400 infants. The results showed that the incidence of recurrent respiratory tract infections and asthmatic lower respiratory tract infections in the intervention group was lower than that in the control group.

In vitro experiments have found that galacto-oligosaccharides can directly or indirectly regulate mucosal immunity, immune cell activity and the level of inflammatory factors, thereby participating in the body's immune process. Firstly, it maintains the integrity of the intestinal mucosal barrier through the secretion of signal factors, and participates in mucosal immunity. Galacto-oligosaccharides can drive helper T cells Th1 by enhancing the secretion of galectin-9 by intestinal epithelial cells [30]. Galectin-9 can upregulate the secretion of cytokines such as interferon gamma (IFN-γ) and IL-10, and downregulate the secretion of IL-13 and tumor secretion of tumor necrosis factor-α (TNF-α) to support mucosal immunity [31]. In addition, oligosaccharides can promote the significant upregulation of mucin secretion genes MUC2, TFF3 and RETNLB mRNA expression, regulate intestinal epithelial cell apoptosis [32-33], thereby maintaining the stability of intestinal epithelial structure and function and ensuring normal mucosal immunity .

Second, it activates immune cells and promotes the production of immune proteins. In one study, galacto-oligosaccharides interacted with T cells and dendritic cells, and selectively promoted the induction of regulatory T cells (Tregs) to release IL-10 in vitro [34]. Galacto-oligosaccharides also stimulate the secretion of the intestinal immune protein sIgA, which, together with mucins, forms a biochemical and immunological barrier against exogenous toxins [17]. Third, they regulate cytokine secretion. In vivo studies have found that oligosaccharides reduce the amount of inflammatory factors IL-1β and IL-6 secreted by immune cells such as mononuclear macrophages and inhibit the phosphorylation of the TLR4/NFκB signal, thereby inhibiting the inflammatory response [17]. In summary, galacto-oligosaccharides can directly or indirectly activate immune cells and inhibit the release of inflammatory factors to reduce intestinal inflammatory responses, thereby participating in immune regulation.

Furthermore, most studies have found that the intake of galacto-oligosaccharides is accompanied by an increase in the number of bifidobacteria in the intestine. Bifidobacteria are considered probiotics that enhance the immune function of the body, and they can inhibit the proliferation of pathogenic bacteria in the intestine [35]. Bifidobacteria are the dominant intestinal flora in early life, stimulated by the components of breast milk, producing aromatic lactic acid, which is further involved in intestinal homeostasis and immune regulation in infants [36]. Therefore, in addition to directly acting on the body's immunity, the bifidogenic effect of galacto-oligosaccharides can indirectly participate in immune regulation and maintain a healthy state.

5 Galacto-oligosaccharides relieve intestinal symptoms

Nine randomized controlled clinical studies on the effect of oligosaccharides on relieving intestinal symptoms in adults were included. Eight of the included studies showed that oligosaccharides relieved constipation symptoms or abdominal pain in adults. Low doses of 1.4-3.5 g/d oligosaccharides relieved irritable bowel syndrome (IBS) patients with abdominal pain and bloating symptoms and improves stool shape. Low galactose intake of 3.5 g/d or more may relieve symptoms in constipation patients. WILSON et al. [11] in irritable bowel syndrome patients on a low fermentable oligosaccharides, disaccharides, monosaccharides and polyols (FODMAP) diet (low FODMAP diet, LFD) supplemented with 1.4 g/d of galacto-oligosaccharides, compared with a pure LFD diet and the control group, abdominal pain, loose stools and diarrhea symptoms were relieved by 67%. However, low-dose oligosaccharides failed to increase the levels of bifidobacteria and short-chain fatty acids in the intestine caused by the LFD diet, and there was no effect on stool consistency and frequency.

Increasing the dose of galacto-oligosaccharides to 3.5 g/d was found to increase the consistency of the stool in patients with irritable bowel syndrome, and the bowel movement score also improved to a certain extent. There were a total of three studies on female constipation or subjects with a large proportion of women. The study found that women over 35 years old are prone to constipation, possibly because the transit time of the colon in middle-aged women is significantly slower than that of younger women. 5. 5 g/d low-molecular-weight galactose was used to treat constipated women. The patients reported an increase in stool frequency and a roughly threefold increase in intestinal comfort scores [1]. It is inferred that oligosaccharide intake can improve bowel frequency, and it is recommended that women can moderately increase oligosaccharide intake to improve constipation symptoms.

Three randomized controlled clinical studies on the effect of oligosaccharides on bowel symptoms in the elderly were included, and two showed that oligosaccharides relieved bowel symptoms in the elderly. In an elderly constipation population with a mean age of 76 years, the use of 12 g/d of oligosaccharides resulted in a significant increase in the number of bowel movements after 3 weeks, easier bowel movements, and a significant reduction in constipation symptoms [37]. The use of 10 g/d of oligosaccharides in the elderly had similar results. In a Finnish study on constipation in the elderly, it was found that after 2 weeks of consuming 9 g/d of galacto-oligosaccharides, there was a slight improvement in bowel frequency and stool consistency, but the difference was not statistically significant, which may be related to the small sample size (7 people in each group). [38] In summary, the higher dose of galacto-oligosaccharides used in constipated elderly people may be expected to increase the level of beneficial intestinal bacteria while relieving intestinal symptoms, thereby promoting intestinal function and physical health in the elderly.

Ten randomized controlled clinical studies on the effect of galacto-oligosaccharides on intestinal symptoms in infants and young children were included. Eight studies showed that intestinal symptoms such as abdominal pain, flatulence, and stool characteristics in infants and young children could be improved. When the dose of galacto-oligosaccharides supplement for infants and young children is 1.7-5 g/L, the stool moisture increases, the stool is softer, but the frequency of defecation does not increase. 160 infants were divided into groups according to the frequency of defecation, and the α1-3, β1-4, and α1-3 galactose contents of breast milk were measured. The oligosaccharide content was highest in the group with the highest frequency of defecation, and decreased in the other groups in turn. It was speculated that the low oligosaccharide content in breast milk was related to the reduced frequency of defecation in infants aged 0–6 months [39]. decrease [39]. Subsequently, GIOVANNINI et al. [7] found that 4 g/L oligosaccharides can normalize or soften the stools of 89% full-term infants, and the incidence of abdominal cramps is reduced. In summary, the addition of oligosaccharides to infant formula within a safe dose can effectively relieve constipation symptoms.

In vitro and in vivo experiments have found that galacto-oligosaccharides can indirectly improve intestinal symptoms by adjusting the intestinal environment. Galacto-oligosaccharides can lower the pH of the intestine, and this acidic environment helps the production of butyric and propionic acids, which are metabolites of intestinal flora. Short-chain fatty acids can regulate the expression and distribution of tight junction proteins in intestinal epithelium, maintain goblet cell clusters and mucus production, thereby maintaining the integrity of the intestinal barrier [40-41].

The integrity of the intestinal structure provides a basis for the balance of water and electrolytes and other metabolism, and the low acidity also provides a good living environment for the intestinal flora. Therefore, oligosaccharides can cause changes in the intestinal environment, which can improve intestinal symptoms caused by diseases, especially the characteristics of feces. In constipated rats, the water content of feces and intestinal transport rate were significantly higher after treatment with oligosaccharides than in the control group, and constipation symptoms were effectively relieved. At the same time, the number of intestinal epithelial cells increased [42]. Many animal experiments have found that the level of short-chain fatty acids in the intestine increases after intervention with oligosaccharides. However, the specific mechanism is not yet clear. As the symptoms ease, the abundance of bifidobacteria in the intestinal flora also changes.

6 Other

In addition to the above health effects, galacto-oligosaccharides also have a positive effect on regulating blood sugar and blood lipids, promoting iron absorption in women, and skin care. A double-blind crossover trial in the UK found that galacto-oligosaccharides can lower total blood cholesterol and low-density lipoprotein cholesterol levels, as well as suppress postprandial blood glucose levels. In a 12-week study, obese people aged 18 to 65 without type 2 diabetes who consumed 5.5 g of T-fructooligosaccharides per day had significantly lower levels of total cholesterol, triglycerides and insulin in their blood plasma [22].

In addition, galacto-oligosaccharides can be used as a supplement to iron supplements to enhance the absorption of iron in women. Four studies have shown that women taking 15 g/d of galacto-oligosaccharides in combination with the iron supplement ferrous fumarate (FeFum) have improved iron bioavailability and permeability [43]. Galacto-oligosaccharides can reduce skin water loss, inhibit melanin production and reduce the formation of wrinkles [44].

7 Conclusion

Current results from human intervention studies show that galacto-oligosaccharides can increase the number of lactobacilli and bifidobacteria, inhibit the growth of harmful bacteria, and maintain the balance of intestinal flora. Galacto-oligosaccharides can promote the immune function of the body, and the mechanism may be achieved by increasing the number of beneficial intestinal bacteria, maintaining intestinal barrier homeostasis, regulating the function of immune cells, and inhibiting the secretion of inflammatory factors. In addition, galacto-oligosaccharides can effectively relieve abdominal symptoms and improve constipation symptoms in a dose-dependent manner. The various health benefits of oligosaccharides have been confirmed in human studies, and they are prebiotics with a high level of evidence. However, some mechanisms are still unclear and require support from more population data, especially evidence from the Chinese population, to further verify the health benefits of oligosaccharides.

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