**4. Health impacts of prebiotics**

Stimulating the growth of beneficial bacteria with prebiotics can lead to a cascade of health effects, as illustrated in **Figure 8**. Much of the historical focus had been on *Bifidobacterium spp*. and *Lactobacillus spp.*, although more recently, beneficial health outcomes have been associated with other microbial species as well. Short chain fatty acids, primarily acetate, propionate, and butyrate, along with lactate, are produced by fermentation of non-digestible fibers and prebiotics, potentially reducing the pH within the colon. This can promote absorption of minerals such as

**Figure 8.** *Health impacts associated with prebiotic intake.*

calcium, and limit growth of yeasts, potentially pathogenic bacteria, and microbes responsible for protein fermentation [3]. The extent of such a pH reduction *in vivo* is difficult to establish, however, given that greater than 90% of SCFAs are typically absorbed, and as little as 5% may be excreted [33]. Thus, changes in fecal SCFA levels (or pH) may be difficult to detect, or may not represent what is present in the digestive tract. Autopsy samples indicate SCFA levels are an order of magnitude greater in the cecum than the ileum, and that levels decrease from about 70–140 mM in the proximal colon to 20–70 mM in the distal colon [33].

The effect of increased colonic SCFA production may, however, be observed in the form of distal health impacts mediated by the SCFAs that have been absorbed into the bloodstream. Each SCFA has a different effect on host metabolism, yet the direct effect of a prebiotic on SCFAs can be difficult to establish, due to crossfeeding between microbes that directly consume the prebiotic and other microbes within the digestive tract. Dietary fiber intake also affects SCFAs, further clouding interpretation of fecal SCFA levels. The impacts of prebiotics on SCFA levels are easier to detect via *in vitro* cultures, particularly monocultures, and in gut simulators that contain mixed microbial communities that enable cross-feeding, such as acetate production via one class of microbes, and acetate conversion into butyrate by, e.g., *E. rectale, F. prausnitzii,* or *Roseburia* spp. [3].

SCFAs provide energy for colonocytes, and, after absorption into the portal vein, are metabolized by the liver, modulating cholesterol synthesis, maintaining glucose homeostasis in peripheral tissues, and producing long chain fatty acids. SCFAs can act on leukocytes that modulate immune responses, beneficially impact hormones that influence satiety, and influence neural signals that modulate appetite and food intake via the gut-brain axis [3]. Acetate can influence hormones responsible

**63**

tration of 15 g/d FOS [53].

*Functional Attributes and Health Benefits of Novel Prebiotic Oligosaccharides Derived…*

liver, and to a lesser extent, in the muscle, kidney, heart, and brain [3].

clinical trial results from these novel prebiotic oligosaccharides.

statistically significant reduction in blood glucose and HbA1C.

et al. [45] with AXOS, and Lecerf et al. [38] with XOS.

for cholesterol production, and may be transported to the muscle and the brain; acetate may thus contribute to effects attributed to the "Gut-Brain Axis". Propionate can play a role in hepatic regulation of glucose and synthesis of cholesterol, while butyrate can promote growth of protective colonocytes via colonic epithelial cells. Consequently, microbes fed directly or indirectly by prebiotics can influence health via SCFAs that act either locally within the digestive tract, or distally, mainly via the

As noted previously, XOS and AXOS are oligomers of 5-carbon sugars, connected by β-1,4 bonds. Fewer types of microbes contain the enzymes and transport systems necessary to utilize XOS and AXOS, thus conferring greater selectivity to beneficial bacteria (see **Figures 5** and **6**). Mannooligosaccharides (MOS), although based upon a 6-carbon sugar backbone, are connected via β-1,4 bonds that also render them less susceptible to microbial utilization. In this section, we summarize

**Tables 3** and **4** summarize clinical trial results with XOS and AXOS, respectively, outlining impacts on the microbiome and various clinical biomarkers. Clinical trials with XOS were conducted with doses ranging from 0.4 to 8 g per day; most were in the range from 1 to 3 g per day. A statistically significant increase in *Bifidobacteria* was observed in most trials with XOS [34–39]. Improvements in laxation were noted by Childs et al. [34], Chung et al. [35], Iino et al. [40], and Tateyama et al. [41]; the latter was a study in constipated pregnant women. Studies by Childs et al. [34], Na and Kim [39], and Sheu et al. [42] observed improvements in triglyceride and cholesterol levels, at doses as low as 2.8 g/d, whereas Yang et al. [43] did not observe changes in triglycerides when dosing XOS at 2 g/d (2.8 g/d of a 70% purity product). Yang et al. [43] observed a tendency towards a reduction in OGTT insulin in prediabetes patients dosed with 2.8 g/d of 70% XOS, but no effect on blood glucose, unlike Na and Kim [39], who noted a reduction in blood glucose at a XOS dose of 2.8 g/day. Sheu et al. [42], in a trial with diabetic patients receiving 4 g/d of XOS, observed a

Studies with AXOS complement studies with XOS, since most AXOS products are comprised of at least ~50% XOS. All studies noted an increase in *Bifidobacteria* [44–48]. Francois et al. [45] and Walton et al. [48] observed increased fecal levels of SCFAs (acetate, propionate, and butyrate). Reductions in cresol, indicative of reduced protein fermentation, were observed by Cloetens et al. [44] and Francois

The bifidogenic effect and health benefits observed in the various clinical trials with XOS and AXOS where generally observed at a dose less than 4 g/d. By comparison, approximately 10–20 g/d of FOS is needed to trigger a bifidogenic effect, and the required inulin dose is stated to be at least 15 g/d [49, 50]. Alfa et al. [51] required a dose of 30 g/d of resistant starch to enhance *Bifidobacterium* levels.

Miremadi et al. [52] summarized clinical trials in which various prebiotics were evaluated to assess cardiovascular impacts, particularly reductions in cholesterol, lipids and blood pressure. No improvements to lipid profile were observed with 5.5 g of GOS or 20 g/d of FOS (type not specified), whereas triglyceride levels improved following consumption of 10 and 20 g/d of inulin. Similarly, Alles et al. were unable to detect changes in blood glucose and lipid profiles following adminis-

The higher doses required for a bifidogenic effect or clinical efficacy compared

to XOS and AXOS is likely due to the greater selectivity of XOS and AXOS for beneficial bacteria, versus the widespread utilization of FOS and GOS [11, 23, 31].

*DOI: http://dx.doi.org/10.5772/intechopen.89484*

**4.1 XOS/AXOS**

*Functional Attributes and Health Benefits of Novel Prebiotic Oligosaccharides Derived… DOI: http://dx.doi.org/10.5772/intechopen.89484*

for cholesterol production, and may be transported to the muscle and the brain; acetate may thus contribute to effects attributed to the "Gut-Brain Axis". Propionate can play a role in hepatic regulation of glucose and synthesis of cholesterol, while butyrate can promote growth of protective colonocytes via colonic epithelial cells. Consequently, microbes fed directly or indirectly by prebiotics can influence health via SCFAs that act either locally within the digestive tract, or distally, mainly via the liver, and to a lesser extent, in the muscle, kidney, heart, and brain [3].

## **4.1 XOS/AXOS**

*Prebiotics and Probiotics - Potential Benefits in Nutrition and Health*

calcium, and limit growth of yeasts, potentially pathogenic bacteria, and microbes responsible for protein fermentation [3]. The extent of such a pH reduction *in vivo* is difficult to establish, however, given that greater than 90% of SCFAs are typically absorbed, and as little as 5% may be excreted [33]. Thus, changes in fecal SCFA levels (or pH) may be difficult to detect, or may not represent what is present in the digestive tract. Autopsy samples indicate SCFA levels are an order of magnitude greater in the cecum than the ileum, and that levels decrease from about 70–140 mM

The effect of increased colonic SCFA production may, however, be observed in the form of distal health impacts mediated by the SCFAs that have been absorbed into the bloodstream. Each SCFA has a different effect on host metabolism, yet the direct effect of a prebiotic on SCFAs can be difficult to establish, due to crossfeeding between microbes that directly consume the prebiotic and other microbes within the digestive tract. Dietary fiber intake also affects SCFAs, further clouding interpretation of fecal SCFA levels. The impacts of prebiotics on SCFA levels are easier to detect via *in vitro* cultures, particularly monocultures, and in gut simulators that contain mixed microbial communities that enable cross-feeding, such as acetate production via one class of microbes, and acetate conversion into butyrate by, e.g.,

SCFAs provide energy for colonocytes, and, after absorption into the portal vein, are metabolized by the liver, modulating cholesterol synthesis, maintaining glucose homeostasis in peripheral tissues, and producing long chain fatty acids. SCFAs can act on leukocytes that modulate immune responses, beneficially impact hormones that influence satiety, and influence neural signals that modulate appetite and food intake via the gut-brain axis [3]. Acetate can influence hormones responsible

in the proximal colon to 20–70 mM in the distal colon [33].

*E. rectale, F. prausnitzii,* or *Roseburia* spp. [3].

**62**

**Figure 8.**

*Health impacts associated with prebiotic intake.*

As noted previously, XOS and AXOS are oligomers of 5-carbon sugars, connected by β-1,4 bonds. Fewer types of microbes contain the enzymes and transport systems necessary to utilize XOS and AXOS, thus conferring greater selectivity to beneficial bacteria (see **Figures 5** and **6**). Mannooligosaccharides (MOS), although based upon a 6-carbon sugar backbone, are connected via β-1,4 bonds that also render them less susceptible to microbial utilization. In this section, we summarize clinical trial results from these novel prebiotic oligosaccharides.

**Tables 3** and **4** summarize clinical trial results with XOS and AXOS, respectively, outlining impacts on the microbiome and various clinical biomarkers. Clinical trials with XOS were conducted with doses ranging from 0.4 to 8 g per day; most were in the range from 1 to 3 g per day. A statistically significant increase in *Bifidobacteria* was observed in most trials with XOS [34–39]. Improvements in laxation were noted by Childs et al. [34], Chung et al. [35], Iino et al. [40], and Tateyama et al. [41]; the latter was a study in constipated pregnant women. Studies by Childs et al. [34], Na and Kim [39], and Sheu et al. [42] observed improvements in triglyceride and cholesterol levels, at doses as low as 2.8 g/d, whereas Yang et al. [43] did not observe changes in triglycerides when dosing XOS at 2 g/d (2.8 g/d of a 70% purity product). Yang et al. [43] observed a tendency towards a reduction in OGTT insulin in prediabetes patients dosed with 2.8 g/d of 70% XOS, but no effect on blood glucose, unlike Na and Kim [39], who noted a reduction in blood glucose at a XOS dose of 2.8 g/day. Sheu et al. [42], in a trial with diabetic patients receiving 4 g/d of XOS, observed a statistically significant reduction in blood glucose and HbA1C.

Studies with AXOS complement studies with XOS, since most AXOS products are comprised of at least ~50% XOS. All studies noted an increase in *Bifidobacteria* [44–48]. Francois et al. [45] and Walton et al. [48] observed increased fecal levels of SCFAs (acetate, propionate, and butyrate). Reductions in cresol, indicative of reduced protein fermentation, were observed by Cloetens et al. [44] and Francois et al. [45] with AXOS, and Lecerf et al. [38] with XOS.

The bifidogenic effect and health benefits observed in the various clinical trials with XOS and AXOS where generally observed at a dose less than 4 g/d. By comparison, approximately 10–20 g/d of FOS is needed to trigger a bifidogenic effect, and the required inulin dose is stated to be at least 15 g/d [49, 50]. Alfa et al. [51] required a dose of 30 g/d of resistant starch to enhance *Bifidobacterium* levels.

Miremadi et al. [52] summarized clinical trials in which various prebiotics were evaluated to assess cardiovascular impacts, particularly reductions in cholesterol, lipids and blood pressure. No improvements to lipid profile were observed with 5.5 g of GOS or 20 g/d of FOS (type not specified), whereas triglyceride levels improved following consumption of 10 and 20 g/d of inulin. Similarly, Alles et al. were unable to detect changes in blood glucose and lipid profiles following administration of 15 g/d FOS [53].

The higher doses required for a bifidogenic effect or clinical efficacy compared to XOS and AXOS is likely due to the greater selectivity of XOS and AXOS for beneficial bacteria, versus the widespread utilization of FOS and GOS [11, 23, 31].


#### **Table 3.**

*Summary of clinical trials with XOS.*

For example, Mao et al. [23] found that 237 out of 453 strains (114 genera) of gut bacteria contained the necessary transporters and enzymes for some type/degree of FOS utilization, suggesting fairly widespread utilization of FOS, which will impact the effective dose required to grow the targeted beneficial bacteria. Similarly, Goh et al. [11] note the widespread ability of microbes to utilize lactose, suggesting the presence of LacS (or similar) transporters and enzymes in many microbes that

**65**

benefits.

**Table 4.**

*Summary of clinical trials with AXOS.*

**4.2 MOS**

*Functional Attributes and Health Benefits of Novel Prebiotic Oligosaccharides Derived…*

would allow use of the GGan type of GOS. This is consistent with the observations of Makelainen et al. [31], who also observed excellent growth of many species, beneficial and pathogenic, on GOS (see also **Figure 4**). Ultimately, increased sharing of prebiotic substrates among bacteria means that a higher dose is needed to trigger sufficient growth of the targeted beneficial bacteria that produce the desired health

Manno-oligosaccharides (MOS), extracted from yeast cell walls, coffee or biomass rich in mannan, are typically comprised of up to 6 mannose subunits connected by β-1,4 bonds. MOS have not been as extensively evaluated in humans, but

Salinardi et al. [54] observed a reduction in body volume and adipose tissue in men consuming 4 g/d MOS, attributed to an increase in fat excretion in the feces or inhibition of hepatic lipogenesis. Kumao et al. [55] observed a reduction in fat utilization and an increase in fecal fat excretion in people consuming 3 g/d of MOS for 7 days. St.-Onge et al. [56] also observed a reduction in body weight and adipose tissue following consumption of 4 g/d MOS for 12 weeks. Umemura et al. evaluated

have been recognized as a nutritional supplement for livestock.

*DOI: http://dx.doi.org/10.5772/intechopen.89484*

*Functional Attributes and Health Benefits of Novel Prebiotic Oligosaccharides Derived… DOI: http://dx.doi.org/10.5772/intechopen.89484*


#### **Table 4.**

*Prebiotics and Probiotics - Potential Benefits in Nutrition and Health*

For example, Mao et al. [23] found that 237 out of 453 strains (114 genera) of gut bacteria contained the necessary transporters and enzymes for some type/degree of FOS utilization, suggesting fairly widespread utilization of FOS, which will impact the effective dose required to grow the targeted beneficial bacteria. Similarly, Goh et al. [11] note the widespread ability of microbes to utilize lactose, suggesting the presence of LacS (or similar) transporters and enzymes in many microbes that

**64**

**Table 3.**

*Summary of clinical trials with XOS.*

*Summary of clinical trials with AXOS.*

would allow use of the GGan type of GOS. This is consistent with the observations of Makelainen et al. [31], who also observed excellent growth of many species, beneficial and pathogenic, on GOS (see also **Figure 4**). Ultimately, increased sharing of prebiotic substrates among bacteria means that a higher dose is needed to trigger sufficient growth of the targeted beneficial bacteria that produce the desired health benefits.

#### **4.2 MOS**

Manno-oligosaccharides (MOS), extracted from yeast cell walls, coffee or biomass rich in mannan, are typically comprised of up to 6 mannose subunits connected by β-1,4 bonds. MOS have not been as extensively evaluated in humans, but have been recognized as a nutritional supplement for livestock.

Salinardi et al. [54] observed a reduction in body volume and adipose tissue in men consuming 4 g/d MOS, attributed to an increase in fat excretion in the feces or inhibition of hepatic lipogenesis. Kumao et al. [55] observed a reduction in fat utilization and an increase in fecal fat excretion in people consuming 3 g/d of MOS for 7 days. St.-Onge et al. [56] also observed a reduction in body weight and adipose tissue following consumption of 4 g/d MOS for 12 weeks. Umemura et al. evaluated the impact of 1 g/d of MOS consumption on fecal microbiota and laxation [57]. They noted an increased ratio of *Bifidobacterium* spp., and enhanced defecation frequency/volume, reducing constipation. A study in mice by Zheng et al. [58] suggested that MOS acted synergistically with metformin, altering the gut microbiota in a manner that would decrease clinical diabetic parameters, including a reduction in blood glucose. This may have promise for future clinical trials and application of MOS plus metformin for management of type II diabetes.

Jahromi et al. [59] examined MOS supplementation (1 g/kg) to broiler chicks, and observed increased levels of *Lactobacillus spp*. and *Bifidobacteria spp*., while reducing levels of *E. coli* and *Enterobacter* by >50%. Navidshad et al. [60] compared MOS derived from yeast cell walls with MOS from palm kernel expeller, assessing their efficacy as a supplement (2 g/kg) to the diet of broiler chicks. The yeastderived MOS improved weight gain, while reducing the intestinal percentage of *E. coli* in the birds. MOS has been reported to have receptors for fimbriae on *E. coli*, which can help to control or limit colonization within the digestive tract [61]. Jahromi et al. [62] also evaluated *In Ovo* injection of MOS, and feeding of MOS to chicks. The single *In Ovo* injection had some short term but limited long term effects, other than an increase in *Bifidobacterium* spp. at 14 days. Feeding MOS in the diet markedly improved levels of *Lactobacillus* and *Bifidobacteria*, while reducing levels of pathogenic strains of *Salmonella*, *E. coli*, and *Campylobacter*. Adding MOS to the diet also improved levels of serum immunoglobulins IgA, IgM, and IgG. The immunomodulatory effect of MOS in chicks was stated to be a significant benefit that could help improve productivity, and reduce disease (thereby reducing use of antibiotics). Zhao et al. [63] studied the impact of supplementing 0.1 wt% MOS or 0.1 wt% FOS in weanling pigs over 28 days. They observed greater average daily weight gain and average daily feed intake in pigs consuming MOS compared to controls. Nutrient digestibility also improved, along with diarrhea score (potentially by inhibiting *E. coli*). Collectively, the authors concluded that MOS could enhance piglet growth and health.

## **5. Summary**

Increased understanding of enzyme and transporter expression in various microbes, and key differences between the various classes of enzymes and types of transporters, are enhancing our knowledge about microbial selectivity for substrates, including prebiotics. Differences in chemical structure, degree of polymerization, and bonds between subunits affect microbial utilization of prebiotics. Novel prebiotics derived from xylan, arabinan, and mannan are comprised of less common subunits based on 5 carbon sugars (xylose, arabinose), and/or are connected via β-bonds. The unique types of subunits and bond structures confer greater selectivity for beneficial bacteria, and health benefits at a lower dose compared to conventional prebiotics comprised of glucose, fructose and galactose subunits.

Clinical trials with XOS and AXOS led to improvements in laxation, triglycerides, cholesterol, and blood glucose, typically at doses from 1 to 3 g per day, far less than the 10–30 g per day required with FOS, GOS, inulin, and resistant starch. Preliminary clinical trials with MOS suggested the potential for weight management and reductions in adipose tissue at doses in the range of 4 g per day. Furthermore, MOS seems to have a unique capacity to inhibit proliferation of *E. coli*, and its addition to livestock feed has improved livestock health with a concurrent reduction in antibiotic use. Ultimately, these novel prebiotics may usher in a new era of prebiotic utilization, driven by their greater selectivity for beneficial bacteria, and easier product formulation and efficacy at a lower dose.

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**Author details**

Bradley A. Saville1,2\* and Sandra H. Saville2,3

2 Prenexus Health, Gilbert, AZ, United States

provided the original work is properly cited.

3 Saville Nutrition Consulting, Oakville, ON, Canada

\*Address all correspondence to: bradley.saville@utoronto.ca

Toronto, Toronto, ON, Canada

1 Department of Chemical Engineering and Applied Chemistry, University of

© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

*Functional Attributes and Health Benefits of Novel Prebiotic Oligosaccharides Derived…*

The co-authors are both affiliated with Prenexus Health, a company that

*DOI: http://dx.doi.org/10.5772/intechopen.89484*

**Disclosures and conflicts of interest**

produces xylooligosaccharide prebiotics.

*Functional Attributes and Health Benefits of Novel Prebiotic Oligosaccharides Derived… DOI: http://dx.doi.org/10.5772/intechopen.89484*
