What is XOS? A New Kind of Prebiotic

The use of prebiotics to enhance and improve the balance of commensal bacteria in the gut is not new. In fact, many probiotic formulas now include one of the more commonly used forms of prebiotics, such as fructooligosaccharides (FOS), arabinogalactan, galactooligosaccharides, beta-glucan, and inulin. But now there’s a new kid on the block – xylooligosaccharides – and this one sports some unique characteristics that make it a favorable choice.  

Xylooligosaccharides (XOS) are impressive. The basic structure consists of sugar oligomers composed of xylose units, found naturally in fruits, vegetables, milk, honey and bamboo shoots. Unlike other forms of prebiotics, xylooligosaccharides are effective at lower doses. Why might this be important? Patients taking prebiotics often notice an increase in many of the same symptoms they are trying to resolve by optimizing their disordered microbiome; namely, bloating and abdominal pain. Naturally, these outcomes are a result of the commensal bacteria fermenting the prebiotic fibers and releasing gaseous byproducts. Most patients would not welcome a worsening of the very issues they’re trying to get rid of. The probiotics may be getting a feast to help them grow, but the misery resulting from this feast often leads the patient to discontinue the prebiotics. However, since xylooligosaccharides can effectively simulate the growth of probiotics at lower doses, the unpleasant side effects of most other prebiotics are not present. Patients may be more likely to continue taking xylooligosaccharides, and their commensal bacteria will be happy for the ongoing food source.

The lack of unpleasant gastrointestinal symptoms is not the only reason to prefer xylooligosaccharides. A recent study on 32 healthy adults was conducted to determine the tolerance and effects of the prebiotic xylooligosaccharide (XOS) on the composition of human colonic microbiota, pH and short chain fatty acids (SCFA) in order to determine whether significant changes in the microbiota would be achievable without side effects.” (1) Subjects received 1.4 g XOS, 2.8 g XOS or placebo for 8 weeks. Xylooligosaccharide resulted in a significant increase in the genus Bifidobacterium, compared to placebo.

One of the most touted advantages of xylooligosaccharides is their selectivity to Bifidobacteria, as evidenced in an in vitro fermentation study using human fecal samples and five different types of prebiotic fibers. Increasing this specific phyla of bacteria has been associated with numerous health ooutcomes including decreased bloodlipopolysaccharides (LPS), which are linked to inflammatory metabolic conditions. LPS induce the activation of Toll-like receptor 4 (TLR4), leading to the release of pro-inflammatory cytokines and chemokines. A lack of Bifidobacteria has been observed on obesity and weight gain, making xylooligosaccharide a potential therapeutic agent in improving body composition.

Another unique benefit of increasing Bifidobacteria is that no gas is formed with their metabolic end products. This effect offers another explanation for the absence of gastrointestinal symptoms when taking xylooligosaccharides compared with other prebiotics.

Xylooligosaccharides not only help to establish the right kind of commensal bacteria, but they also improve structural elements of the gut. In a recent animal study, examining prebiotic effects of xylooligosaccharides on intestinal characteristics among 1,080 test subjects (laying hens), it was found that villus height, the villus to crypt depth ratio, and the relative length of the jejunum increased significantly with dietary xylooligosaccharides. This same study also noted an increased content of acetic acid and the SCFA butyrate, which results in acidification of the colonic environment and fuels colonocytes, respectively. Together, these functions are vital for optimizing cellular processes in the microbiome. Increases in immune factors IgA, IgM, TNF-α, and IL-2 also suggest improved functional health of the microbiome since immunity is directly linked to the health of the microbiome.

With such beneficial and far-reaching applications, the emerging prebiotic fiber, xylooligosaccharide, seems to own the right to boast of being a high-quality agent for improving gastrointestinal health without the undesirable side effects of most prebiotic fibers, creating a win-win situation for the patient.

- Designs for Health