Arabinoxylan and AXOS Fiber - Our Research Notes

Summary of our research

• Arabinoxylan (AX) is a subtype of fiber found in cereal grains, and AXOS is its isolated form extracted from foods.
• AX/AXOS has shown to have some beneficial effects on blood sugar levels 
• Ferulic Acid, a polyphenol, is bound to AX in wheat and has many potential health benefits.
• Several changes occur in the microbiome with AX/AXOS consumption, including increased bifidobacteria, increased SCFA production, and a shift in protein fermentation.
• Other potential benefits of AX/AXOS like bowel function, cholesterol mediating, and weight modulating need further studies. 
• Inadequate amounts of whole grains may cause unwanted changes in the microbiome.

Wheat and other gluten-containing grains have taken a hit over the past decade due to gluten being deemed unhealthy or a substance in food to avoid. More recently, lectins have been in the spotlight as a component of food to avoid. In grains, lectins are primarily in the outer hull/bran, and so the ideology of going lectin-free encourages refined grains or no grains at all.

This article discusses the benefits of Arabinoxylan (AX), a subtype of fiber found in the bran and endosperm portion of cereal grains like rye, oat, barley, wheat, corn, brown rice, sorghum, and pearl millet S(source, source) and arabinoxylan oligosaccharide (AXOS), the isolated form of AX extracted from food source S. 

AX and AXOS have been shown to have a positive effect on blood sugar levels. (s) Some animal studies have shown weight loss potential with AX supplementation. The more promising benefits of AX/AXOS are the potential roles as a prebiotic, SCFA producer, and antioxidant, as well as other changes in the microbiome.(S) Thus, unnecessarily removing grains from the diet may change the trajectory of the microbiome and overall health.

AX/AXOS Sources and Composition

Cereal grains differ in composition, with varying amounts of total dietary fiber, insoluble fiber, and soluble fiber (S). The quantity of AX in grains depends on the type of grain, as shown in the tables below. Further, each grain type can have varying amounts of AX depending on the year it was grown and the condition of the growing season. (s) The genus and species of the grain can also alter the amount and molecular structure of AX in a particular grain (S). 

Because AX comes from different grains and different parts of the grain, it can be categorized as both soluble and insoluble. About 25-30% of AX is water-soluble and highly viscous--and water-soluble AX rapidly ferments. Meanwhile, AX from hulls and brans are primarily insoluble and poorly fermentable (S).

When discussing AX sources and their impact on health, one further consideration is the preparation and processing of grains like milling, heating, flaking, or extrusion. Different processing of grains has been shown to affect in vitro fermentation differently depending on the grain. Grain fibers are not all equal in their potential for prebiotic effect, and the varying effects of preparation and processing of each grain further complicate this. (S)

AX in Cereal Grain Flours 

(s)

AX in Cereal Grains

Potential Benefit: Antioxidants

Ferulic acid, a type of polyphenol, has been deemed a ‘superior antioxidant’ because of its many abilities to improve health. 

Some benefits of ferulic acid:

• Anti-inflammatory
• Antimicrobial
• Anticancer
• Immune-modulating 
• Damaged cell repair (S)

In wheat, ferulic acid is bound to AX, allowing the ferulic acid to arrive into the colon. The slow continuous release of ferulic acid by the gut microbiota metabolism may increase circulating ferulic acid and its byproducts. When ferulic acid is in plasma or feces, it indicates that bacterial fermentation is occurring in the colon. (S) This could be why whole grain consumption is associated with various health benefits, such as decreased inflammation. (S) 

A study showed significant increases in stool and plasma ferulic acid in those who ate 70 g of whole grain wheat cereal daily compared to those who ate 60 g of refined wheat daily. (S) When AXOS was given in doses of 2.2 and 4.8 g, there was a dose-dependent increase in plasma ferulic acid. 

Potential Benefit: Bowel Function

Wheat bran fiber, estimated to be about 80% AX, has been studied for its health benefits. No significant difference was noted in fecal output or bowel habits when study participants were given 30 g of wheat bran fiber (S). However, the EU has approved wheat bran fiber to have the health claim of reducing intestinal transit time (in other words, increasing the speed at which stool passes through your GI system) when consuming 10 g/day.  (S).

Potential Benefit: Microbiome Changes

AX has major bifidogenic effects and can positively affect healthy microbes in the gut. (S) In one study, 2.2 g of AXOS produced a significant positive benefit to the gut microbiota. This indicates that a slight change in eating habits can have a significant prebiotic effect. Positives changes were also seen with 5.7 g wheat fiber, 10 g barley fiber, and 7 g rye fiber (S). AX/AXOS has shown the ability to increase bifidobacterium, increase SCFA production, and decrease protein fermentation--all beneficial for the microbiome. We found review articles claiming AX increased lactobacillus; however, we were unable to verify this claim (S).

Bifidogenic effect

Bifidobacterium species have been shown to:

• Modulate the immune system
• Have an anti-carcinogenic effect
• Secrete antimicrobial compounds; inhibit the growth of pathogenic bacteria
• Increase resistance to infection
• Produce SCFAs such as lactate and acetate while cross-feeding with butyrate producers
• Produce certain vitamins10,11

The bifidogenic effects observed with AXOS have been seen in doses as small as 2.2 g/day and generally observed in a dose of less than 4 g/day. (S) Significant increases in Bifidobacteria were also reported following administration of 2.25 g AXOS, two 3.75 g doses of AXOS, two 5 g doses of AXOS, and a single 8 g dose of AXOS. There was a dose-dependent bifidogenic effect when study subjects received 0 g, 2.2 g, and 4.8 g AXOS in ready-to-eat cereal, further solidifying the impact of AXOS on the microbiome. (S)

SCFA production

AXOS has increased acetate, propionate, and butyrate in healthy adults (S). However, the increase in SCFA type (acetate, butyrate, or propionate) depended on the study. Some studies did not observe an alteration of SCFA production after supplementation with AX-rich wheat-bran extract or AXOS. Further, a study even reported reductions in butyrate amounts. These discrepancies in findings could be due to the different structures of AX and how or if AXOS gets fermented. (S) (S) 

A change was observed in total fecal SCFA content when supplementing 8 g AXOS per day for 3 weeks. In this study, acetic, propionic, and butyric acid all significantly increased, and propionic acid was significantly increased with a lower dosage of 2.5 g AXOS. In a study where people received either 8.9 g AXOS, 18.4 g AXOS, or resistant starch, the findings showed a dose-dependent increase in acetate and butyrate compared to the group that received resistant starch. (S) 

Protein fermentation

High intakes of dietary protein lower the abundance of microbes that are associated with beneficial health effects. It is not clear whether this differs between proteins from animals or plants. (S) When study participants ate 10 g of AXOS, there was a significant reduction in compounds that form during protein fermentation. This indicates a shift away from protein fermenters and their potentially harmful byproducts. (S)

Adverse effects

AXOS had no reported symptoms at doses <4.8 g. One study had participants complain of flatulence with a 10 g supplement. Another study had no reported GI effects with 9.4 g x 4 doses over 48 hours. source source. Wheat bran extract, which we know to be highly concentrated with AX, showed no GI symptoms when given in quantities of 30 g/day. (S)

Our conclusion

The standout features of AX/AXOS are the changes in the microbiome and potential benefits from ferulic acid. As we mentioned, small amounts of fiber added to the diet can greatly impact the microbiome(S).

The primary source of AX in the American diet comes from gluten-containing grains: wheat, rye, barley, and oats (sometimes cross-contaminated with gluten). (S)

And while other foods contain AX, there are potentially different effects with differing sources of AX/AXOS. Currently, evidence suggests that increasing the amount of fiber and diversity of foods consumed to promote microbial diversity could help to maintain or improve health (S). If you think you need to cut out gluten from your diet, talk to your doctor and check out our article on the Gluten-Free Diet. 

If you want to bump your AX intake, breakfast often provides a significant contribution to daily fiber intakes in western populations. Breakfast is an occasion where switching to higher fiber foods may be a bit easier. (S)

Eating 2 slices of whole-grain toast, oatmeal, or whole-grain cereal may be enough to boost your AX intake and provide you with the benefits discussed in this article. Further research is needed for whether a single boost of fiber is different than eating fiber throughout the day. (S)