Arabinoxylan is a dietary fiber found within the cell walls of plants, particularly cereal grains. As a complex carbohydrate composed of arabinose and xylose sugars, it cannot be broken down by human digestive enzymes. This resistance to digestion allows it to travel to the large intestine where it can be fermented. This process contributes to the health benefits associated with consuming whole-grain foods.
Food Sources of Arabinoxylan
Arabinoxylan is most abundant in the outer layers of cereal grains. The bran, which is the hard outer part of grains like wheat, rye, and barley, contains the highest concentrations. For instance, wheat bran can be composed of 20-30% arabinoxylan, while rye bran may contain up to 40%. For this reason, products made from whole grains are better sources than their refined counterparts, from which the bran and germ have been removed.
Corn bran is another notable source of this fiber, and psyllium husk, derived from the seeds of the Plantago ovata plant, is also a significant source. Opting for whole wheat bread over white bread, or choosing whole grain cereals, ensures a much higher consumption of this beneficial fiber.
Function as a Prebiotic Fiber
The primary role of arabinoxylan in gut health is its function as a prebiotic, a substance that serves as food for beneficial microbes in the gut. After arriving in the colon, it is fermented by specific species of beneficial bacteria, most notably those from the Bifidobacteria genus. This fermentation process results in the production of beneficial compounds called short-chain fatty acids (SCFAs), primarily butyrate, propionate, and acetate. Butyrate, in particular, serves as the principal energy source for the cells lining the colon, known as colonocytes, helping maintain the integrity of the gut lining. The production of butyrate also creates a more acidic environment in the colon, which is less hospitable to potential pathogens, and it has well-documented anti-inflammatory properties.
Impact on Metabolic Health
Arabinoxylan influences metabolic health as a soluble fiber, absorbing water to form a viscous, gel-like substance in the digestive tract. The formation of this gel slows the emptying of the stomach and the movement of food through the small intestine. This leads to a more gradual absorption of glucose into the bloodstream. By blunting the sharp spikes in blood sugar that can occur after a meal, arabinoxylan helps promote better glycemic control.
This viscous gel also interferes with the absorption of cholesterol by binding to bile acids in the small intestine. Bile acids, produced from cholesterol in the liver, are necessary for digesting fats. By trapping these bile acids and carrying them out of the body through waste, arabinoxylan forces the liver to pull more LDL cholesterol—often called “bad” cholesterol—from the bloodstream to produce new bile acids, helping to lower overall levels.
Role in Immune System Support
The influence of arabinoxylan on the immune system is connected to its effects on the gut microbiome. The gut is a major site of immune activity, housing the gut-associated lymphoid tissue (GALT), a complex network of immune cells responsible for a significant portion of the body’s immune surveillance. A healthy and diverse gut microbiome is important for the proper functioning of the GALT.
By acting as a prebiotic, arabinoxylan helps maintain a balanced gut environment. This well-nourished microbial community communicates with the immune cells in the GALT, helping to regulate immune responses and prevent inappropriate inflammation. The short-chain fatty acids produced during its fermentation also play a role in modulating immune cell activity.
Research also suggests a more direct interaction between the breakdown products of arabinoxylan and the immune system. Certain fragments released during its fermentation may act as signaling molecules that can influence the behavior of immune cells. Through both its indirect support of the GALT and direct signaling, arabinoxylan contributes to a well-regulated immune system.