During the last decade, new knowledge about our intestinal gut microbiota and its interaction with the host’s immune system has emerged. One of the most important food components affecting the composition of the gut microbiota are soluble dietary fibers.
Dietary fibers are not digested by human digestive enzymes and therefore reach the colon. Here the beneficial gut microbes thrive on the soluble dietary fibers and prebiotics from the food we consume each day and produce tiny metabolites called short-chain fatty acids (SCFA). The SCFA have been difficult for scientists to study due to their location. Recent findings show that these SCFA, in particular butyrate, have enhancing effects on our immune system.
Consumption of soluble dietary fibers leads to increases in beneficial gut bacteria such as the bifidobacteria, and prebiotics are especially strong in stimulating bifidobacteria. These bacteria with the help of others give greater levels of SCFA. SCFA maintain an environment favorable for our microbiota and these in turn control pathogens’ growth. Furthermore, as these SCFA will be absorbed into the bloodstream, they will reach and positively affect other parts of our immune system and our organs as well.
Importantly, SCFA can increase anti-inflammatory and decrease pro-inflammatory mediators in our whole body, and thereby promote a balanced mucosal immune system. SCFA can do this by binding to special receptors, called G protein coupled receptors (GPCR), which are present on the cells of many of our organs. Remarkably, especially the SCFA ‘butyrate’ regulates the expression of hundreds of our human genes, which modulates our immune system. Moreover, emerging evidence shows that SCFAs act on the bone marrow, to promote the generation and development of immune cells, so diet and microbiota are linked to the gut-lung axis. Another route to improve the immune system is that some prebiotics with specific structures can directly bind to receptors on immune cells in the intestine.
Altogether, the fiber-SCFA effect is to trigger immune reactions which support immunity against infections and reduce inflammation. The intestinal immune system can interact with and be influenced by components of our diet. Consequently, the intestine is the site where dietary fibers and prebiotics can exert their effects on the immune system.
Download the paper Immunity and inflammation: valuable role for prebiotic fibers