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By Monica Echeverri

“…fiber-derived metabolites play a vital role in increasing microbial diversity, reducing inflammation, and modulating the immune response.”

As cold and flu season approach, the familiar “immune boosting” supplements and remedies may start entering our medicine cabinets. While taking supplements can certainly help increase levels of vitamin C and zinc, experts suggest a more long-term approach. The way our gut interacts with different types of food, particularly fiber, is revealing how a fiber-rich diet can be helpful for supporting our immune system. Research shows that a stable environment in the gut leads to numerous beneficial effects on the body’s physiological, metabolic, and immunological functions. This is because fiber-derived metabolites play a vital role in increasing microbial diversity, reducing inflammation, and modulating the immune response.

Increase Microbial Diversity

To maintain a healthy immune system, it’s important to consider the connection between the immune cells in our gut and the microbiome – the vast ecosystem made up of trillions of bacteria, viruses and fungi in the gastrointestinal tract. Research has discovered that about 60% of immune cells reside in gut tissue (the gut-associated immune system), suggesting a strong connection between the gut and immune system. For this reason, microbial composition has been evaluated for its role in immune health. Studies reveal that imbalances in microbial diversity may contribute to immune-related disorders. For example, individuals with rheumatoid arthritis, an autoimmune disease, have higher levels of microbial taxa that are associated with inflammation. In individuals with inflammatory bowel disease (IBD), alterations of the gut microbiome are strongly associated with immune responses that contribute to intestinal inflammation and tissue injury. These individuals also have notable shifts in abundance of certain microbial taxa, such as decreased levels of Bacteroides and Lactobacillus strains. However, most human studies have only shown associations, not a causal relationship between altered microbes and inflammation.

“…the American Gut Study found that eating 30 plant-based foods per week can lead to the highest levels of gut microbial diversity!”

An individual’s lifestyle and diet can directly impact the diversity and composition of gut bacteria. Fruits, vegetables, grains, nuts, and seeds are all excellent sources of dietary fiber. In fact, the American Gut Study found that eating 30 plant-based foods per week can lead to the highest levels of gut microbial diversity! Not only do these foods contain different types of fiber, but also micronutrients, essential fatty acids, and other beneficial substances that have been associated with overall health. For example, the prebiotics inulin and oligofructose, stimulate the growth of bifidobacteria in the colon, which break down these fiber molecules into short-chain fatty acids (SCFAs) which have a beneficial effect on the gut-associated immune system. Therefore, consuming an adequate amount of dietary fiber is a therapeutic intervention for improving microbial diversity and richness as well as immune function.

Reduces Inflammation

“Research shows that one way to reduce chronic low grade systemic immune activation is to increase the consumption of dietary fibers.”

Inflammation is the immune system’s response to harmful stimuli. It is a defense mechanism that is vital to health, but uncontrolled chronic engagement of the immune system has been associated with a variety of chronic non-contagious diseases. Research shows that one way to reduce chronic low grade systemic immune activation is to increase the consumption of dietary fibers. The SCFAs generated by the gut microbes from these fiber molecules can reduce local and systemic immune activation in addition to reducing intestinal pH and membrane permeability. Research suggests that decreasing intestinal pH, making the environment more acidic, changes microbiota composition. This, in turn, inhibits the growth of harmful bacteria and lowers inflammatory markers. Additionally, SCFAs may also reduce inflammation by decreasing intestinal permeability. This reduced permeability may occur by increased production of proteins that help tighten and maintain gut barriers. By preserving healthy gut barriers, SCFAs can prevent the passage of microbial membrane fragments or entire microbes into the gut-associated immune system and the release inflammatory mediators, such as cytokines into the systemic circulation. While these mechanisms need further research, they offer clues into how consuming dietary fibers may regulate the immune system by reducing the inflammatory response.

“Other than prebiotics, researchers have discovered primarily in preclinical studies, that probiotic strains, especially when combined with prebiotics, can largely influence the immune system.”

Scientists have found that the microbiome plays a crucial role in immune function, with the gut being a significant location of immune activity. Once they have been fermented in the colon, dietary fibers, such as prebiotics, are turned into SCFAs in the colon. Among the SCFAs scientists have discovered that butyrate influences activity of an enzyme (histone deacetylases) which is responsible for decreasing immune cell activity. Other than SCFA’s, one study found that prebiotics inulin and oligofructose can directly activate receptors on immune cells that modulate the immune system. Dietary fibers have also been found to inhibit receptor activation, which could lead to reduced secretion of cytokines, or proteins that control immune cell activity. Other than prebiotics, researchers have discovered primarily in preclinical studies, that probiotic strains, especially when combined with prebiotics (so called synbiotics), can largely influence the immune system. Specifically, they noted that their immune-modulatory effects may be most potent when administered early in life. These findings reveal that consuming dietary fiber and having a healthy microbiome may modulate the immune system, mainly through inhibitory effects.

“Optimal functioning of the gut-associated immune system requires dietary constituents, especially prebiotics and fiber.”

The human gastrointestinal tract is the largest immune organ in the body. Optimal functioning of the gut-associated immune system requires dietary constituents, especially prebiotics and fiber. Prebiotics stimulate the growth of health-promoting bacteria in the colon, like inulin and oligofructose, which promote the growth of bifidobacteria, generating anti-inflammatory SCFAs and the anti-inflammatory cytokine IL-10. Based on a body of preclinical research, bifidobacteria provides various health benefits such as protection from intestinal infection, reduction of the number of potentially harmful bacteria, production of vitamins and antioxidants, assistance in digestion and absorption, potential reduction in the risk for colorectal cancer, and much more. These findings demonstrate that increasing dietary fiber consumption is a simple way to manipulate the gut microbiome and its metabolic functions, with significant potential to promote metabolic and immune health.

Monica Echeverri holds a Master of Science in Human Nutrition and Functional Medicine from the University of Western States and currently works as a food photographer, writer, and recipe developer for natural food brands and wellness publications. She has experience in community nutrition education and enjoys spending her time in the kitchen creating healthy recipes that she shares on her Instagram, @mealsbymonica.