Why is gut barrier integrity important?

Every day, your gut interacts with your inputs—the foods you eat, the molecules you breathe, and sometimes, potential toxins (i.e., NSAIDs like aspirin, alcohol, and even high-intensity workouts). As a critical line of defense, the gut barrier must carefully regulate what it allows in, and what it keeps out. 

To do this, the gut barrier has three major lines of defense¹:

1. The biological barrier. Also known as the mucus barrier. This mucus layer consists of intestinal microbes, which play a crucial role on the gut intestinal track by making it difficult for inhospitable bacteria to penetrate. They help maintain an acidic environment to dissuade certain alkaline-loving pathogens from taking root. They also support the secretion of intestinal mucus and collaborate closely with the cells of your gut lining to limit gut permeability.
2. The immune barrier. This consists of tissue known as GALT (gut-associated lymphoid tissue), which represents 70% of the entire immune system², ⁣in addition to various immune cells. This barrier fosters communication between the immune system and gut, a relationship known as the gut-immune axis, which is vital to managing immune response to both harmless inputs (like nutrients) and harmful ones (like pathogenic bacteria).
3. The mechanical barrier. This consists of a single layer of intestinal epithelial cells, held together by structures called tight junctions. Tight junctions are intercellular connectors that form scaffolding in the gut barrier to reinforce its’ integrity and keep out foreign materials and contaminants. (Fun fact: your resident microbes also support the presence of tight-junctions). 

So, what happens when these lines of defense falter? 

By nature, the gut is permeable, to allow essential inputs to pass through into the body. However, if the gut barrier is damaged or compromised, the permeability of the gut can increase, allowing substances that don’t belong in your body to enter the bloodstream. This is known as intestinal hyperpermeability, leaky gut, or gut barrier dysfunction.

What causes leaky gut?

A variety of factors may contribute to leaky gut, and research is still uncovering what causes, and what exacerbates, increased intestinal permeability.

Some factors that may damage the gut barrier: 

• Chronic inflammatory states, like Inflammatory Bowel Disease³ and celiac disease⁴
• Overuse of alcohol or NSAIDs
• Food allergies that trigger an immune response 

Another key area that researchers are looking at is the role of the gut microbiome in gut barrier function. Homeostasis of the gut barrier depends on the relationship between gut microbiota and the intestinal epithelium. Dysbiosis of the gut microbiota (an imbalance in the composition) could contribute to leaky gut. One way this works: dysbiosis can result in an increased population of pathogenic microbes, which can damage gut epithelial cells.⁵

Diet is also a major focus when it comes to leaky gut, as dietary components are in frequent contact with the gut barrier, and are likely to play a role in regulating gut microbiota and intestinal permeability. Studies have shown that fats can promote an increase in epithelial permeability. On the other hand, dietary fiber is widely recognized as a protective nutrient for the gut barrier, and also contributes to maintaining a healthy state for gut microbiota. This suggests that Westernized diets, high in fat and lacking fiber, could impair intestinal barrier function.⁵

What are signs of leaky gut?

Leaky gut can cause a range of gastrointestinal issues, like diarrhea, gas, and bloating. But the effects of leaky gut extend beyond just your GI tract, as unwelcome guests trigger immune responses like inflammation, allergies, irritable bowels, migraines, fatigue, and more.⁶

The 30-foot tube that makes up your gastrointestinal tract is host to the world passing through. The gut is in constant contact with external inputs—from the air you breathe to the foods and beverages you consume. The integrity of the gut barrier is essential for both allowing beneficial inputs (like nutrients)  in and protecting against potentially harmful ones (undigested food particles, pathogens). 

The best way to support your gut barrier is to take care of your overall digestive and gastrointestinal health. One simple place to start: probiotics. Certain probiotic strains have demonstrated the ability to influence mucus composition and enhance the gene expressions involved in tight junction signaling.⁷ Translation: they can promote the integrity and “tightness” of your gut barrier. 

1. Assimakopoulos, S. F., Triantos, C., Maroulis, I., & Gogos, C. (2018). The Role of the Gut Barrier Function in Health and Disease. Gastroenterology research, 11(4), 261–263. https://doi.org/10.14740/gr1053w
2. Wiertsema, S. P., van Bergenhenegouwen, J., Garssen, J., & Knippels, L. (2021). The Interplay between the Gut Microbiome and the Immune System in the Context of Infectious Diseases throughout Life and the Role of Nutrition in Optimizing Treatment Strategies. Nutrients, 13(3), 886. https://doi.org/10.3390/nu13030886
3. Chadwick, V. S., Phillips, S. F., & Hofmann, A. F. (1977). Measurements of intestinal permeability using low molecular weight polyethylene glycols (PEG 400). I. Chemical analysis and biological properties of PEG 400. Gastroenterology, 73(2), 241–246.
4. Bjarnason, I., Marsh, M. N., Price, A., Levi, A. J., & Peters, T. J. (1985). Intestinal permeability in patients with coeliac disease and dermatitis herpetiformis. Gut, 26(11), 1214–1219. https://doi.org/10.1136/gut.26.11.1214
5. Usuda, H., Okamoto, T., & Wada, K. (2021). Leaky Gut: Effect of Dietary Fiber and Fats on Microbiome and Intestinal Barrier. International journal of molecular sciences, 22(14), 7613. https://doi.org/10.3390/ijms22147613
6. Takeda, Y., Nakase, H., Namba, K., Inoue, S., Ueno, S., Uza, N., & Chiba, T. (2009). Upregulation of T-bet and tight junction molecules by Bifidobactrium longum improves colonic inflammation of ulcerative colitis. Inflammatory bowel diseases, 15(11), 1617–1618. https://doi.org/10.1002/ibd.20861
7. La Fata, G., Weber, P., & Mohajeri, M. H. (2018). Probiotics and the Gut Immune System: Indirect Regulation. Probiotics and antimicrobial proteins, 10(1), 11–21. https://doi.org/10.1007/s12602-017-9322-6