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Increased Intestinal Permeability (Leaky Gut)

Photomicrographs of immunohistochemistry on small intestinal tissues from a healthy control and an active CD patient stained with zonulin cross-reacting anti-Zot antibodies. Zonulin is visualized both in enterocytes and in cells of the lamina propria (arrows) and is overexpressed in active CD patients compared with controls.

In small intestinal tissues Zonulin is seen both in enterocytes and in cells of the lamina propria (arrows) and is overexpressed in active CD patients compared with controls. Courtesy Dr. Alessio Fasano.

What Is Increased Intestinal Permeability?

Increased intestinal permeability is characterized by greater than normal intestinal permeability (leakiness) allowing for the penetration of harmful entities into the bloodstream such as undigested proteins and microbes. The popular name is “leaky gut.”

Q: Why does intestinal permeability increase?

A: Intestinal permeability is an essential function of the small intestinal mucosal lining by which wanted substances such as properly digested foodstuffs are allowed to permeate through the lining to enter the body via the bloodstream and lymphatics. At the same time unwanted substances are kept out.

The mucosal lining is one cell thick, which comprises the surface toward the digested foodstuffs inside the hollow of the intestine. This single layer of epithelial cells separates the contents of our small intestine from the lamina propria (underlying tissues of the small intestine) and the rest of our body. Breaching of this single layer of cells can expose effector immune cells located in the lamina propria to a myriad of microorganisms and food antigens, leading to immune reactions.1

To protect the body from unwanted substances, a gatekeeping barrier system operates to regulate the passage of nutrients, or permeation, through the surface mucosal lining.

The integrity of intestinal permeability is determined by interactions among several barrier components including the unstirred water layer, mucosal surface hydrophobicity, the surface mucous coat, and epithelial cell factors (especially tight junctions).

Tight junctions hold cells tightly together side-by-side to prevent unwanted substances from passing through the lining. Tight junctions are complex structures comprising over 50 proteins, such as the claudin proteins which are considered to be the structural backbone of tight junctions. Tight junctions include a series of transmembrane proteins, which form fibrils that cross the plasma membrane and interact with proteins in the adjoining cells. Tight junctions are regulated by the protein zonulin.2

If zonulin deregulates from the action of substances such as gliadin (gluten in wheat) and bacteria, the tight junction barrier fails which results in increased intestinal permeability. Dysfunction of the barrier system allows unwanted substances to enter the body where they are damaging to many tissues.

Tight junction dysfunction has been shown to be a part of certain autoimmune diseases such as celiac disease, type I diabetes mellitus, multiple sclerosis, and rheumatoid arthritis. Other diseases associated are cancer, allergies, and infections.3

Important gastrointestinal infections that cause leaky gut include rotavirus, parasites, pathogenic bacteria (escherichia coli, clostridium difficile), and mycotoxins produced by fungi found in stored grain and dried fruit.4

Fortunately, the presence of some commensal (friendly intestinal bacteria) and probiotic strains leads to an increase in tight junctions  proteins at the cell boundaries and in some cases prevents or reverses the adverse effects of pathogens, food and stress. Various dietary components are also known to regulate epithelial permeability by modifying expression and localization of  tight junctions proteins.5

What Is Increased Intestinal Permeability In Celiac Disease and/or Gluten Sensitivity?


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  1. Fahardi A, Banan A, Fields J, Keshavarzian A. Intestinal barrier: an interface between health and disease. Journal of Gastroenterology and Hepatology. 2003; 18: 479-497. 

  2. Ulluwishewa D, Anderson RC, McNabb WC, Moughan PJ, Wells JM, Roy NC. Regulation of tight junction permeability by intestinal bacteria and dietary components. J Nutr. 2011 May;141(5):769-76. doi: 10.3945/jn.110.135657.  

  3. Fasano A. Zonulin and Its Regulation of Intestinal Barrier Function: The Biological Door to Inflammation, Autoimmunity, and Cancer. Physiological Reviews. January 2011Vol. 91no. 151-175DOI: 10.1152/physrev.00003.2008 

  4. Farhadi A, Banan A, Fields J, Keshavarzian A. Intestinal barrier: an interface between health and disease. Journal of Gastroenterology and Hepatology. 2003;18:479-91. 

  5. Ulluwishewa D, Anderson RC, McNabb WC, Moughan PJ, Wells JM, Roy NC. Regulation of tight junction permeability by intestinal bacteria and dietary components. J Nutr. 2011 May;141(5):769-76. doi: 10.3945/jn.110.135657.  

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