Most of the nutrients we consume are broken down and absorbed in the small intestine, fermented by gut bacteria in the colon or passed through undigested. In a healthy person, the gut wall is selectively permeable, only allowing some luminal content such as properly broken down nutrients to pass into the bloodstream. A “leaky gut” or increased intestinal permeability indicates that the intestinal lining has become hyperpermeable and allows unwanted substances to pass into the body. While the existence of a leaky gut syndrome long was debated among doctors and scientists, studies published in the last couple of years have made it clear that increased intestinal permeability not only is a real condition, but an important underlying cause of inflammation and disease.
The intestinal epithelium is the epithelium that covers the small and large intestine, and this lining serves as an interface between the human body and the external environment. The epithelial cells in the small intestine are joined together by tight junctions, and when we talk about a leaky gut, it’s primarily these intestinal junctions that have become hyperpermable (1).
Leaky gut causes low-level chronic inflammation
When the intestinal barrier is compromised, luminal content such as protein antigens and endotoxins (toxins released by bacteria) are allowed to pass into the bloodstream (2,3). The primary toxin associated with increased intestinal permeability is a large molecule found in the outer membrane of gram negative bacteria, called Lipopolysaccharide. When LPS binds to the cells lining the gut, there’s an increased synthesis of proinflammatory cytokines (4,5).
The gut immune system has 70-80% of the body’s immune cells (6). When we consider the gut as the primary immune organ, it’s no surprise that gut dysbiosis and leaky gut have been linked to inflammation and disease. Alterations in the gut microbiota usually go hand in hand with leaky gut since one of the primary jobs of the bacteria in the gut is to regulate intestinal barrier function.
Inflammation linked to chronic health disorders
Studies suggest that low-level inflammation drives most of the chronic health disorders we see in the world today, such as cancer and cardiovascular disease (7,8). Since “leaky gut” only recently has been accepted by the medical community as a real conditions, it’s to early to tell which role gut-derived inflammation plays in the development of a lot of chronic health problems. However, increased intestinal permeability has already been associated with disorders such as obesity, autoimmune disease, and irritable bowel syndrome (9,10,11).
Since low-level chronic inflammation is linked to most chronic health disorders, symptoms of a “leaky gut” could be everything from acne to heart disease. Sometimes, increased intestinal permeability causes no immediate symptoms, but the long-term low-grade inflammation could initiate disease. When the gut lining has become hyperpermeable, gut dysbiosis or dysfunctional gut flora is usually involved. For that reason, moderate-severe cases of leaky gut often involve constipation, flatulence, food intolerance, bloating, and/or other digestive problems.
Because so many aspects of the modern lifestyle, such as widespread use of antibiotics, western diets, caesarean sections, are linked to gut dysbiosis and leaky gut, I believe that increased intestinal permeability is a major cause of chronic disease in the world today.