The Gut, The Immune System Connection, and Intestinal Permeability

Most of us know the importance of having a healthy gut, because few things impact our daily routines, social activities or travel as the worry, pain and embarrassment of a malfunctioning digestive system. Planning your next move depending on bathroom availability isn’t much fun! However, most people don’t know that the digestive system is the foundation of our body’s health.  Gut-associated lymphoid tissue (GALT) represents almost 70% of the entire immune system and approximately 80% of plasma cells (mainly IgA-bearing cells – remember those from the immunity chapter?) reside in GALT.^{[1] [2] [3]}

As stated in You Are What You Eat, nutrition isn’t just about ingesting food, it is a complex process that involves digestion, absorption, assimilation, metabolism, and excretion. In addition, remember the neurotransmitter serotonin that helps regulate our mood, sleep, and digestion? 95% of the body’s serotonin is produced in the intestine!^[4] The relationship between our diet, digestion, microbiome, and the intestinal barrier greatly impacts our overall wellbeing.^[5]

The lining of the intestines acts as a barrier to allow only fully digested carbohydrates, fats, and proteins, as well as vitamins and minerals, to pass through and enter the bloodstream. Minerals such as potassium, magnesium and sodium diffuse through intestinal cells (enterocytes) while amino acids, fatty acids and glucose travel via active transport.^[6]The spaces between the enterocytes normally have tight junctions. Our intestinal epithelium is renewed approximately every 5 days to maintain the tight junction and intestinal barrier.^[7]

When we’re under stress, consume a poor diet, drink excess alcohol or use a lot of Non-Steroidal Anti-Inflammatory Drugs (NSAIDs) like Ibuprofen (see below), we can cause the lining of our small intestine to get more permeable, or leaky.^[8] To put it simply, increased intestinal permeability, better known as “leaky gut” or intestinal hyperpermeability, means things can get across the gut barrier that shouldn’t.^[9] When either the intestinal cells or their junctions are damaged, larger molecules in the intestines pass through into the blood.^[10] This includes incompletely digested proteins, bacteria or bacterial fragments, infectious organisms, and waste products, all of which stimulate the immune system to mount an attack against the invaders.^[11] This causes irritation and inflammation throughout the body.

Further, research on increased intestinal permeability suggests that it might play a role in inflammatory states, such as food intolerance or allergy,^[12] obesity and diabetes,^[13] rheumatoid arthritis,^[14] and ulcerative colitis,^[15] among others. Some people find, for instance, that identifying an unknown food intolerance can alleviate symptoms such as headaches, irritable bowel syndrome, fatigue, and a host of other issues.

So, what causes leaky gut and how can we prevent it? If we look at the causes of intestinal permeability, we can attribute it to our modern, face-paced lifestyle. Chronic stress is a major culprit, and while many of us don’t realize it because “that’s the way it is”, our go-go-go lifestyles lead us to maintain a chronic sub-clinical level of stress. The chapter on What is Stress, Anyway? gives a more in-depth look into this insidious condition that has such a detrimental effect on our bodies.

Poor diet is also a huge contributor to intestinal permeability. Toxic and inflammatory processed and fast foods, over-eating, and not getting enough nutrient-dense foods plays havoc with our health. Other culprits include food additives in processed foods, which mounting research has shown could be implicated in autoimmune diseases and trigger damage to intestinal cells,^[16] as well as environmental contaminants such as chemicals, pesticides and herbicides which impair the intestinal barrier and overtax our immune system.^[17]