The Role of the GI Tract in the Immune System

Every single body system plays a role in our immune health. It is important to keep our body systems working in harmony to promote proper functioning and quality of life.  One of the most vital systems in our body influencing the quality of our immune systems is the digestive system and gastrointestinal tract.  We all know – one of the main functions of the GI tract is to digest food, absorb the nutrients from the food we consume setting the body up for efficient assimilation, and turn our food into sources of energy for our body to use. We must begin by eating properly prepared and nutrient-dense food, we then must also be able to breakdown the foods we consume AND absorb the nutrients they contain. The immune system is a nutrient hog and needs a vast array of nutrients, essential fatty acids, amino acids, vitamins and minerals, and phytochemicals to function optimally. Our bodies depend on the health of the digestive system to provide and assimilate the digested nutrients into each and every cell.

Did you know, the GI tract also serves as a protective barrier against outside invaders such as bacterias, viruses, allergens, and other pathogens, deciding what gets in and what stays out. The GI  tract represents our most intimate contact with the outside environment. It is not only tasked with the responsibility of extracting the appropriate nutrients from the food we consume that we need to thrive but, also to maintain an appropriate balance of helpful and harmful microbes and act as a channel for waste removal.

Poor digestion of food as a result of inflammation, poor enzyme production, imbalances of bacteria, and poor food choices lead to nutrient malabsorption and the body no longer gets the nutrients it needs in the amounts needed for optimal health. In functional medicine and nutritional therapy we always address the foundations of health first-  a healthy digestive tract and digestive system are key to a healthy immune system and one of the most critical steps to optimal health and longevity. After all, almost 70% of the immune system begins in the GI tract

The digestive system includes three main lines of defense against invaders, physical barriers, innate, and adaptive immune systems.

HCL and pepsin in the stomach act as a barrier defense that neutralizes many pathogens before entering the intestines. HCL and pepsin also begin to chemically break down proteins from your diet. Protein digestion begins when you start chewing your food and continues down into the stomach. If proteins are not fully broken down, they can be converted into harmful byproducts. Adequate amounts of stomach acid is also needed to prevent the overgrowth of bacterias and other opportunistic pathogens. Pathogens and antigens that survive digestion in the stomach then encounter the Gut Associated Lymphoid Tissue aka GALT which is a specialized feature of the immune system that houses a large amount of the cells in the immune system. 

The small intestine has millions of little undulations and hairs called villi and microvilli, that absorb nutrients from broken-down food into the bloodstream where they are then carried throughout the entire body and keeps out harmful substances.  When food particles are not broken down completely due to poor digestion, these food particles are able to cross the barrier into the bloodstream. They have the capability of damaging what is called tight junctions in the intestinal wall lining. These same undigested food particles and microbes can now move through an inappropriately permeable intestine and into the bloodstream (known as “leaky gut”). The food particles may appear foreign to the body and trigger an aggressive immune response. When the integrity of the lining of the GI tract is compromised, it severely impacts the health of the entire body. Leaky Gut can contribute to allergies, anxiety, brain fog, eczema, inflammation, autoimmune diseases, and other degenerative health conditions.

The surface cells (called epithelial cells) that line the small and large intestines secrete a protective mucous, rich in antimicrobial proteins. Healthy epithelial cells require a healthy, diverse microbiome. GI function and health are strongly correlated with the commensal organisms living within the GI tract. Commensal bacteria attach to carbohydrates in mucous, eat them, then produce short-chain fatty acids that provide fuel for the epithelial tissue. Epithelial cells are able to maintain an effective physical barrier against bacteria colonization or invasion by pathogens, facilitate nutrient digestion and assimilation, and provide surveillance signals in the gut. This is a critically important part of the education and maturation of the immune system.

Healthy gut flora in the large intestines help stimulate the immune system, feed the epithelial cells, and crowd out pathogenic bacteria. The gut microbiome contains several classes of organisms including commensal bacteria, opportunistic bacteria, fungi, viruses, and pathogens. The interaction of multiple strains of bacteria and proper bacterial balance is vital for a healthy gut, healthy immune system, and overall health and wellbeing.

Nutrients in, waste out, remember the GI tract also acts as a channel for waste removal. Ridding the body of unusable portions of foods, as well as removing toxins and waste produces in the body is a critical function of the GI system. Without proper elimination, harmful inputs, and residents of the GI tract stick around and can be the effect of an unhealthy gut and immune system.

If you want to optimize your digestion and gut microbiome, contact in2GREAT Functional Medicine Clinic in Kansas City by filling out this contact form or by giving the office a call at (913) 308-0174. We offer a number of services, including functional lab testing, to see if your body contains heavy metals, toxins, harmful gut bacteria, and more.