The gastrointestinal tract plays a major role in digestion, the immune system, and the production of hormones and neurotransmitters. It processes food and absorbs nutrients and water while excreting and keeping out unwanted toxins. The lining of the intestines acts as a barrier that allows fully digested foods to pass through its lining and enter the bloodstream. The cells that line the intestines act as a filter between the environment and the body. Without the GI tract barrier, our bodies would reject all food that we ingest. The body sees food as a foreign substance. Foreign substances that produce an inflammatory immune response are known as antigens. The role of the GI tract is to keep out all antigens that are detrimental to the body. Antigens include food, bacteria, and toxins (anything that is foreign to the body).

Here is an example of how the GI tract protects us. Animal protein is a good source of protein for muscles. A doctor should theoretically be able to inject animal protein directly into your biceps to build muscle. This would assure that the protein goes directly to your muscles.

However, if a doctor did this, within hours your body would be overwhelmed by the injection of this foreign substance. Inflammation and infection would spread throughout the bloodstream to all parts of the body. It would lead to inflammation and sepsis (total body infection). If the protein is not removed and the infection and inflammation are not treated soon enough, death would quickly ensue. The GI tract, however, allows us to take in foreign substances such as an animal protein on a daily basis without any inflammatory response. Therefore, the protective role of the GI barrier is critical in that it allows us to ingest the foods that we need without potential deadly consequences.

Unfortunately, under stress, this protective mechanism and other functions of the GI tract are disrupted. The GI tract contains the largest part of the body’s immune system in its mucosal (inner) lining. The GI immune system’s role is to ensure that unwanted entities don’t cross the GI tract and enter the blood. The gastrointestinal tract is the first line of defense against pathogens, which enter the body through the food we ingest. However, under stress, unwanted pathogens (bacteria and viruses that can cause disease), toxins, and food substances are not destroyed by the immune system and are allowed to cross the barrier, leading to infection and inflammation throughout the body.

To make matters worse, stress decreases saliva production and digestive enzymes; therefore, food is not completely digested. Undigested foods irritate and damage the intestinal lining, making them more permeable. The intestinal mucosal cell junctions loosen and allow unwanted matter in the intestines to pass through into the blood. These unwanted substances trigger the immune system and lead to an inflammatory reaction.

Consequently, food allergies are likely to develop during times of stress due to the undigested food entering the blood and causing an inflammatory reaction. This inflammatory reaction can lead to inflammatory and, in some cases, autoimmune diseases. Individuals diagnosed with food sensitivities and inflammatory and autoimmune diseases should be evaluated for GI dysfunction.

In addition, digestive acid production decreases while gastric (stomach) emptying into the intestines diminishes. Harmful bacteria that reside in the intestines and normally controlled by gastric acid are now able to flourish. An antibody known as secretory SIgA is contained in intestinal mucus and destroys many of these microorganisms. But SIgA is decreased by stress which contributes to further pathogen overgrowth. Large intestinal motility increases under stress, which hinders the primary role of the colon in the absorption of nutrients and water.