The gastrointestinal (GI) tract functions not only to absorb nutrients but also to support important immunologic defenses during health and critical illness. Under experimental and certain clinical conditions, gut stimulation attenuates the stress response, limiting mucosal atrophy and increased gut permeability. Gut stimulation prevents atrophy of the gut-associated lymphoid tissue (GALT), the body's major defender of mucosal surfaces. The GALT is an important producer of IgA antibody and consists of Peyer's patches, lamina propria lymphocytes, and intraepithelial lymphocytes. IgA prevents the adherence of microbes to the moist mucosal surfaces throughout the body, preventing an essential first step for systemic invasion. Immunonutrition may become an important adjunct to augment the body's natural defense systems and to reduce the need for these invasive therapies. A better understanding of gut function and improved nutrient delivery has clinical implications in the treatment of all patients.  

With the overuse of anti-biotics, the gut flora is often compromised and needs to be replenished with a quality probiotic.  Food sensitivities can create an increased gut permeability that provides an environment for an autoimmune cascade.  Also, the connection between the GI tract and neurotransmitters is often overlooked.