The second major function of the small intestine is a protective one. It prevents toxic substances and large molecules, such as large protein molecules, from getting into the bloodstream. These large molecules cannot be handled well by the body and frequently cause the immune system to produce antibodies against them. This then may result in a series of inflammatory reactions that characterize food allergy reactions. They may also stimulate the body to produce antibodies against its own tissues, resulting in autoimmune disease as seen in some forms of arthritis and inflammatory bowel disease. When large molecules break through the intestinal barrier to enter the bloodstream, the patient is said to have increased intestinal permeability or a leaky gut.

The leaky gut itself may be caused by food allergy reactions, resulting in a vicious cycle, or by infections or toxic agents. Once a leaky gut is identified, it is important to correct the underlying cause or causes and also to attempt to repair the damage to the intestine, so that the leaky gut is corrected.

Recently, a simple test has become available commercially to test for a leaky gut. The patient is given a kit in order to do the test at home. The patient drinks a solution containing a known quantity of two sugars, namely mannitol and lactulose. Normally, the body is able to absorb mannitol, but not lactulose. Urine is collected for six hours and sent to a laboratory, where the mannitol and lactulose concentrations and total amounts are measured. Normal ranges have been established. If excessive amounts of lactulose are present, then a leaky gut is likely. If, on the other hand, insufficient amounts of mannitol are present, then malabsorption is present. Either way, treatment measures may be introduced.

Causes of Intestinal Permeability (Leaky Gut or Malabsorption)
Damage to the lining of the intestinal wall may bring about either poor absorption of necessary nutrients or the absorption of large or toxic molecules that may cause damage to the system, resulting in the so-called leaky gut. This damage may be caused by infectious agents, toxic substances, food allergies or intolerances, deficiencies of pancreatic enzymes or autoimmune processes, in which the body makes antibodies against its own tissues.

One of the first steps to take in trying to understand the cause of a damaged intestinal lining is to do tests that may help to determine if an infectious agent may be contributing to the problem. The kinds of microorganisms that may do this include bacteria, fungi or yeast and parasites. Some of the bacteria that may be pathogenic are pylori, which primarily damages the lining of the stomach, leading to peptic ulcers, E. Coli, Klebsiella, anaerobic bacteria and many others. A comprehensive digestive stool analysis and culture may be useful to determine if there is an abnormal growth of one or more of these bacteria. Conventional physicians often do endoscopies and take biopsies of the stomach to see if pylori is present. However, a simple antibody blood test to Helicobacter pylori can also be useful.

Antibodies against Candida Albicans and/or a growth of this organism may help to establish that there is a Candida overgrowth. Predisposing factors to the development of an overgrowth of Candida include exposure to antibiotics, use of birth control pills, use of steroid medications and a high sugar diet. This organism may cause a variety of symptoms, such as bloating and gas, vaginitis and depressive symptoms.