Our gastrointestinal (GI) tract is considered to be outside the body. In fact the the mucous membranes lining our GI tract represent the largest surface area of the body exposed to the external environment and all it contains, including microorganisms and toxins. The job of the mucous membrane lining the small intestine is to absorb fully digested nutrients - the macronutrients (sugars, amino acids, fatty acids) and the micronutrients (vitamins, minerals, and others) - while ensuring undesirable microoganisms, toxins, allergens, and partially digested foods are prevented from entering the body. In health this is achieved by the cells that make up the mucous membranes letting only small molecules pass through them and being tightly packed together to form what are known as 'tight junctions'. Properly functioning tight junctions prevent the contents of the GI tract entering the body by passing through the gaps between cells. Unfortunately various substances including alcohol, medications (e.g. painkillers), food allergens, pathogenic microorganisms (bacteria, yeast/fungi, parasites, viruses), and various toxins produced by these microorganisms or otherwise ingested can cause inflammation of, and damage to, the mucous membranes of the small intestine, and upset this delicate system of absorption and protection. This can result in malabsorption of nutrients and nutrient deficiencies as well as increased passage of toxins, pathogens, and allergens into the body (leaky gut syndrome). Abnormal intestinal permeability has been linked to numerous diseases including food allergies, autoimmune diseases, celiac disease, liver disease, irritable bowel syndrome, and chronic fatigue syndrome. It may also explain symptoms in cases where a diagnosis has not been forthcoming from conventional medical testing.
Details of the Intestinal Permeability Test
The test generally involves collecting a single urine sample then consuming a solution that contains mannitol and lactulose (or alternatives) and then collecting all the urine you pass for a number of hours following this. You then take a smaller sample from this and send it along with the initial sample back to the lab in a prepaid envelope. You are usually instructed to fast for a certain period prior to a during the test period to avoid distorting the results.
Mannitol is a sugar alcohol and is a small molecule that is usually absorbed through the cells of the small intestine. If abnormally low amounts of mannitol are found in your urine sample following consumption of the mannitol/lactulose solution this indicates malabsorption and further testing would be required to find out why. If elevated mannitol is found this indicates general increased intestinal permeability, or leaky gut. Lactulose is a sugar that is not usually absorbed from the GI tract so there should be little lactulose found in your urine sample following its consumption. If it is elevated this is a strong sign of leaky gut syndrome. Lactulose cannot be absorbed through the cells of the small intestine so this result demonstrates damage to the intesinal lining resulting in tight junction malfunction and widening of the gaps between cells. The lactulose actually passes into the body through these large gaps.