What is intestinal permeability?
It has only fairly recently that practitioners have become increasingly aware that changes to gut permeability can have a dramatic effect on the health of the individual. The increased permeability of the intestinal mucosal barrier has shown to be associated with clinical disease manifested as infection, food allergies, Crohn’s disease, celiac disease, dermatological conditions such as eczema, ulcerative colitis, and auto-immune diseases such as rheumatoid arthritis, ankylosing spondylitis, Reiter’s syndrome, and other allergic disorders.
Decreased permeability appears as a fundamental cause of malnutrition, malabsorption and failure to thrive generally.
The small intestine function
The small intestine has the paradoxical function of being a digestive and absorptive organ as well as serving as a barrier to the penetration of toxic compounds and macro-molecules. The mucosal membranes accomplish this function through a combination of intestinal immune function and mechanical exclusion. Elaborate immunological and mechanical processes for excluding harmful dietary antigens, bacterial products and viable microbial organisms are present at the mucosal level.
How do we measure permeability?
It is easy to measure one’s intestinal permeability by way of simply measuring the passive permeability using a dual sugar technique utilising lactulose and mannitol.
The IP test may well be the most useful, precise and low-invasive way for assessing mucosal integrity in the small bowel. Mannitol (a monosaccharide) and lactulose (a disaccharide) are water soluble molecules that are not metabolised by the body. Mannitol is readily absorbed, and lactulose is only absorbed slightly.
The patient is given an oral dose containing 5gr of lactulose and 3gr of mannitol in a base of 10gr of glycerol. A timed urine sample is analysed and the ratios are assessed for the permeation of the water-soluble molecules (lactulose and mannitol) through the intestinal mucosa. Accurate information is obtained regarding gut integrity and function.
What do the results mean?
The permeation of the sugars through the intestinal mucosa can occur either through cells or between cells lining the small intestine wall. Small molecules (mannitol) readily penetrate cells and passively diffuse through them. Larger molecules (lactulose) normally are excluded by the cells in a normal, healthy functioning gut. The rate limiting barrier in this case is the “tight junction” between cells, which are only one layer thick. Tight junctions are important to maintain healthy epithelial integrity.
- Lactulose, being only slightly absorbed, serves as a marker for mucosal integrity.
- Mannitol is readily absorbed and serves as a marker for trans-cellular uptake.
- Low levels of mannitol and lactulose indicate malabsorption.Elevated levels of mannitol and lactulose indicate general increased permeability and are indicative of “leaky gut”syndrome.
- The lactulose/mannitol ratio is a useful parameter.
- Elevated ratios indicate that the effective pore size of the gut mucosa has increased, allowing access (to the body) of larger, and possibly antigenic molecules.