How is leaky gut syndrome diagnosed?

Leaky gut is a clinical diagnosis, and while there's no specific test that can tell you with 100% certainty that you have it, a positive Intestinal Permeability Test is strongly associated with the condition. This test measures the ability of two non-metabolized sugar molecules -- mannitol and lactulose -- to get through the digestive lining.

Mannitol is a small molecule that normally passes through easily and serves as a marker of how well nutrients are being absorbed. Lactulose is a larger molecule that doesn't normally pass through very well and serves as a marker for whether there are large holes in the lining. To perform the test, the patient mixes pre-measured amounts of lactulose and mannitol and drinks it. The test measures the amount of lactulose and mannitol recovered in a 6-hour urine sample.

Low levels of both mannitol and lactulose indicate malabsorption. Elevated levels of both lactulose and mannitol suggest general increased intestinal permeability, consistent with leaky gut. Permeability to lactulose may be increased, suggesting leaky gut, while permeability to mannitol may be decreased, suggesting malabsorption of small molecules.

The lactulose/mannitol ratio is a useful value; an elevated ratio indicates that the effective pore size of the gut lining has increased, allowing larger, possibly harmful molecules to gain access to the body.