Zonulin is a protein molecule that modulates the opening and closing of tight junctions between cells of the wall of the digestive tract, allowing nutrients to pass in and out of the intestines. When too much zonulin is produced, the tight junctions between the cells of the gut lining open up too much, creating a situation known as leaky gut. Two triggers for the release of zonulin are the consumption of gliadin and gluten (found in certain grains).
Healthcare practitioners can find out more about zonulin and leaky gut on our sister site, Probiotic Professionals.