Zonulin is a chemical that is release when the gut becomes inflamed and porous. Think of your bowel like a long tube made of square or rectangular blocks. These blocks fit tight so not to allow food particles outside of the bowel. What happens when you sprain your ankle? It swells. The same thing happens with your gut except the square blocks now swell and more closely resemble beach balls. Now try to build an impermeable wall with beach balls! You can’t. There are too many gaps in a wall made of spheres. This is where the concept of leaky gut comes from.