Your bowel is really just a long muscular tube, lined on the inside and criss crossed with blood vessels and nerve endings. The bowel wall is both a barrier and a filter; a barrier to all the substances in your gut that you do not want in your bloodstream; and a filter to let in valuable food and water molecules only.
The inside of your bowels looks rather like a shag-pile carpet covered with a thick layer of protective mucus. The technical name for the shag-pile carpet is villi. It greatly increases the amount of surface area available for absorption. The mucus is there to help the contents slide along, and also to protect the sensitive villi.
Although your stomach does the best it can to ensure that what enters your bowel is just food, sometimes nasties get through, like undigested protein molecules, bugs or parasites.
When you are under stress, production of this protective layer of mucus slows or stops, leaving your villi bare and unprotected. The front line cells are the epithelial cells that make up the outer layer of the villi. Although they are completely replaced every few days, they are sensitive.
Cells making up the villi are normally held together by special junctions. In your bowel these are tight junctions, reflecting the need to maintain an integral barrier. Selected food molecules are passed through the epithelial cells and everything else should remain within the bowel tube.
If something irritates or damages the epithelial cells, they become inflamed. Imagine for a moment when you last grazed your knee. The area became red and swollen almost immediately. This happened because blood vessels and other cells certainly moved apart to allow healing substances from your bloodstream into the wound area. When the inflammation and debris was cleared, the cells moved back into place again and the blood vessels sealed up.
A similar thing happens when your bowel wall is inflamed. The cells swell and move apart. Alas, by doing this, they are going to allow non food particles into your bloodstream, and set up a new immune reaction in your bloodstream. This is why its called leaky gut.
Your body may show signs of this in own own individual fashion; for some people its skin rashes, for others mood swings, or just feeling blah. Some people find their bowel motions are affected, some not.
You can now test whenever you have a leaky gut by asking your naturopath for an intestinal permeability functional pathology test. This will tell you scientifically whether you really do have a leaky gut, and if so, how serious it is.
To seal a leaky gut, you need to replenish that protective mucosal layer inside your bowel wall, and give the epithelial cells on the villi a chance to heal. The methods for achieving this depend on your symptoms, but treatment always includes stress management, and excludes any foods that you might be intolerant of. A treatment plan is always based on your individual symptoms.