It seems as if Leaky Gut or Intestinal Permeability is a very common occurence with all autoimmune diseases. Leaky Gut is caused when the walls of the intestines are compromised and holes in the intestines allow larger molecules of food that have not been properly digested to go in to the bloodstream. The body then sees these large molecules of foods as invaders and creates antibodies to them. Thus an allergy is formed. It is very common for people with autoimmune diseases to have several allergies, usually hidden until tested for.
One of the main reasons the intestine becomes compromised(develops gaps/holes) is candida yeast overgrowth. Other causes are drinking too much alcohol,taking too much aspirin/ibuprofen, lingering viruses, and not enough good bacteria in the gut(intestinal dysbiosis), drinking too much coffee with meals, and eating foods high in chemical additives. For more information on this see "Healing the New Childhood Epidemics..." by Kenneth Bock MD.
4 steps to follow for a lifetime:
1) Superior Nutrition 2)Supplement vitamins/minerals/nutrients you are missing 3)Detox your total body load(pesticides, chemicals, mercury etc.) 4) Medication if necessary(to combat yeast, bacterial infections etc.)
Your body's wellness goes in and out of balance throughout your lifetime, you need to follow these guidelines for life.