When your stomach wall has been damaged too much to repair itself, it starts letting macro-molecules of food through the wall. This is simply because it's too damaged to heal quickly enough. It needs a break to be able to recover (Heal Autoimmune Disease by Fixing Diet).
This threshold is called the loss of oral tolerance. Before this threshold is reached, the intestinal wall can withstand being damaged on a minor level. This is a robust system ((Antifragile #citation)) (one that neither benefits from or is damaged by general chaos).
Once the threshold (Antifragile to a threshold) of the loss of oral tolerance has been reached, you officially have "leaky gut", officially known as pathogenic intestinal permeability.
Leaky gut is the number one thing to try and heal (Heal Autoimmune Disease by Fixing Diet) to reverse autoimmune responses. It's the macromolecules from food getting into the bloodstream that cause the chronic inflammation (Autoimmune symptoms are the weak link) which cascades into autoimmune.
#toolong