Nutrient uptake through the enterocyte cells, along with that through the gap junctions is regulated by chemicals called proteases. More than 20 proteases are known to affect permeability for nutrition uptake. Proteases can be secreted by the body cells (e.g., pancreatic proteases) to assist greater volumes of nutrition to pass into the body by stimulating the enterocyte cells to "open" the gap-junctions after eating meals. Protease release by enterocyte cells can also be triggered by invading gut bacteria such as E. coli and Salmonella typhi, as well as toxic food lectins passing through the gut. This can cause gut diseases by damaging the mucous protective layer and also altering the efficient functioning of the gap-junctions.
Zonulin is one of the proteases that open gap-junctions. It does this by unraveling the adhesive proteins joining the enterocyte cells. Limited amounts of zonulin are normally excreated by enterocyte cells to temporarily increase intestinal permeability at specific gut locations for quicker uptake of any available nutrition. For example, as sugars pass through the gut they can be more quickly absorbed for energy bursts, by temporarily opening the gap junctions to boost through-the-cell absorption.
While zonulin production is normally a regulated occurrence, if it is be continuously stimulated by bacteria or food lectins, then gap-junctions across a region of the gut will become permanently "leaky". This will allow unwanted pathogens and chemicals to enter the body proper. However, invading gut bacteria have to reach a certain population size to stimulate enough zonulin production to effectively open-up reasonable areas of the gut barrier to effectively invade the body. A competent immune system normally prevents this.
If the immune system is competent and is effectively monitoring gut bacterial populations and food lectin activity in the gut, it is able to act precisely when these actually attempt to enter through the gap-junctions. A competent immune system will mount a quick attack—not too strong to damage the enterocyte cells, and not too weak to allow infection or poisoning to occur within the body proper. If it is competent it will use the right amount of water pressure through the lymph system to back-flush the bacteria and the food lectins out into the gastrointestinal tract through the gap-junctions, instead of resorting to inflammatory cytokines. This adequate response would only produce slightly loose stools on occasion with no pain nor abdominal swelling.
If the immune system is incompetent, has communication scarring, or cannot "read" the bacterial/lectin threat, it will mount a late-stage defence and overreact by resorting to the use of inflammatory cytokines through T-cells (which record inappropriate memories to the events). T-cell aggression will always produce collateral damage to the local epithelial cells and create large holes in the gastrointestinal barrier that may take days to heal (but only if the T-cells stop their reaction).
Depending on the individual person's immune system coding of these T-cells, the T-cells can remain within the gastrointestinal tract having their "memory" triggered again and again by plant lectins to cause more destruction of the gut wall as an autoimmune response. Or they can migrate to different organs to cause other types of cell destruction as a different autoimmune disease.
An incompetient immune system will also overreact in its use of water pressure to attempt to back-flush the bacteria and chemicals through the gap-junctions or holes, into the gastrointestinal tract. This will cause chronic watery stools, abdominal bloating (the "beer-gut") and intense abdominal pain, with loss of weight.
"Wasting Disease" is a name that was used for centuries in Europe before the term coeliac disease was coined. An "old wives' tail" suggested that bread was behind "Wasting Disease". Science eventualluy confirmed this, in research conducted in Holland after the second world war by the Dutch pediatrician, Willem K. Dicke.
If the enterocyte cells are exposed to ongoing bacterial attacks, or the person continually consumes the particular plant food with the zonulin-stimulating lectins, a vicious cycle of chronic "full-on" gut leakage with ongoing collateral cell damage can occur. This is the most common cause of gut autoimmune diseases such as ulcerative colitis, coeliac disease or Crohn's disease, which eventually leads to the various colon cancers.
All plant foods have lectins that have the potential to stimulate zonulin production. The lectins are different for the different plants. Plants with lectins that can be denatured by normal cooking are safe to eat. Plants with lectins that are broken down by digestive enzymes are safe to eat. However lectins that are not denatured by these processes, and are biologically intact when they move into the small and large intestines, have the potential to contribute to leaky gut disease.
The most studied of the lectin-containing foods that cause leaky gut disease across the human population, are the gluten-containing grains such as wheat, barley and rye—they contain gluten. When gluten comes into contact with human enterocyte cells, it stimulates ongoing zonulin release for quite a long period (days to weeks).
Everyone eventually suffers degrees of this disease. Some die from it and some just experience low grade symptoms. Gluten predominantly, as well as other plant lectins, in combination with inappropriate bacteria living in the gastrointestinal tract, cause leaky gut disease and are the triggers for the various gastrointestinal tract autoimmune diseases.