Gluten proteins consist of the soluble gliadins (α, γ, and ω) and the insoluble glutenins. Each gluten protein type consists or two or three different structural domains; one of them contains unique repetitive sequences rich in glutamine and proline.
Gluten proteins are found in grains like wheat, barley, and rye, commonly in foods like bread, baked goods, crackers, pasta, cereals. Surprising foods that may contain gluten includes caramels, licorice, soy sauce, salad dressings.
For people with celiac disease (1% of population), gluten is toxic even at concentrations as little as 50 mg per day - or one fresh breadcrumb. For those with non-celiac gluten intolerance (common in allergic patients), slightly higher levels can be consumed. Common symptoms of Non-celiac gluten sensitivity (NCGS) are mental fatigue ("brain fog"), lack of energy or lethargy, gas, bloating, abdominal pain or cramps, diarrhea and even constipation. At this time it is unclear if gluten is the cause of NCGS or if it might be a reaction to a specific sugar or chemical component found in wheat. For everybody else, eating reasonable amounts of gluten would diversify their diets and help to maintain populations of beneficial bacteria supporting immune system.