Gluten is a protein, found in some food grains that are commonly eaten. These include primarily wheat, barley and rye.
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Gluten makes up about 85-90% of the protein in wheat, and is composed of roughly equal parts of gliadin and glutenins. These are rich in glutamine and proline, and are together called prolamines. While wheat or rye bread may be the most obvious source, gluten may also be present by cross-contamination in other foods, such as monosodium glutamate or soy sauce, ice cream and processed meat, or even gluten-free grains like oats.
This is because these products may be produced in a common manufacturing facility with wheat. Likewise, wheat flour may have been used to fill out the volume, improve the flavor, increase the protein content or add to the texture of these products.
Structure of gluten
Gluten has a unique structural protein, which forms a network when kneaded and brings about the stretchy quality of baked wheat products. These properties are referred to as the viscoelasticity of the final product and include elasticity, viscosity, extensibility, strength and cohesion of the dough.
Other proteins structurally similar to gluten are found as secalin, hordein, and avenins exist in other grains, such as rye, oats and barley. Gluten itself varies between various wheat genotypes, because of the possible combinations of various gliadins and glutenins, depending on where the wheat is grown, how it is milled, and the genetic makeup of the grain.
Gluten and autoimmunity
Gluten may trigger autoimmune-mediated gut inflammation called celiac disease in those with certain specific HLA types. This is caused by certain antigenic sequences of amino acids (epitopes) rich in proline and glutamine. These amino acids escape digestion in the gut and may enter the submucosal space below the gut lumen.
There they interact with the innate immune cells and T-lymphocytes and cause immunologic reactions. There are hundreds of immunogenic peptides, most commonly from α-gliadin, which differ in potency, and individual patients with celiac disease may react to only a few of them.
Whole grain wheat is a good source of protein and improves general health by lowering the risk of cardiovascular disease and diabetes. Gluten intolerance and celiac disease affect about 1% of the population each, therefore the majority of the population may not benefit from a gluten free diet. Gluten may also cause dermatitis herpetiformis, with or without celiac disease.
Some studies suggest also that gluten plays the role of a prebiotic and encourages the growth of beneficial bacteria, such as bifidobacterial in the colon, which prevents gut inflammation and colorectal cancer.
Wheat allergies and gluten
Wheat allergy is not the same as celiac disease, but it is the result of a usually temporary intolerance to one or more of the proteins in wheat. IgE tests positive and the symptoms include swelling and itching of the lips or mouth or even the throat, breathing difficulties, nausea and cramps or diarrhea, and in serious cases an anaphylactic reaction with vascular collapse. Most children with this condition outgrow it with time.
Overall, gluten is a normal part of the diet for most people and is health-promoting when ingested as part of a whole grain. A gluten-free diet would be advisable for the small minority who are intolerant or allergic to wheat or have celiac disease.