Gluten refers to the proteins found in wheat endosperm (a type of tissue produced in seeds that's ground to make flour). Gluten both nourishes plant embryos during germination and later affects the elasticity of dough, which in turn affects the chewiness of baked wheat products.
Gluten is actually composed of two different proteins: gliadin (a prolamin protein) and glutenin (a glutelin protein).
Though "true gluten" is sometimes defined as being specific to wheat, gluten is often said to be part of other cereal grains — including rye, barley and various crossbreeds — because these grains also contain protein composites made from prolamins and glutelins.
Some people are gluten-intolerant, meaning their bodies produce an abnormal immune response when it breaks down gluten from wheat and related grains during digestion.
The most well-known form of gluten intolerance is celiac disease, which affects one in every 141 people in the United States, according to the National Institutes of Health. When someone with celiac disease consumes gluten, it triggers an immune response that damages their intestines, preventing them from absorbing vital nutrients.
Wheat allergy is a rare type of gluten intolerance — it's a classic food allergy marked by skin, respiratory or gastrointestinal reactions to wheat allergens.
Recently, scientists have become aware of another potential form of intolerance called nonceliac gluten sensitivity. After consuming gluten, patients with gluten sensitivity may experience many celiac disease symptoms, such as diarrhea, fatigue and joint pain, but don't appear to have damaged intestines.
In cases of gluten intolerance, doctors typically recommend a gluten-free diet. Patients must avoid eating any foods and ingredients that contains gluten, including bread, beer, french fries, pasta, salad dressing, soy sauce and even some soups (unless otherwise marked as "gluten-free").
In recent years, many people without gluten intolerance have taken up gluten-free diets. Experts worry, however, that going on these diets without explicitly needing to could be detrimental to a person's health, as gluten-free foods are often nutrient-deficient.