What exactly is gluten?

Protein in grains.: Gluten is a protein composite found in wheat, barley, & rye. Worldwide, gluten is a source of protein, & is often used as an additive to foods low in protein. Celiac disease, is an allergy-like sensitivity to gluten, & patients must avoid gluten or suffer the effects. Currently, it is fashionable to choose 'gluten-free' foods, even without celiac disease, but the benefits are questionable.