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. Some people are gluten-intolerant, which means 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.
