Gluten Intolerance: Significant effects and symptoms to be considered Gluten is a protein found in grains such as wheat, rye, and barley. If your body reacts to gluten, then it is considered gluten intolerant. This phenomenon is common, but it can sometimes have fatal consequences. Gluten intolerance occurs from three different causes. 1. Celiac disease 2. Nonceliac gluten sensitivity 3. Wheat allergy All three intolerances can present many different symptoms, some of which do not involve the digestive system. Taking a deeper look, we can see more symptoms of gluten intolerance that are seen with the following three causes: