Gluten is a protein found in grains such as wheat, barley, and rye. It can be found in your classic breads, cereals, pasta, and beer, and even the not so obvious products like soy sauce, vitamin supplements, and toothpaste. (Source) People with Celiac disease or gluten sensitivity can’t tolerate these foods, and ingestion will often lead to varying degrees of inflammation of the intestinal tract, abdominal pain, bloating, diarrhea, constipation, “foggy brain,” rash or headache. (Source)