Gluten is found in grains, but not all grains contain the type of gluten that is known to cause digestive issues for people with celiac disease. According to the Federal Register, when referring to gluten or gluten-free diets, the medical establishment is referring to the type of gluten found in wheat and grains that have gluten similar to wheat gluten. Most people on a gluten-free diet can still enjoy grains such as buckwheat, rice, millet and quinoa.
Wheat
Wheat and its many derivative forms contain gluten. Some of these forms are obvious, such as wheat germ, wheat flour and wheat bran. The National Institute of Diabetes and Digestive and Kidney Diseases points out there are several forms of wheat that don't include the word "wheat" in them, including graham flour, semolina, farina and durum. Wheat appears in most baked goods, many processed foods and most pastas. Even if a food does not have gluten-containing ingredients listed, it may still have trace amounts of gluten if it is prepared in the same place as other foods that contain gluten. Look for foods labeled as "gluten-free" to ensure they do not contain wheat, wheat byproducts or any other grains that contain gluten and are prepared in a gluten-free environment.
Barley
Barley is another grain that contains gluten. Barley is also used to make beer, ale and lager, so you should avoid these alcoholic beverages or those like them. There are several foods you might not suspect would have barley, but read the product label carefully, as barley malt extract is often used as flavoring agent for chips, cereals, bouillons and some beverages. If you are on a gluten-free diet, a good rule of thumb is to avoid any processed foods that you are not 100 percent certain are gluten-free.
Rye
Like barley, rye is close in composition to wheat and contains the same kind of harmful glutens for people who are gluten-intolerant. Unlike barley, rye is not often used as a flavoring agent, and, unlike wheat, it is not often used as a thickening agent. This makes it a little easier to avoid, since most products that contain rye, such as rye crackers or rye bread, will be obvious. You should still check the ingredients list on foods to ensure they don't contain rye or a rye/barley hybrid known as triticale, reports the NYU Langone Medical Center.
