Although wheat is chiefly made up of carbohydrates, and “low-carb” diets limit the use of wheat-derived foods like bread and pasta, there are in fact proteins in wheat. In genetically predisposed individuals, parts of these proteins provoke an abnormal reaction in the small intestine.
The key protein in wheat is called gluten, which is why celiac disease is also called gluten intolerance. Wheat grains are separated during milling into the outer husk (bran), the germ, and the “endosperm” which is white flour. There are four kinds of protein in the flour – minor albumins, globulins, glutenins and prolamins.
The albumins and globulins do not present a problem. The glutenins and prolamins do. Prolamin is the general term used for a specific part of the proteins that can be dissolved by alcohol. Each cereal grain has a different term for its prolamins, as follows:
- Wheat – gliadins
- Rye – secalins
- Barley – hordeins
- Oats – avenins
Gluten is the name given to the combination of gliadins (its prolamins) and glutenins found in wheat. These two proteins give wheat many of its characteristics. They are able to trap carbon dioxide, which helps wheat bread rise. The gliadins act as lubricants; they make it possible for the glutenins to slide over each other as the bread rises.
Gliadin (wheat prolamin) plus wheat glutenin = Gluten
People with celiac disease have trouble with parts of the protein found in wheat. The proteins are broken down during the digestive process, into small pieces, some of which trigger the abnormal response in the small intestine. All of troublesome proteins are rich in two specific amino acids called proline and glutamine. These amino acid building blocks make pieces of protein sticky. One particular piece of wheat gluten called alpha-gliadin is 33 amino acids long and does not get digested. This piece, which is called a peptide, as well as others that are similar in composition, triggers the abnormal response.
Wheat is in the grain subgroup called Triticeae, which in turn has two branches, the Triticinae and the Hordeinae. Wheat (triticum) and Rye (secale) are in Triticinae. Barley (hordeum) is in the Hordeinae group. Rye and barley have glutenins and prolamins so similar that they are just as bad as those from wheat.
Looking at all the grains, the Triticae belong to a larger group called the Festucoidaea, which contains the Aveneae, and Avena, which is oats. It also contains the Oryzeae, with Oryza, the name for rice. Rice is definitely different enough from the other grains to be safe for people with celiac disease to eat. Oats are more questionable.
Looking at the composition of the prolamins and glutenins in oats suggests that oats may be a safe grain. However, many people with celiac disease react to oats. This may be because there is some small amount of similarity in the proteins from the two grains. The other possibility is that oats can be contaminated by wheat, so that there is wheat gluten in oat flour and products.
Unless a grain processor, baker, or anyone else who handles flour keeps separate equipment for different grains, or are exceptionally careful to clean equipment after handling wheat, rye or barley and before handling oats, there is a danger of contamination.
It is not 100% certain that people with celiac disease react to oats because of cross contamination. It is possible that some are reacting to proteins in oats. There is ongoing research to try and answer that question. It is possible that different strains of oats may cause more or less reaction in the intestines of patients with CD, and that researchers will be able to find the safe oat strains.
It is always best to try and buy foods that are certified as gluten-free. Once you find a good place to buy grains and/or gluten-free breads, you should stick with what works. If you want to try oats, look for those processed safely away from wheat. If oats still give you symptoms, you have to avoid them.
There is an entire other branch of cereal grains that do not cause a reaction in people with celiac disease. These are the Pancoideae, and include corn, sorghum and millet. These grains along with a number of other gluten free grains are what you should be including in your gluten free diet.