It is one of the two peptides found in Gluten and must be restricted for patients with Celiac Disease or gluten sensitivity. Gluten is the storage protein found in wheat it is comprised of two smaller units glutenin and prolamines. In wheat it is Gliadin, Barley it is Hordein, Rye it is Secalin, and oats it is Avenin.
Oatmeal is often grown and / or processed near wheat making the chances of cross contamination high. It is possible to buy gluten-free oats where extra attention has gone into assuring there has not been any gluten contamination. Bob's Red Mill and Trader Joe's are two brands that have GF oatmeal.
According to the website of Freedom Foods, who make 'wheat free oats':"...all oats do contain gluten, but it's not that simple. See, oats naturally contain a type of gluten called Avenin that is different to the type of gluten you find in wheat, rye, barley and triticale.Now if you talk to the Coeliac Society of Australia, they say about 4 in 5 people with Coeliac Disease can tolerate oats. We say the easiest thing to do is read the Coeliac Society position statement on oats and seek medical advice on whether this applies to you."The safety of oats for patients with celiac disease depends on the variety of oat - some are more toxic than others. The method used to assess this can be applied to other foods to determine their toxicity as well.Oats do not contain gluten, the problem is most oats are cut on the same mill as other grains that do. Unless it states gluten free on the oatmeal or regular cut oats stay away.