It's likely (but not certain) that you can.
There are two potential problems with oats. The first is that oats are almost always cross-contaminated with the gluten grains wheat, barley and rye, since they're all grown in the same fields and harvested, stored and processed with the same equipment. That makes it impossible to tell if you're reacting to the oats themselves or to the gluten cross-contamination in the oats.
You can solve that problem by purchasing only pure oats grown to be free of that cross-contamination (my article Is Oatmeal Gluten-Free? contains some recommendations for safe oat and oatmeal sources).
That brings us to the second potential problem: some people react to oats even pure, gluten-free oats the same way they do to gluten grains.
Pure oats don't contain the gluten protein that's responsible for reactions in people with celiac disease and non-celiac gluten sensitivity. But oats are a close relative of wheat, barley and rye, and they contain a somewhat similar protein called avenin.
Many people with celiac disease can eat oats with no problem, though a small-but-not-insignificant percentage possibly in the range of 10 to 15 percent also react to avenin.
So don't rush out and start gorging on oatmeal cookies just yet: experts urge you to check with your doctor before introducing oats (your doctor likely won't want you to try oats unless you're doing well on the gluten-free diet already), and to start very slowly. I've seen recommendations for trying a tablespoon or two of pure gluten-free oatmeal at first, just to see how you do before you add more.
If you seem to tolerate the oats well, you can increase the amount. The Celiac Sprue Association advises limiting your oat consumption to about 1/2 cup dry oats per day, while the Canadian Celiac Association recommends a slightly larger maximum amount up to 3/4 cups. (Note that 3/4 cups of dry oats will make a lot of oatmeal!)
I have non-celiac gluten sensitivity; can I eat oats safely?
Unfortunately, that's not as clear. There just hasn't been any medical research yet on whether people with non-celiac gluten sensitivity react to oats or not.
Anecdotally, it's a mixed bag: some people with gluten sensitivity say they can eat oats just fine, while others say oats make them just as sick as gluten does. So if you have gluten sensitivity, the only way to know if you react to oats or not is to try them and see if you get sick.
Just as with people who have celiac disease, you should start with very small amounts of pure gluten-free oats and build up slowly, watching all the time for your typical glutening symptoms.
I've heard some varieties of oats are less toxic than others. Is that true?
There's some new research that hints at this.
A 2011 Spanish study looked at how components of the immune system, called monoclonal antibodies, reacted to the different oat varieties.
The study found that different oat varieties fall into three groups: significant reactivity with monoclonal antibodies (potentially indicating an immune system reaction akin to a gluten reaction), slight reactivity (potentially indicating a weaker but still noticeable immune system reaction), and no detectable reactivity.
"These differences may explain the different clinical responses [to oats] observed in patients suffering from celiac disease and open up a means to identify immunoloigcally safe oat cultivars, which could be used to enrich a gluten-free diet," the authors concluded.
And an Italian study used cell samples from people with celiac to see how those cells reacted to different oat varieties in test tubes. The study concluded that two oat varieties Avena genziana and Avena potenza didn't provoke major celiac-specific immune system reactions, at least in the test tube. But the researchers cautioned that both oat varieties did seem to cause some low-level immune system changes in the cell samples.
Research on all of this is ongoing, but it's too early to single out particular oat varieties as safer or less safe for us to eat.
So what's the bottom line Should I eat oats or not?
That's a question only you can answer (in conjunction with your doctor). As I said, studies show most people with celiac disease can eat relatively small quantities of oats safely, and anecdotal evidence indicates the same may be true for people with non-celiac gluten sensitivity.
If you do decide to introduce oats, make sure to buy only pure gluten-free oats, and don't overdo it while you're still determining how your body reacts.
Celiac Sprue Association fact sheet. Guide to Oats. Accessed March 2, 2013.
Comino I et al. Diversity in oat potential immunogenicity: basis for the selection of oat varieties with no toxicity in coeliac disease. Gut. 2011 Jul;60(7):915-22. doi: 10.1136/gut.2010.225268. Epub 2011 Feb 12.
Maglio M et al. Immunogenicity of two oat varieties, in relation to their safety for celiac patients. Scandanavian Journal of Gastroenterology. 2011 Oct;46(10):1194-205. doi: 10.3109/00365521.2011.603159. Epub 2011 Aug 15.
Pulido OM et al. Introduction of oats in the diet of individuals with celiac disease: a systematic review. Advances in Food and Nutrition Research. 2009;57:235-85. doi: 10.1016/S1043-4526(09)57006-4.
Rashid M et al. Consumption of pure oats by individuals with celiac disease: a position statement by the Canadian Celiac Association. Canadian Journal of Gastroenterology. 2007 Oct;21(10):649-51.
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