Gluten Contamination of Naturally Gluten-Free Grains and Flours


I've asked registered dietitian, Tricia Thompson, to join me today to share the results of a study she and her colleagues published that changed the way many of us in the gluten-free community think about gluten-free grains and where we buy them.

Gluten Contamination of Naturally Gluten-Free Grains and Flours 

By Tricia Thompson, MS, RD

 My colleagues Anne Lee, Thomas Grace, and I recently published the results of our pilot study on gluten contamination of naturally gluten-free grains, seeds, and flours in the United States (J Am Diet Assoc. 2010;110:937-940). While we have known for some time that commercially available oats are frequently contaminated with gluten there is little published information on gluten contamination of other naturally gluten-free grains. The question we hoped to answer with our study was whether oats are unique in their propensity for contamination or are other grains also at risk?

 For those of you who may not be so familiar with the gluten-free diet, individuals with celiac disease must avoid gluten, a protein found in wheat, barley, and rye. In place of these grains, naturally gluten-free grains are used, including corn, rice, millet, teff, sorghum, wild rice, amaranth, buckwheat, and quinoa. Most people with celiac disease also can tolerate oats but they have to be labeled gluten free. This is because oats may become contaminated with wheat, barley, and rye while being grown, harvested, transported, and processed.  

 We tested 22 naturally gluten-free grains, flours, and seeds NOT labeled gluten free for gluten contamination. Fifteen of the products tested would be considered gluten free under the Food and Drug Administration’s proposed rule for the labeling of food as gluten free. This proposed rule states that labeled gluten-free food must contain less than 20 parts per million of gluten. The remaining 7 products contained from 25 to 2,925 parts per million of gluten.

 Products containing greater than or equal to 20 parts per million of gluten included 2 samples of millet flour; 1 sample of millet grain, buckwheat flour, sorghum flour, and 2 samples of soy flour.

 Products containing below 20 parts per million of gluten included 1 sample of millet grain; white rice flour; basmati rice; long grain brown rice; enriched corn meal; instant polenta; 1 sample of rice flour; hulled buckwheat; buckwheat groats; amaranth flour; flax seed; and amaranth seed.

 The results of this study suggest that “some inherently gluten-free grains, seeds, and flours not labeled gluten-free are contaminated with gluten. This potential risk of contamination is a health concern for people with celiac disease, who must follow a gluten-free diet. The consumption of these products can lead to inadvertent gluten intake.”

 It is very important to stress that this study was not large enough to make any generalizations about the specific grains, seeds, and flours more or less likely to be contaminated with gluten.

Bottom Line Recommendation: Whenever possible chose naturally gluten-free grains, flours, seeds, and products made from them that are labeled gluten free. While a gluten-free label is not a guarantee that products have been tested and contain below 20 parts per million of gluten, they are still more likely than unlabeled products to have been tested. It also is recommended that you contact manufacturers of labeled gluten-free products and ask them what steps they are taking to make sure their products are gluten free.

 For more information on this study and steps you can take to make sure the products you eat are gluten free, please see the articles 

   I also have started a new website that is currently available for preview. This site is dedicated to making state-of-the-art gluten-free food testing date available to consumers.


Thanks to Tricia for this eye-opening study. I've always wondered why oats were suspect, but never the corn or soy beans I see rotated each year on the farms surrounding me in rural Ohio. They use the same equipment and storage for all three crops and I thought that must be the same for other gluten-free grains. I share some of my concerns about the contamination of gluten-free grains in the local food movement on my Celiacs in the House blog.


Wendy Gregory Kaho
4/18/2011 4:37:37 PM

That's why I was so pleased when Tricia said yes to my guest post request. She really has taken this on in a big way and those of us who need to avoid gluten are safer because of Tricia and her colleagues.

Cheryl Harris
4/18/2011 3:00:12 PM

thanks for covering such a wonderful topic, Tricia and Wendy! It's such an important one, and Tricia has really been a pioneer in getting us concrete evidence to let us know where we stand.

Subscribe Today - Pay Now & Save 64% Off the Cover Price

50 Years of Money-Saving Tips!

Mother Earth NewsAt MOTHER EARTH NEWS for 50 years and counting, we are dedicated to conserving our planet's natural resources while helping you conserve your financial resources. You'll find tips for slashing heating bills, growing fresh, natural produce at home, and more. That's why we want you to save money and trees by subscribing through our earth-friendly automatic renewal savings plan. By paying with a credit card, you save an additional $5 and get 6 issues of MOTHER EARTH NEWS for only $12.95 (USA only).

You may also use the Bill Me option and pay $17.95 for 6 issues.

Canadian Subscribers - Click Here
International Subscribers - Click Here
Canadian subscriptions: 1 year (includes postage & GST).

Facebook Pinterest Instagram YouTube Twitter flipboard

Free Product Information Classifieds Newsletters