Naturally Gluten-Free Grains and Gluten Contamination

Naturally Gluten-Free Grains and Gluten Contamination

We all know that if we eat oats they should be labeled gluten-free. We know this because it is well established that “regular” commercial oats are very likely contaminated with gluten. If you are interested in testing data it is available here.

What is less well established is whether other naturally gluten-free grains NOT labeled gluten-free like millet, sorghum, and buckwheat are likely contaminated too.

In 2010, Thomas Grace, Anne Lee and I published the study, “Gluten contamination of grains, seeds, and flours in the United States: a pilot study.” We tested twenty-two single ingredient naturally gluten-free grains, seeds, and flours NOT labeled gluten-free. Thirteen (59%) contained less than 5 parts per million of gluten; nine (41%) contained gluten in the range of 8.5 to 2,925.0 parts per million of gluten.

We concluded that “the findings of the current study indicate 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.” The abstract of this study is available here.

So how does the gluten content of labeled gluten-free flours compare to those not labeled gluten-free?

Labeled Gluten-Free Flours (mean of 6 extractions)
Data from Gluten Free Watchdog

Buckwheat flour: < 5 ppm gluten
Millet flour: 15.5 ppm gluten
Rice flour (brown): < 5 ppm gluten
Sorghum flour: < 5 ppm gluten (1 extraction tested at 7 ppm gluten)
Soy flour: < 5 ppm gluten (1 extraction tested at 6 ppm gluten)

Gluten-Free Flours NOT Labeled Gluten-Free (mean of 2 extractions)
Data from grain contamination study

Buckwheat flour: 65 ppm gluten
Millet flour brand A: 305 ppm gluten
Millet flour brand B: 327 ppm gluten
Rice flour (white) brand A: 8.5 ppm gluten
Rice flour (white) brand B: < 5 ppm gluten
Sorghum flour: 234 ppm gluten
Soy flour brand A: 2,925 ppm gluten
Soy flour brand B: 92 ppm gluten

More data on the gluten content of both labeled and not labeled gluten-free flours certainly would be helpful before drawing conclusions. BUT because of the risk of cross-contamination it is my recommendation (and the recommendation published in the American Dietetic Association’s Celiac Disease Toolkit) that you buy naturally gluten-free grains and flours that are labeled gluten-free.

Because of cross-contamination risks it is very important that manufacturers of labeled gluten-free foods make sure that either they or their suppliers routinely test all grains and flours used in their products for gluten contamination.

It also is important for manufacturers to test products using an assay that utilizes the R5 antibody. Some assays still utilize the omega-gliadin antibody. These assays severely underestimate gluten contamination from barley.

If you have any questions, please feel free to contact me.

©Copyright 2011 by Tricia Thompson, MS, RD for Gluten Free Watchdog, LLC ( All rights reserved. No part of this article may be reproduced without the prior written permission of Tricia Thompson.

Share this post

Comment (1)

Leave a Reply

Your email address will not be published. Required fields are marked *