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.

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Comments (4)

  • Salman ahmad Reply


    February 27, 2018 at 1:43 am
  • Victor Vicini Reply

    Hi Tricia,
    Love your site!

    I have a question about the study of grains and the amount gluten contained. I like to mill my own grains like buckwheat, brown Rice and amaranth. Do you have a study that reflects the ppm for grains in their pure state and NOT processed and sold as ‘flour’? Just wondering if the ppm would be reduced if the milling was not commercially.

    Thank you

    March 17, 2019 at 1:12 pm
    • Tricia Thompson Reply

      Hi Victor, It is my very strong recommendation that all naturally gluten-free grains and pseudocereals eaten by someone with celiac disease should be labeled gluten-free. GIPSA standards allow a certain percentage of foreign material in grains with standards. Naturally gluten-free grain may come into contact with gluten-containing grain at any point from the field to the processing plant/mill. Grinding your own grain will prevent any additional cross contact but it is a good idea to purchase labeled gluten-free grain and pick through it before grinding to remove any foreign material.

      March 21, 2019 at 5:09 pm
  • Maya Reply

    I am really shocked at how bad the soy flour contamination is! Soy isn’t really a grain or pseudocereal, but a legume. I wonder how and where in the processing it gets so contaminated. I would never think to look for gluten free labeling as I was told to only seek it out for grains and pseudocereals. As someone newly diagnosed, this is really disturbing and makes me feel like nothing can be trusted.

    September 13, 2019 at 2:56 pm

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