Gluten Contamination of Naturally Gluten-Free Grains and Flours

Reader Contribution by Wendy Gregory Kaho

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.

Contamination of Naturally Gluten-Free Grains and Flours

By Tricia Thompson, MS, RD

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

 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.

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.”

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

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

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.

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