Since posting the summary of the article, “Gluten Contamination of Grains, Seeds, and Flours in the United States: A Pilot Study,” many concerned gluten-free consumers have contacted me asking “now what?”

Important points to keep in mind about the study:

1.We tested grains, flours, and seeds that were NOT labeled gluten-free. One of the major goals of this research was to determine whether grains other than oats are contaminated with gluten.

2.Under the proposed FDA rule for labeling of gluten-free foods, inherently gluten-free single ingredient foods like grains can be labeled gluten-free but they also have to state on the label that all foods of that type are gluten-free. In other words, a gluten-free manufacturer of millet could label the product gluten-free but they would also have to state something along the lines of, “all millet is gluten-free.”

3.Oats are the one exception to the above rule. This is because we have research showing they are contaminated. See Tricia Thompson. Gluten Contamination of Oat Products in the United States. New England Journal of Medicine 2004;351:2021-2022.

4.We did not test labeled gluten-free grains, flours, and seeds. The point of this research was not to determine whether manufacturers of gluten-free foods test their products for gluten.

5.We also wanted to determine whether voluntary allergen advisory labeling can be used to determine the likelihood that a particular product is contaminated with gluten (based on our findings, it can’t).

Should you continue to eat gluten-free grains?


There is absolutely no reason to stop eating naturally gluten-free grains and flours that are labeled gluten-free. These grains, especially whole grain varieties, such as brown rice, whole corn, amaranth, buckwheat, quinoa, teff, millet, sorghum, and wild rice are exceedingly healthy and an important part of your diet. Keep in mind that gluten-free diets as typically followed in the US are low in fiber, B-vitamins, and iron all of which are provided by these grains.

BUT you ask, “How do I make sure the grains I buy are gluten free?”

My personal recommendations:

1.Purchase only those gluten-free grains and flours that are labeled gluten-free. Labeled gluten-free varieties of these foods may be more expensive but there is a reason for this—you are paying for all the extra steps manufacturers must take to ensure their products are not cross contaminated.

2.Contact manufacturers of labeled gluten-free products and ask them about the steps they take to ensure their products are gluten-free (see specific questions to ask below). If a manufacturer is not forthcoming, this to me is an indication that I probably want to avoid their products.

3.Whenever possible purchase grain-based foods, such as rice noodles that are labeled gluten-free.

4.When a manufacturer has a gluten-free line but they don’t include a particular product in that line even though it appears to be gluten-free based on ingredients, there is a reason—trust them!

5.Stay clear of grain foods that are not specifically labeled “gluten-free” but instead have vague labeling such as, “made with gluten-free ingredients” or “no gluten ingredients used.” This is a red flag (to me at least) that the manufacturer does not test for gluten contamination.

6.Last but not least, remember that manufacturers are learning right along with the rest of us.

Questions to ask manufacturers

I have posted these questions before but this seems like a good time to repeat them.

1.What type of facility do you use? The first thing that many consumers want to know is whether gluten-free food is produced in a dedicated facility.

If it isn’t, ask whether the manufacturer has dedicated production times, uses dedicated equipment, or has scrupulous cleaning standards. Also ask if they have a Hazard Analysis Critical Control Point (HACCP) or Allergen Control Program (ACP) in place.

2.Do you test your at-risk “raw” ingredients for gluten and how frequently do you test? It is important to keep in mind that just because a gluten-free food was made in a dedicated facility, doesn’t mean all ingredients used to make that product were produced in a dedicated facility. A gluten-free food can only be as “clean” as the ingredients used to make it. This is why it is important that manufacturers have a Certificate of Analysis (that includes gluten) from ingredient vendors and test the ingredients they use in their products for gluten, especially those that are most at-risk for contamination, such as grains, flours, and starches.

3.Have you validated your in-house testing procedure? According to Thomas Grace, CEO of Bia Diagnostics “while quick easy methods (e.g., lateral-flow device, dipsticks, quick or fast ELISAs) can be used for surface screening and/or verification of Certificate of Analysis from vendors ALL methods should be validated before they are employed in a Hazard Analysis Critical Control Points (HACCP) or Allergen Control Programs (ACP).

“Validation usually would consist of taking an ingredient, ingredient mix, and/or finished product negative control and running the test on the sample. If the test is negative, you would then take the samples or sample mixes and add a 20 part per million gluten spike (a proportional mix of wheat gliadin, barley, and rye) into each sample (the gluten spike should be less than 10% of ingredient) and run the test again to be sure you get a positive result for each of the spiked samples.”

“If all samples are positive at the level expected, take pure wheat flour (if using “dip-stick method”) and test it to be sure you don’t get false negative results with an over abundance of contaminant. Also, finished products should be periodically checked (every batch if produced on shared equipment or every few months if not) via third party labs using CODEX/AOACRI approved methods.”

4.Do you periodically send your finished product to a third-party lab for testing using the R5 ELISA? While gluten testing is important, it must be understood that all tests are not equal — some are better than others.

Two sandwich ELISA tests are frequently used in the United States — the R5 ELISA and the omega-gliadin ELISA. Under current Codex standards the R5 ELISA has been endorsed for gluten analysis. In the Food and Drug Administration’s proposed rule for labeling of foods as gluten-free, the R5 ELISA is being considered for gluten determination.

Neither of these assays is perfect but the R5 ELISA is widely considered to be state-of-the-art. Among other drawbacks, the omega-gliadin ELISA does not accurately assess for barley contamination.

It is important to ask manufacturers what assay they are using to assess gluten and what level of gluten they consider gluten-free. No food should be labeled gluten-free if it contains 20 parts per million or more gluten. In my opinion, it is very important that manufacturers use the R5 ELISA (the regular and not the fast test) and not the omega-gliadin ELISA to test their final product. It addition, it also is important that manufacturers test their highly hydrolyzed products using the competitive R5 ELISA.

Prior to his passing, I co-authored a paper with Dr. Enrique Mendez on the various assays to assess gluten content (Commercial assays to assess gluten content of gluten-free foods: why they are not created equal. J Am Diet Assoc. 2008 Oct;108(10):1682-7). If you would like more information about this article, please contact me through my website

Hopefully some of your questions have been answered and concerns addressed. If not, let me know!

Copyright ©  by Tricia Thompson, MS, RD

Also available at:

Contamination of naturally gluten-free grains: part 2