Gluten Contamination in Labeled Gluten-Free Foods

Gluten Contamination in Labeled Gluten-Free Foods

Gluten Contamination in Labeled Gluten-Free Foods

The good news: Three studies on gluten contamination in labeled gluten-free foods have been published in the past few weeks.

The bad news: The findings are wildly different.


Study One:

Girdhari M. Sharma, Marion Pereira, Kristina M. Williams. Gluten detection in foods available in the United States – A market Survey. Food Chemistry 169 (2015) 120–126. (Published online ahead of print)

Note: Study authors are from the Food and Drug Administration.

Number of labeled gluten-free foods tested: 275; Food purchased from local grocery stores.

Categories of foods tested: grains, seeds, nuts, legumes, condiments, sauces, curry, soup, soup mixes, baking mixes, baked foods, pasta products, breakfast cereals, snack foods, granola, bars, energy bars, beverages, ice cream, frozen dessert, meat, meat substitute, refrigerated or frozen foods, other.

Assay used: Ridascreen Gliadin R5 Sandwich ELISA (R7001) with cocktail extraction solution and the Morinaga wheat protein sandwich ELISA.

Results: Reported as average of four readings (combining results from both assays)

  • 3 samples (1.1%) of tested foods had gluten levels greater than 20 ppm of gluten.


Study 2:

Hyun Jung Lee, Zach Anderson, and Dojin Ryu. Gluten Contamination in Foods Labeled as ‘‘Gluten Free” in the United States. Journal of Food Protection, Vol. 77, No. 10, 2014, Pages 1830–1833.

Note: Study was supported in part by a grant from the United States Department of Agriculture.

Number of labeled gluten-free foods tested: 78; Food randomly collected from local markets in Moscow, Idaho in May 2013.

Categories of foods tested: breakfast cereal, pasta, bread, tortilla, nutrition bar, snack food, baking mix.

Assay used: It is not clear from the article which assay and extraction solution was used. I have reached out to the corresponding author for clarification. This post will be updated when this information is available.

UPDATE: I have been in communication with the study authors. The corresponding author states that the foods were assessed for gluten content using the R7021 assay which is the COMPETITIVE R5 ELISA. This assay is used to assess gluten in hydrolyzed and fermented foods (eg, beer, soy sauce, etc). The foods tested in this analysis do not appear to be fermented or hydrolyzed. The use of a competitive ELISA on foods that are not fermented or hydrolyzed will most likely yield some interesting results. Despite information to the contrary in the body of the manuscript, the sandwich R5 ELISA was not used in the analysis. 


  • 16 samples (20.5%) of tested foods had gluten levels greater than or equal to 20 ppm.


Study 3:

Tricia Thompson and Suzanne Simpson. A comparison of gluten levels in labeled gluten-free and certified gluten-free foods sold in the United States. European Journal of Clinical Nutrition advance online publication,1 October 2014

Note: This study is based on data from Gluten Free Watchdog (

Number of labeled gluten-free foods tested: 158 products (46 certified); food purchased from retail establishments, including grocery stores and online merchants based on convenience (readily available in Massachusetts) or because a food was requested to be tested through Gluten Free Watchdog.

Categories of foods tested: baking ingredients, beverages, bread products, chili, condiments, cookies, crackers, entrees, flour, grains, gravy, hot cereal, mixes, nuts and seeds, pasta, ready-to-eat cereal, snack bars, snack food, soup, spices, supplements and tortillas.

Assay used: Ridascreen Gliadin R5 Sandwich ELISA (R7001) with cocktail extraction solution. If the food was suspected of containing gluten protein fragments owing to the use of certain fermented or hydrolyzed ingredients, it also was tested using the competitive R5 ELISA (Ridascreen Gliadin R7021) and extracted with ethanol.


  • Based on highest extraction test result, 8 samples (5.1 %) of tested foods, including 2 that were certified had gluten levels greater than or equal to 20 ppm gluten.

More information about this study is available at

My Thoughts

Why are the results of these studies so different? There are several possibilities:

We have very few studies assessing the gluten contamination levels of gluten-free food. Many more studies looking at a wide variety of foods in large numbers are needed before we can truly put together an accurate picture of levels of contamination in labeled gluten-free foods. In the meantime:

  • Please do not panic.
  • Look at the totality of the testing information we have to date.
  • If you are a subscriber to Gluten Free Watchdog continue to send along your testing requests.
  • Data is knowledge.
  • We need more data.

If you are interested in subscribing to Gluten Free Watchdog to see how the foods you are eating are testing please click here.

© October 10, 2014 by Tricia Thompson, MS, RD. All Rights Reserved. No part of this article may be reprinted without the express written permission of Tricia Thompson.

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