The most frequently cited research that is used to determine gluten thresholds for people with celiac disease is a study by Catassi et al. They determined that more than 50 mg of gluten per day was harmful for people with celiac disease, but that some also showed villous atrophy at only 10 mg (1). Based on this research, the 10 mg threshold is usually used when talking about thresholds for gluten consumption for people with celiac disease.

Consuming a diet at 20 parts per million (ppm) is considered safe for those with celiac disease because it should put most people below the 10 mg threshold when you add up all the foods eaten in a day.

One important point to remember about parts per million (ppm) is that it is a concentration, not an amount, so it depends on how much of the food is consumed. For instance, you would have to eat 17 slices of gluten-free bread that contains 20 ppm gluten in order to hit the 10 mg threshold. But for regular wheat flour that contains thousands of ppm gluten, you only need the size of a pen tip to hit the limit.

The lower the ppm the better for foods like baked goods and pizza that people might consume large amounts of. For foods that people may only consume small amounts of, 20 ppm vs. 10 ppm or 5 ppm concentration is probably not going to make much of a difference, but some may be more sensitive than others.

Here is an infographic that explains it visually:

References:

1. Catassi C, Fabiani E, Iacono G, et al. A prospective, double-blind, placebo-controlled trial to establish a safe gluten threshold for patients with celiac disease. Am J Clin Nutr. 2007;85(1):160‐166. doi:10.1093/ajcn/85.1.160

https://www.ncbi.nlm.nih.gov/pubmed/17209192

Reviewed October 20, 2022.