Nutrixe“Gluten-free” does not mean zero gluten. It means less than 20 milligrams per kilo: 20 parts per million, 20 ppm. The figure is everywhere: in regulations, on logos, on analysis certificates. But where does it come from? Why 20, and not 10, 50 or 0? The answer comes down to two constraints: what the gut tolerates, and what the laboratory can measure.
What a celiac gut tolerates
Celiac disease is an autoimmune reaction triggered by gluten, which damages the lining of the small intestine. The question researchers asked in the 2000s was pragmatic: how much gluten a day can a person with celiac disease absorb without damage?
The most cited study is an Italian trial published in 2007 (Catassi et al.): for three months, adults with celiac disease in remission received daily capsules containing 0, 10 or 50 mg of gluten, without knowing which. At 50 mg a day, the intestinal mucosa showed damage. At 10 mg a day, most participants showed none, with individual variation, one person having reacted even at the low dose.
That range served as the basis. An ordinary diet contains around 300 g a day of cereal or processed products. At 20 ppm, that is about 6 mg of gluten a day: below the 10 mg judged without effect for the majority, with a margin. At 100 ppm it would be 30 mg, too close to the zone where damage appears.
What the laboratory can measure
The other constraint is technical. Gluten is measured by immunological tests (ELISA, the so-called R5 method), which recognise fragments of the protein. These tests have a detection limit of a few ppm and a reliable quantification limit a little higher. Requiring “zero” would amount to requiring “below what we can measure”, which varies by method, laboratory and food type (hydrolysed gluten in fermented products is harder to measure).
A 20 ppm threshold is therefore also a verifiable threshold: far enough above detection limits for a result to be reproducible from one laboratory to another.
International convergence, with exceptions
The Codex Alimentarius, the international reference, set 20 ppm in 2008. The European Union adopted it in Implementing Regulation 828/2014, applicable from 2016, adding a “very low gluten” claim for products between 20 and 100 ppm, unsuitable for people with celiac disease and rare on shelves. The United States adopted the same threshold in the FDA rule of 2013. So did Canada.
But not everyone followed:
- Australia and New Zealand require no detectable gluten for the “gluten free” claim. That is why wheat starch is banned there in those products, while it is allowed in Europe; we devote an article to it.
- The private American certification GFCO requires under 10 ppm.
- Argentina uses 10 ppm for its national logo.
It is not that the science differs from one country to another; it is that the cursor between protection and industrial feasibility was placed differently.
What the threshold does not say
Three limits to keep in mind.
It is calibrated for the majority. A minority of people with celiac disease react below 20 ppm. They usually only find out after noticing that compliant products make them ill.
It does not stack. The reasoning assumes an ordinary diet. Someone who eats a lot of processed “gluten-free” products all close to the threshold may exceed the daily 10 mg. Rare, but possible.
It only applies to packaged products. In a restaurant nobody measures. A shared fryer or a shared board can bring far more than 20 ppm; that is the whole point of our article on cross-contamination, and the reason Nutrixe distinguishes dedicated kitchens from menus “with options”.
In short
- 20 ppm = 20 mg/kg, the “gluten-free” threshold in Europe, the United States, Canada and the Codex.
- It comes from clinical trials (10 mg/day without damage, 50 mg/day with) and from laboratory measurement limits.
- Australia requires “not detectable”; some private certifications 10 ppm.
- It protects the majority in an ordinary diet, not everyone in every circumstance.
- It says nothing about what happens in a restaurant kitchen.
This information is no substitute for medical advice. If you react to compliant products, talk to your gastroenterologist: it exists, it can be documented, and it changes the dietary strategy.
