Properly handle gluten free oats

[szmi]

Oats are tolerated by the majority of people with coeliac disease, and food containing oats can be labelled as gluten free.

Quote from https://celiac.org/gluten-free-living/gluten-free-foods/label-reading-the-fda/

4. May oats be labeled gluten-free?
   Oats that contain less than 20 ppm of gluten may be labeled gluten-free. Oats do not need to be certified gluten-free. Some people with celiac disease may have an immune reaction to the avenin in oats, a protein similar to gluten, even if labeled gluten-free. It is important to speak with your gastroenterologist or dietitian about whether you should include oats in your gluten-free diet.

Therefore it is confusing and wrong that OFF automatically adds "Gluten" as an allergen if oat is an ingredient. This happens even if the "No gluten" label has been added.

However, this is a special case, and in most cases (if not explicitly labelled gluten free) oats are indeed likely cross contaminated with wheat.

So I think the "No gluten" label should override detection of gluten from ingredients.

Also possibly oats should be added as a separate allergen, since there is a minority of people with coeliac disease that are also sensitive to avenin, which is the similar to wheat gluten.

E.g. see this product:

https://world.openfoodfacts.org/product/4305615826592

[aleene]

Oats is officially not gluten free as it is often contaminated by other cereals during the production processes. So if you are intolerant, only use oats that has a verified gluten free label. If you are just sensitive you can have a go at oats.
But you are right if there is a verified label, it should be marked as gluten free. Otherwise it should be gluten maybe.

[aleene]

At the moment the taxonomy allergens.txt contains an entry en:oats and en:oat fiber and possible translations. Best is to take these entries out.
This can be part of a project that moves the allergens into the ingredients and marks them up in the same way as vegetarian. Now we have to maintain two dependent taxonomies.

[szmi]

Thanks @aleene. So I think short term fix is that when "No gluten" label is set, "Gluten" is automatically removed from the allergen and trace allergen lists.

In fact some gluten-free labelled foods have emphasized wheat starch in the ingredients list (any wheat content must be emphasized as an allergen), yet when producing the starch the gluten content is reduced to below the 20mg/kg limit. So making the label take priority would allow properly handling this case as well.

Longer term, I think it would be nice if matching preferences would allow excluding individual ingredients (like oat). So a person with coeliac disease with sensitivity to oats would select "Without gluten" and add "oats" to the excluded ingredients. This would also allow full flexibility for individuals with special food allergies that are not listed in the common allergen list. I'll open a separate feature request for this.

[github-actions]

This issue has been open 90 days with no activity. Can you give it a little love by linking it to a parent issue, adding relevant labels and projets, creating a mockup if applicable, adding code pointers from https://github.com/openfoodfacts/openfoodfacts-server/blob/main/.github/labeler.yml, giving it a priority, editing the original issue to have a more comprehensive description… Thank you very much for your contribution to 🍊 Open Food Facts