If you have celiac disease, a new study warns you may need to be extra cautious of foods, which you assume to be naturally gluten-free.

Grains such as oats, millet, and rice don't contain the protein, which triggers an adverse response in those with celiac disease.

But, according to a survey published in the  Journal of the American Dietetic Association, some of the products they tested unexpectedly had traces of gluten.

Other products from the sample which weren't truly gluten-free, included millet flour, buckwheat flour, and sorghum flour.

It's most likely that this is the result of being grown, or processed, near grains that do contain gluten naturally.

Tricia Thompson, lead author on the study, said this:

There was some general assumption (among people with celiac disease) that those naturally gluten-free grains and flours weren't contaminated.  

The FDA limit for any product claiming to be gluten-free, is 20 parts contaminant per million parts product.

Researchers analyzed 22 naturally gluten-free grains, seeds, and flours. These were products which weren't specifically advertised as being gluten-free, and tested the amount of gluten contained in these products.

The Results:

  • 59% of the products contained less than the limit for gluten set out by the FDA.
  • 41% of the products contained more than the FDA limit.
  • 32% of the products wouldn't pass the FDA's gluten-free test.

Unfortunately, it's impossible to know how common it is for these products to be contaminated, as the sample size was too small.

So, what does this mean if you have celiac disease?

If you follow a gluten-free diet, but are still feeling unwell, it may be worthwhile taking a closer look at the foods you're eating, even those that you assume to be gluten-free.

These results suggest that you cannot rely on manufacturers to give voluntary allergen advice, on the products you purchase for gluten.

Instead, you should look for grains, seeds, and flours with the gluten-free label. Obviously, you can't always guarantee that these products are completely free from gluten, but it's much more likely that they will have been tested.

Ultimately, there needs to be a bigger push on the FDA to do more testing and regulation of gluten-free foods.