The type of gluten that causes reactions in those with celiac disease and gluten sensitivity occurs in the grains i.e., the seeds produced by the grass plants wheat, barley and rye. (For more explanation of this, see my article What Is Gluten.)
Pure wheat grass and barley grass (just the grass, with absolutely no seeds) do not contain gluten.
In fact, the U.S. Food and Drug Administration, in its finalized gluten-free label rules, has said that wheat grass and barley grass could be used to make foods labeled gluten-free, as long as the finished products contain less than 20 parts per million of gluten.
Details Matter In Production of Gluten-Free Wheat, Barley Grass Products
However, while wheat grass and barley grass in their pure forms are considered gluten-free, it matters how they're harvested and how products containing them are produced.
For example, if a farmer allows some of the grasses to begin producing seeds prior to harvest, then that particular crop will contain gluten.
In addition, if a manufacturer of supplements produces gluten-containing products alongside or on the same equipment as it's using for gluten-free labeled products, then those products can be cross-contaminated unless special precautions are taken, and they may contain gluten.
So when it comes to the question of whether wheat grass and barley grass can be considered gluten-free, the details really matter.
Dietitian Tricia Thompson, a specialist in celiac disease and gluten-free diet issues, recommends avoiding any product containing wheat or barley grass that's not specifically labeled gluten-free.
In addition, she also recommends avoiding any gluten-free-labeled product containing wheat or barley grass unless you can verify that it's been tested for gluten cross-contamination with a specific type of test: the R5 ELISA test. Other forms of testing may not produce accurate results, since they may underestimate the amount of barley gluten in the product.
Other Vegetables Provide Same Benefits as Grasses
Despite the sometimes-wild claims for the health benefits of wheat and barley grass, other green vegetables will provide you with roughly the same nutrients or even more of certain vital vitamins and minerals.
For example, there's more iron, potassium, calcium and magnesium in leafy green spinach than there is in wheat grass juice, according to the U.S. Department of Agriculture. Wheat grass juice turns out to be a slightly superior source of vitamin E, but spinach and broccoli provide significantly more vitamin C.
The bottom line is, there's really nothing in wheat grass or barley grass that you can't get from other green plants. It may be possible to find a properly tested gluten-free supplement containing one or both of those grasses, but you'd be better off sticking with supplements that don't include potentially risky ingredients and using whole green plants, such as spinach, kale and chard, to fulfill your nutritional needs.