A gluten-free diet is a diet that excludes foods containing gluten. Gluten is a protein found in wheat (including kamut and spelt), barley, rye, malts and triticale. It is used as a food additive in the form of a flavoring, stabilizing or thickening agent, often as "dextrin". A gluten-free diet is the only medically accepted treatment for celiac disease, the related condition dermatitis herpetiformis, and wheat allergy.
A gluten-free diet might also exclude oats. Medical practitioners are divided on whether oats are an allergen to celiac disease sufferers or if they are cross-contaminated in milling facilities by other allergens. Oats may also be contaminated when grown in rotation with wheat (wheat seeds from the previous harvest sprouting up again in the oat field and being harvested along with the oats).
The term gluten-free is generally used to indicate a supposed harmless level of gluten rather than a complete absence. The exact level at which gluten is harmless is uncertain and controversial. A 2008 systematic review tentatively concluded that consumption of less than 10 mg of gluten per day is unlikely to cause histological abnormalities, although it noted that few reliable studies had been done.
Regulation of the label gluten-free varies widely by country. In the United States, the FDA issued proposed regulations in 2007 limiting the use of "gluten-free" in food products to those with less than 20 parts per million of gluten. The current international Codex Alimentarius standard allows for 20 parts per million of gluten in so-called "gluten-free" foods. There is at least one website with a table containing information on "gluten-free" food manufacturers and the gluten parts per million levels to which each of those manufacturers tests.