A gluten-free diet (GF diet) is a diet that excludes foods containing gluten. Gluten is a protein complex found in wheat (including kamut and spelt), barley, rye and triticale. A gluten-free diet is the only medically accepted treatment forceliac disease. Being gluten intolerant can often mean a person may also be wheat intolerant as well as suffer from the related inflammatory skin condition dermatitis herpetiformis, There are a smaller minority of people who suffer from wheat intolerance alone and are tolerant to gluten.

"Despite the health claims for gluten-free eating, there is no published experimental evidence to support such claims for the general population." A significant demand has developed for gluten-free food in the United States whether it is needed or not.

A gluten-free diet might also exclude oats. Medical practitioners are divided on whether oats are acceptable to celiac disease sufferers or whether they become cross-contaminated in milling facilities by other grains. Oats may also be contaminated when grown in rotation with wheat when wheat seeds from the previous harvest sprout up the next season in the oat field and are harvested along with the oats.

The exact level at which gluten is harmless for people with celiac disease is uncertain. A 2008 systematic review tentatively concluded that consumption of less than 10 mg of gluten per day for celiac disease patients is unlikely to cause histological abnormalities, although it noted that few reliable studies had been conducted.

Gluten-free food

Gluten-free food is normally seen as a diet for celiac disease, but people with a gluten allergy (an unrelated disease) should also avoid wheat and related grains.

Several grains and starch sources are considered acceptable for a gluten-free diet. The most frequently used are corn, potatoes, rice, and tapioca (derived from cassava). Other grains and starch sources generally considered suitable for gluten-free diets include amaranth, arrowroot, millet, montina, lupin, quinoa, sorghum (jowar), taro, teff, chia seed, almond meal flour, coconut flour, pea flour, cornstarch and yam. Sometimes various types of bean, soybean, and nut flours are used in gluten-free products to add protein and dietary fiber.

Almond flour has a low glycemic index. In spite of its name, buckwheat is not related to wheat. Pure buckwheat is considered acceptable for a gluten-free diet, however, many commercial buckwheat products are mixtures of wheat and buckwheat flours, and thus, not gluten-free. Gram flour, derived from chickpeas, also is gluten-free (this is not the same as Graham flourmade from wheat).

Gluten may be used in foods in some unexpected ways, for example it may be added as a stabilizing agent or thickener in products such as ice-cream and ketchup.

Cross-contamination issues

A gluten-free diet allows for fresh fruits, vegetables, meats, and many dairy products. The diet allows rice, corn, soy, potato, tapioca, beans, sorghum, quinoa, millet, pure buckwheat, arrowroot, amaranth, teff, Montina, and nut flours and the diet prohibits the ingestion of wheat, barley, rye, and related components, including triticale, durum, graham, kamut, semolina, spelt, malt, malt flavouring, or malt vinegar.

In the United States, the FDA considers foods containing less than or equal to 20 ppm to be gluten-free, but there is no regulation or law in the U.S. for labeling foods as 'gluten-free'. The finding of a current study indicates that some inherently gluten-free grains, seed, and flours not labeled gluten-free are contaminated with gluten. The consumption of these products can lead to inadvertent gluten intake. The use of highly sensitive assays is mandatory to certify gluten-free food products. The European Union, World Health Organization, and Codex Alimentarius require reliable measurement of the wheat prolamins, gliadins rather than all-wheat proteins.

There still is no general agreement on the analytical method used to measure gluten in ingredients and food products. The official limits described in the Codex Draft are 20 ppm for foodstuffs that are considered naturally gluten-free and 200 ppm for foodstuffs rendered gluten-free. The ELISA method was designed to detect w-gliadins, but it suffered from the setback that it lacked sensitivity for barley prolamins.