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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 for celiac 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 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 flour made from wheat).
A gluten-free diet rules out all ordinary breads, pastas, and many convenience foods; it also excludes gravies, custards, soups, and sauces thickened with wheat, rye, barley, or other gluten-containing flour. Various gluten-free bakery and pasta products are available from specialty retailers.
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.
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 ELISA method was designed to detect w-gliadins, but it suffered from the setback that it lacked sensitivity for barley prolamins.
In the processing of gluten-containing grains, gluten is removed as shown in the processing flow below:
Wheat Flour (80,000ppm) > Wheat Starch (200ppm) > Dextrin > Maltodextrin > Glucose Syrup (<5ppm) > Dextrose > Caramel Color
Since ordinary wheat flour contains approximately 12% gluten, even a tiny amount of wheat flour can cross-contaminate a gluten-free product, therefore, considerable care must be taken to prevent cross-contamination in both commercial and home food preparation.
Many so-called gluten-free products, such as chicken bouillon, corn cereal, and caramel ice cream topping, have been found to have been contaminated with gluten. For example, in an investigation reported by the Chicago Tribune on November 21, 2008, Wellshire Farms chicken nuggets labeled "gluten-free" were purchased from a Whole Foods Market and samples were sent to a food allergy laboratory at the University of Nebraska. Results of the testing indicated gluten was present in levels exceeding 2,000 ppm. After the article was published, the products continued to be sold. After receiving customer inquiries, however, more than a month later, the Whole Foods Market removed the product from their shelves. Wellshire Farms has since replaced the batter used in their chicken nuggets.
Chocolate has a slightly different issue. Pure chocolate is completely gluten free. Manufacturers, however, add various additives to improve taste. Even for chocolate that does not have additives that contain gluten, there is little possibility of contamination with gluten, from the use of machines which previously processed gluten containing food. Nevertheless, several vendors produce chocolate labeled "gluten free".
Lastly, some non-foodstuffs such as medications and vitamin supplements, especially those in tablet form, may contain gluten as an excipient or binding agent. People with gluten intolerances may therefore require specialist compounding of their medication.
A growing body of evidence suggests that a majority of people with celiac disease and following a gluten-free diet can safely consume pure oats in moderate amounts.
Special care is necessary when checking product ingredient lists since gluten comes in many forms: vegetable proteins and starch, modified food starch (when derived from wheat instead of maize), malt flavoring, unless specifically labeled as corn malt. Many ingredients contain wheat or barley derivatives. Maltodextrin is gluten-free, however, since it is highly modified, no matter what the source.
The suitability of oats in the gluten-free diet is still somewhat controversial. Some research suggests that oats in themselves are gluten-free, but that they are virtually always contaminated by other grains during distribution or processing. Recent research, however, indicated that a protein naturally found in oats (avenin) possessed peptide sequences closely resembling wheat gluten and caused mucosal inflammation in significant numbers of celiac disease sufferers. Some examination results show that even oats that are not contaminated with wheat particles are nonetheless dangerous, while not very harmful to the majority. Such oats are generally considered risky for children with celiac disease to eat, but two studies show that they are completely safe for adults with celiac disease to eat.
People who merely are "gluten-sensitive" may be able to eat oats without adverse effect, even over a period of five years. Given this conflicting information, excluding oats appears to be the only risk-free practice for celiac disease sufferers of all ages, however, medically approved guidelines exist for those with celiac disease who do wish to introduce oats into their diet.
Unless manufactured in a dedicated facility and under gluten-free practices, all cereal grains, including oats, may be cross-contaminated with gluten. Grains become contaminated with gluten by sharing the same farm, truck, mill, or bagging facility as wheat and other gluten-containing grains.
Several celiac disease groups report that according to the American Dietetic Association's "Manual of Clinical Dietetics", many types of alcoholic beverages are considered gluten-free, provided no colourings or other additives have been added as these ingredients may contain gluten. Although most forms of whiskey are distilled from a mash that includes grains that contain gluten, distillation removes any proteins present in the mash, including gluten. Although up to 49% of the mash for Bourbon and up to 20% of the mash for corn whiskey may be made up of wheat, or rye, all-corn Bourbons and corn whiskeys do exist, and are generally labeled as such. Spirits made without any grain such as brandy, wine, mead, cider, sherry, port, rum, tequila, and vermouth generally do not contain gluten. While some vineyards use a flour paste to caulk the oak barrels in which wine is aged, tests have shown that no detectable amounts of gluten are present in the wine from those barrels. A small number of vineyards have also used gluten as a clarifying agent, though it is not the standard process; some studies have shown small amounts of gluten to remain in the wine after clarification. Therefore, some people with Celiac or strong gluten sensitivity may wish to exercise caution. Liqueurs and pre-mixed drinks should be examined carefully for gluten-derived ingredients.
Almost all beers are brewed with malted barley or wheat and will contain gluten. Sorghum and buckwheat-based gluten-free beers are available, but remain a niche market. Some low-gluten beers are also available, however, there is disagreement over the use of gluten products in brewed beverages: Some brewers argue that in certain beers the proteins from such grains as barley or wheat are converted into amino acids during the clarification step of the brewing process and are therefore gluten-free, although there is evidence that this protein degradation is only partial. The Swedish government agency Livsmedelsverket carried out a study of the gluten content in a wide range of beers in 2005 and found that the majority of the beers tested contained less than 200 ppm gluten, with several brands containing less than 20 ppm. However, they also found that many beers have extremely high levels of gluten so, if unsure, coeliacs are advised to avoid beer.
Bread, which is a staple in many diets, typically is made from grains such as wheat that contain gluten. Wheat gluten contributes to the elasticity of dough and is thus an important component of bread. Gluten-free bread is made with ground flours from a variety of materials such as almonds, rice (rice bread), sorghum (sorghum bread), corn (cornbread), or legumes such as beans (bean bread), but since these flours lack gluten it can be difficult for them to retain their shape as they rise and they may be less "fluffy". Additives such as xanthum gum, guar gum, hydroxypropyl methylcellulose (HPMC), corn starch, or eggs are used to compensate for the lack of gluten.
In commerce, 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 recent 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.
Several organisations, such as the Gluten-Free Certification Organization (GFCO), the Celiac Sprue Association (CSA), and the National Foundation for Celiac Awareness (NFCA), also certify products and companies as gluten-free.
Many countries do not require labeling of gluten containing products, but in several countries (especially Australia and the European Union) new product labeling standards are enforcing the labeling of gluten-containing ingredients. In the United States, gluten may not be listed on the labels of certain foods because the U.S. Food and Drug Administration has classified gluten as GRAS (Generally Recognized As Safe). In the United Kingdom, only cereals currently need to be labeled regarding gluten, while other products are voluntary. For example, most British sausages contain Butcher's Rusk, a grain-derived food additive. Furthermore, while UK companies selling food prepared on their own premises are given guidance by the Food Standards Agency, they are not required to meet any labeling requirements.
Regulation of the label gluten-free varies. The current international Codex Alimentarius standard allows for 20 parts per million of gluten in so-called "gluten-free" foods for foodstuffs that are considered naturally gluten-free and 200 ppm for foodstuffs rendered gluten-free. Such a standard also reflects "the lowest level that can be consistently detected in foods." In the European Union, the European Commission issued regulations in 2009 limiting the use of "gluten-free" labels for food products to those with less than 20 mg/kg of gluten, and "very low gluten" labels for those with less than 100 mg/kg. In the United States, the FDA issued regulations in 2013 limiting the use of "gluten-free" labels for food products to those with less than 20 ppm of gluten. In the UK, foods may be labeled gluten-free if they contain less than 0.3% gluten. In Australia, gluten-free foods must contain less than 0.003% gluten. In Canada, Health Canada considers foods with a gluten-free claim which contain levels not exceeding 20 ppm as a result of cross-contamination to meet regulations.
Gluten-free fad diets have become popular. This may be because celiac disease was underdiagnosed and also that people are "unnecessarily turning to the diets as a food fad". There also appears to be an increased incidence of celiac disease, with one study which looked for antibodies from 1950s American blood samples finding that celiac disease is about four times as common as it was. Many are adopting gluten-free diets to treat celiac disease-like symptoms in the absence of a positive test for celiac disease.
A 2011 panel of celiac experts concluded that there is a condition related to gluten other than celiac disease and named it "non-celiac gluten sensitivity". However, for those without celiac disease or gluten sensitivity, the diet may be unnecessary. There are a wide variety of names which have been used in medical literature for gluten-related disorders which are different from celiac disease. Some of them are confusing and ambiguous. "Non-celiac gluten sensitivity" is the recommended umbrella term for conditions where symptoms different from celiac disease result from ingestion of gluten.
Despite some advocacy, evidence of the diet's efficacy as an autism treatment is poor. Despite vigorous marketing, a variety of studies, including a study by the University of Rochester, found that the popular autism diet does not demonstrate behavioral improvement and fails to show any genuine benefit to children diagnosed with autism who do not also have a known digestive condition which benefits from a gluten-free diet.
Many gluten-free products are not fortified or enriched by such nutrients as folate, iron, and fiber as traditional breads and cereals have been during the last century. Additionally, because gluten-free products are not always available, many Gluten-Sensitive Enteropathy (GSE) patients do not consume the recommended number of grain servings per day. People who change their standard gluten-free diet to implement gluten-free oats at breakfast, high fiber brown rice bread at lunch, and quinoa as a side at dinner have been found to have significant increases in protein (20.6 g versus 11 g), iron (18.4 mg versus 1.4 mg), calcium (182 mg versus 0 mg), and fiber (12.7 g versus 5 g). The B vitamin group did not have significant increases, but were still found to have improved values of thiamine, riboflavin, niacin, and folate. These dietary changes can greatly reduce a GSE patient's risk for anemia (especially Iron Deficiency Anemia) and low blood calcium levels or poor bone health.
Oats can increase intakes of vitamin B1, magnesium, and zinc in celiac disease patients in remission.
Selenium deficiency in gluten-free diet, combined with malabsorption of selenium in patients with uncontrolled celiac disease is considered a direct factor in the development of comorbid autoimmune thyroid diseases for celiac patients. 
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