A gluten-free diet (GFD) is a diet that strictly excludes gluten, a mixture of proteins found in wheat and related grains, including barley, rye, oat, and all their species and hybrids (such as spelt, kamut, and triticale). The inclusion of oats in a gluten-free diet remains controversial, and may depend on the oat cultivar and the frequent cross-contamination with other gluten-containing cereals.
Gluten causes health problems for those with gluten-related disorders, including celiac disease (CD), non-celiac gluten sensitivity (NCGS), gluten ataxia, dermatitis herpetiformis (DH), and wheat allergy. In these people, the gluten-free diet is demonstrated as an effective treatment, but several studies show that about 79% of the people with coeliac disease have an incomplete recovery of the small bowel, despite a strict gluten-free diet. This is mainly caused by inadvertent ingestion of gluten. People with poor basic education and understanding of gluten-free diet often believe that they are strictly following the diet, but are making regular errors.
In addition, a gluten-free diet may, in at least some cases, improve gastrointestinal or systemic symptoms in diseases like irritable bowel syndrome, rheumatoid arthritis, multiple sclerosis or HIV enteropathy, among others. Gluten-free diets have also been promoted as an alternative treatment of people with autism, but the current evidence for their efficacy in making any change in the symptoms of autism is limited and weak.
Gluten proteins have low nutritional and biological value, and the grains that contain gluten are not essential in the human diet. However, an unbalanced selection of food and an incorrect choice of gluten-free replacement products may lead to nutritional deficiencies. Replacing flour from wheat or other gluten-containing cereals with gluten-free flours in commercial products may lead to a lower intake of important nutrients, such as iron and B vitamins. Some gluten-free commercial replacement products are not enriched or fortified as their gluten-containing counterparts, and often have greater lipid / carbohydrate content. Children especially often over-consume these products, such as snacks and biscuits. Nutritional complications can be prevented by a correct dietary education.
A gluten-free diet should be mainly based on naturally gluten-free foods with a good balance of micro and macro nutrients: meat, fish, eggs, milk and dairy products, legumes, nuts, fruits, vegetables, potatoes, rice, and maize are all appropriate components of such a diet. If commercially prepared, gluten-free replacement products are used, choosing those that are enriched or fortified with vitamins and minerals is preferable. Pseudocereals (quinoa, amaranth, and buckwheat) and some minor cereals are healthy alternatives to these prepared products and have high biological and nutritional value.
Rationale behind adoption of the diet
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Coeliac disease
Coeliac disease (American English: celiac) (CD) is a chronic, immune-mediated, and mainly intestinal process, caused by the ingestion of wheat, barley, rye and derivatives, that appears in genetically predisposed people of all ages. CD is not only a gastrointestinal disease, because it may affect several organs and cause an extensive variety of non-gastrointestinal symptoms, and most importantly, it may often be completely asymptomatic. Added difficulties for diagnosis are the fact that serological markers (anti-tissue transglutaminase [TG2]) are not always present and many people with coeliac may have minor mucosal lesions, without atrophy of the intestinal villi.
CD affects approximately 1-2% of the general population all over the world and is on the increase, but most cases remain unrecognized, undiagnosed and untreated, exposing patients to the risk of long-term complications. People may suffer severe disease symptoms and be subjected to extensive investigations for many years before a proper diagnosis is achieved. Untreated CD may cause malabsorption, reduced quality of life, iron deficiency, osteoporosis, obstetric complications (stillbirth, intrauterine growth restriction, preterm birth, low birthweight, and small for gestational age), an increased risk of intestinal lymphomas and greater mortality. CD is associated with some autoimmune diseases, such as diabetes mellitus type 1, thyroiditis, gluten ataxia, psoriasis, vitiligo, autoimmune hepatitis, dermatitis herpetiformis, primary sclerosing cholangitis, and more.
CD with “classic symptomsâ€, which include gastrointestinal manifestations such as chronic diarrhoea and abdominal distention, malabsorption, loss of appetite, and impaired growth, is currently the least common presentation form of the disease and affects predominantly to small children generally younger than two years of age.
CD with “non-classic symptoms†is the most common clinical type and occurs in older children (over 2 years old), adolescents and adults. It is characterized by milder or even absent gastrointestinal symptoms and a wide spectrum of non-intestinal manifestations that can involve any organ of the body, and very frequently may be completely asymptomatic both in children (at least in 43% of the cases) and adults.
Following a lifelong gluten-free diet is the only medically-accepted treatment for people with coeliac disease.
Non-coeliac gluten sensitivity
Non-coeliac gluten sensitivity (NCGS) is described as a condition of multiple symptoms that improves when switching to a gluten-free diet, after coeliac disease and wheat allergy are excluded. People with NCGS may develop gastrointestinal symptoms, which resemble those of irritable bowel syndrome (IBS) or a variety of nongastrointestinal symptoms.
Gastrointestinal symptoms may include any of the following: abdominal pain, bloating, bowel habit abnormalities (either diarrhea or constipation), nausea, aerophagia, gastroesophageal reflux disease, and aphthous stomatitis. A range of extra-intestinal symptoms, said to be the only manifestation of NCGS in the absence of gastrointestinal symptoms, have been suggested, but remain controversial. These include: headache, migraine, "foggy mind", fatigue, fibromyalgia, joint and muscle pain, leg or arm numbness, tingling of the extremities, dermatitis (eczema or skin rash), atopic disorders such as asthma, rhinitis, other allergies, depression, anxiety, iron-deficiency anemia, folate deficiency or autoimmune diseases. NCGS has also been controversially implicated in some neuropsychiatric disorders, including schizophrenia, eating disorders, autism, peripheral neuropathy, ataxia and attention deficit hyperactivity disorder (ADHD). Above 20% of people with NCGS have IgE-mediated allergy to one or more inhalants, foods or metals, among which most common are mites, graminaceae, parietaria, cat or dog hair, shellfish and nickel. Approximately, 35% of people with NCGS suffer other food intolerances, mainly lactose intolerance.
The pathogenesis of NCGS is not yet well understood. It was hypothesized that gluten, as with coeliac disease, is the cause of NCGS. Much recent research on NCGS has aimed at determining which agents trigger a response in people with NCGS: to which extent gluten, FODMAPs, ATIs (plant-derived proteins present in glutencontaining cereals and gluten) or wheat germ agglutinin are involved. For these reasons, NCGS is a controversial syndrome and some authors still question it. In a 2013 double-blind placebo-controlled trial (DBPC) by Biesiekierski et al. in a few people with irritable bowel syndrome (IBS), the authors found no difference between gluten or placebo groups and the concept of NCGS as a syndrome was questioned. Nevertheless, this study seems to have design errors and an incorrect selection of participants, which could have masked the true effect of gluten reintroduction. In a review of May 2015 published in Gastroenterology, Fasano et al. conclude that besides gluten, ATIs and FODMAPs present in gluten, wheat, barley, rye, and their derivatives play a role in the development of NCGS symptoms. ATIs, which resist proteolytic digestion, may be the inducers of innate immunity in people with coeliac disease or NCGS. FODMAPs cause mild wheat intolerance at most, which is mainly limited to gastrointestinal symptoms.
After exclusion of coeliac disease and wheat allergy, the subsequent step for diagnosis and treatment of NCGS is to start a strict gluten-free diet to assess if symptoms improve or resolve completely. This may occur within days to weeks of starting a GFD, but improvement may also be due to a non-specific, placebo response. Recommendations may resemble those for coeliac disease, for the diet to be strict and maintained, with no transgression. The degree of gluten cross contamination tolerated by people with NCGS is not clear but there is some evidence that they can present with symptoms even after consumption of small amounts. It is not yet known whether NCGS is a permanent or a transient condition. A trial of gluten reintroduction to observe any reaction after 1â€"2 years of strict gluten-free diet might be performed.
A subgroup of people with NCGS may not improve by eating commercially available gluten-free products, which are usually rich of preservatives and additives, because chemical additives (such as sulphites, glutamates, nitrates and benzoates) might have a role in evoking functional gastrointestinal symptoms of NCGS. These people may benefit from a diet with a low content of preservatives and additives.
NCGS, which is possibly immune-mediated, now appears to be more common than coeliac disease, with prevalence rates between 0.5â€"13% in the general population.
Wheat allergy
People can also experience adverse effects of wheat as result of a wheat allergy. Gastrointestinal symptoms of wheat allergy are similar to those of coeliac disease and non-coeliac gluten sensitivity, but there is a different interval between exposure to wheat and onset of symptoms. Wheat allergy has a fast onset (from minutes to hours) after the consumption of food containing wheat and could be anaphylaxis.
The management of wheat allergy consists of complete withdrawal of any food containing wheat and other gluten-containing cereals. Nevertheless, some people with wheat allergy can tolerate barley, rye or oats.
Gluten ataxia
Gluten ataxia is an autoimmune disease triggered by the ingestion of gluten. With gluten ataxia, damage takes place in the cerebellum, the balance center of the brain that controls coordination and complex movements like walking, speaking and swallowing, with loss of Purkinje cells. People with gluten ataxia usually present gait abnormality or incoordination and tremor of the upper limbs. Gaze-evoked nystagmus and other ocular signs of cerebellar dysfunction are common. Myoclonus, palatal tremor, and opsoclonus-myoclonus may also appear.
Early diagnosis and treatment with a gluten-free diet can improve ataxia and prevent its progression. The effectiveness of the treatment depends on the elapsed time from the onset of the ataxia until diagnosis, because the death of neurons in the cerebellum as a result of gluten exposure is irreversible.
Gluten ataxia accounts for 40% of ataxias of unknown origin and 15% of all ataxias. Less than 10% of people with gluten ataxia present any gastrointestinal symptom, yet about 40% have intestinal damage.
As a fad diet
Since the beginning of the 21st century, the gluten-free diet has become the most popular trendy fad diet in the United States and other countries. Clinicians worldwide have been challenged by an increasing number of people who do not have coeliac disease nor wheat allergy, with digestive or extra-digestive symptoms which improved removing wheat / gluten from the diet. Many of these persons began a gluten-free diet on their own, without having been previously evaluated. Another reason that contributed to this trend was the publication of several books that demonize gluten and point to it as a cause of type 2 diabetes, weight gain and obesity, and a broad list of diseases ranging from depression and anxiety to arthritis and autism. The book that has had the most impact is Grain Brain: The Surprising Truth about Wheat, Carbs, and Sugar - Your Brain's Silent Killers, by the American neurologist David Perlmutter, published on September 2013. Another book that has had great impact is Wheat Belly: Lose the Wheat, Lose the Weight, and Find Your Path Back to Health, by the cardiologist William Davis, which refers to wheat as a "chronic poison" and became a New York Times bestseller within a month of publication in 2011. The gluten-free diet has been advocated and followed by many celebrities to lose weight, such as Miley Cyrus, Gwyneth Paltrow, and Kourtney Kardashian, and are used by some professional athletes, who believe the diet can improve energy and health. It became popular in USA, as the popularity of low-carbohydrate diets faded.
Estimates suggest that in 2014, 30% of people in USA and Australia were consuming gluten-free foods, with a growing number, calculated from surveys that by 2016 approximately 100 million Americans would consume gluten-free products. Data from a 2015 Nielsen survey of 30,000 adults in 60 countries around the world conclude that 21% of people prefer to buy gluten-free foods, being the highest interest among the younger generations. In USA, it was estimated that more than half of people who buy foods labeled gluten-free do not have a clear reaction to gluten, and they do so "because they think it will help them lose weight, because they seem to feel better or because they mistakenly believe they are sensitive to gluten." Although gluten is highly immunologically reactive and humans appear not to have evolved to digest it well, a gluten-free diet is not a healthier option for the general population, other than people suffering from gluten-related disorders or other associated conditions which improve with a gluten-free diet in some cases, such as irritable bowel syndrome and certain autoimmune and neurological disorders. There is no published experimental evidence to support that the gluten-free diet contributes to weight loss.
In a review of May 2015 published in Gastroenterology, Fasano et al. conclude that, although there is an evident "fad component" to the recent rise in popularity of the gluten-free diet, there is also growing and unquestionable evidence of the existence of non-coeliac gluten sensitivity.
The popularity of the gluten-free diet is hurting people who actually need to eliminate gluten due to medical reasons. The servers are issuing judgments, believing that it is simply a fad, which is leading to them not taking the necessary precautions in the handling of the food to avoid gluten cross-contamination. "In other words, the customers who 'order gluten-free meals washed down with a gluten-filled beer' are essentially making a mockery of a serious issue". Even many professionals in the medical field think that the gluten-free diet is just a fad. On the other hand, the popularity of the gluten-free diet has increased the availability of commercial gluten-free replacement products and gluten-free grains.
Gluten-free commercial replacement products, such as gluten-free cakes, are more expensive than their gluten-containing counterparts, so their purchase adds a financial burden. They are also typically higher in calories, fat, and sugar, and lower in dietary fiber. In less developed countries, wheat can represent an important source of protein, since it is a substantial part of the diet in the form of bread, noodles, bulgur, couscous, and other products.
Healthcare professionals recommend against undertaking a gluten-free diet as a form of self-diagnosis, because tests for coeliac disease are reliable only if the person has been consuming gluten recently. There is a consensus in the medical community that people should consult a physician before going on a gluten-free diet, so that a medical professional can accurately test for coeliac disease or any other gluten-induced health issues.
Although popularly used as an alternative treatment for people with autism, there is no good evidence that a gluten-free diet is of benefit in reducing the symptoms of autism.
Eating gluten-free
A gluten-free diet is a diet that strictly excludes gluten, proteins present in wheat (and all wheat varieties such as spelt and kamut), barley, rye, oat, and derivatives of these grains such as malt and triticale, and foods that may include them, or shared transportation or processing facilities with them. The inclusion of oats in a gluten-free diet remains controversial. Oat toxicity in people with gluten-related disorders depends on the oat cultivar consumed because the immunoreactivities of toxic prolamins are different among oat varieties. Furthermore, oats are frequently cross-contaminated with the other gluten-containing cereals. Pure oat (labelled as "pure oat" or "gluten-free oat") refers to oats uncontaminated with any of the other gluten-containing cereals. Some cultivars of pure oat could be a safe part of a gluten-free diet, requiring knowledge of the oat variety used in food products for a gluten-free diet. Nevertheless, the long-term effects of pure oats consumption are still unclear and further studies identifying the cultivars used are needed before making final recommendations on their inclusion in the gluten-free diet.
Other grains, although gluten-free in themselves, may contain gluten by cross-contamination with gluten-containing cereals during grain harvesting, transporting, milling, storing, processing, handling or cooking.
Processed foods commonly contain gluten as an additive (as emulsifiers, thickeners, gelling agents, fillers, and coatings), so they would need specific labeling. Unexpected sources of gluten are, among others, processed meat, vegetarian meat substitutes, reconstituted seafood, stuffings, butter, seasonings, marinades, dressings, confectionary, candies, and ice cream.
Cross contamination in the home is also a consideration for those who suffer gluten-related disorders. There can be many sources of cross contamination, as for example when family members prepare gluten-free and gluten-containing foods on the same surfaces (counter tops, tables, etc.) or share utensils that have not been cleaned after being used to prepare gluten-containing foods (cutting boards, colanders, cutlery, etc.), kitchen equipment (toaster, cupboards, etc.) or certain packaged foods (butter, peanut butter, etc.).
Medications and dietary supplements are made using excipients that may contain gluten.
The gluten-free diet includes naturally gluten-free food, such as meat, fish, seafood, eggs, milk and dairy products, nuts, legumes, fruit, vegetables, potatoes, pseudocereals (in particular amaranth, buckwheat, chia seed, quinoa), only certain cereal grains (corn, rice, sorghum), minor cereals (including fonio, Job's tears, millet, teff, called "minor" cereals as they are "less common and are only grown in a few small regions of the world"), some other plant products (arrowroot, mesquite flour, sago, tapioca) and products made from these gluten-free foods.
Risks
An unbalanced selection of food and an incorrect choice of gluten-free replacement products may lead to nutritional deficiencies. Replacing flour from wheat or other gluten-containing cereals with gluten-free flours in commercial products may lead to a lower intake of important nutrients, such as iron and B vitamins and a higher intake of sugars and saturated fats. Some gluten-free commercial replacement products are not enriched or fortified as their gluten-containing counterparts, and often have greater lipid / carbohydrate content. Children especially often over-consume these products, such as snacks and biscuits. These nutritional complications can be prevented by a correct dietary education. Pseudocereals (quinoa, amaranth, and buckwheat) and some minor cereals are healthy alternatives to these prepared products and have higher biological and nutritional value. Advances towards higher nutrition-content gluten-free bakery products, improved for example in terms of fiber content and glycemic index, have been made by using not exclusively corn starch or other starches to substitute for flour. In this aim, for example the dietary fiber inulin (which acts as a prebiotic) or quinoa or amaranth wholemeal have been as substitute for part of the flour. Such substitution has been found to also yield improved crust and texture of bread. It is recommended that anyone embarking on a gluten-free diet check with a registered dietitian to make sure they are getting the required amount of key nutrients like iron, calcium, fiber, thiamin, riboflavin, niacin and folate. Vitamins often contain gluten as a binding agent. Experts have advised that it is important to always read the content label of any product that is intended to be swallowed.
Up to 30% of people with known coeliac disease often continue having or redeveloping symptoms. Also, a lack of symptoms or negative blood antibodies levels are not reliable indicators of intestinal recuperation. Several studies show an incomplete recovery of small bowel despite a strict gluten-free diet, and about 79% of such people have persistent villous atrophy. This lack of recovery is mainly caused by inadvertent exposure to gluten. People with poor basic education and understanding of the gluten-free diet often believe that they are strictly following the diet, but are making regular errors. In addition, some people often deliberately continue eating gluten because of limited availability, inferior taste, higher price, and inadequate labelling of gluten-free products. Poor compliance with the regimen is also influenced by age at diagnosis (adolescents), ignorance of the consequences of the lack of a strict treatment and certain psychological factors. Ongoing gluten intake can cause severe disease complications, such as various types of cancers (both intestinal and extra-intestinal) and osteoporosis.
Regulation and labels
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 10Â mg (10Â ppm) 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 by country. Most countries derive key provisions of their gluten-free labeling regulations from the Codex Alimentarius international standards for food labeling as a standard relating to the labeling of products as gluten-free. It only applies to foods that would normally contain gluten. Gluten-free is defined as 20 ppm (= 20Â mg/kg) or less. It categorizes gluten-free food as:
- Food that is gluten-free by composition
- Food that has become gluten-free through special processing.
- Reduced gluten content, food which includes food products with between 20 and 100 ppm of gluten Reduced gluten content is left up to individual nations to more specifically define.
The Codex Standard suggests the enzyme-linked Immunoassay (ELISA) R5 Mendez method for indicating the presence of gluten, but allows for other relevant methods, such as DNA. The Codex Standard specifies that the gluten-free claim must appear in the immediate proximity of the name of the product, to ensure visibility.
There 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. 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.
Australia
The Australian government recommends that:
- food labeled gluten-free include no detectable gluten (<3ppm ) oats or their products, cereals containing gluten that have been malted or their products
- food labeled low gluten claims such that the level of 20Â mg gluten per 100 g of the food
Brazil
All food products must be clearly labelled whether they contain gluten or they are gluten-free. Since April 2016, the declaration of the possibility of cross-contamination is mandatory when the product does not intentionally add any allergenic food or its derivatives, but the Good Manufacturing Practices and allergen control measures adopted are not sufficient to prevent the presence of accidental trace amounts. When a product contains the warning of cross-contamination with wheat, rye, barley, oats and their hybridised strains, the warning "contains gluten" is mandatory. The law does not establish a gluten threshold for the declaration of its absence.
Canada
Health Canada considers that foods containing levels of gluten not exceeding 20 ppm as a result of contamination, meet the health and safety intent of section B.24.018 of the Food and Drug Regulations when a gluten-free claim is made. Any intentionally added gluten, even at low levels must be declared on the packaging and a gluten-free claim would be considered false and misleading. Labels for all food products sold in Canada must clearly identify the presence of gluten if it is present at a level greater than 10 ppm.
European Union
The EU European Commission delineates the categories as:
- gluten-free: 20 ppm or less of gluten
- very low gluten foodstuffs: 20-100ppm gluten.
All foods containing gluten as an ingredient must be labelled accordingly as gluten is defined as one of the 14 recognised EU allergens.
United States
Until 2012 anyone could use the gluten-free claim with no repercussion. In 2008, Wellshire Farms chicken nuggets labeled gluten-free were purchased and samples were sent to a food allergy laboratory where they were found to contain gluten. After this was reported in the Chicago Tribune, the products continued to be sold. The manufacturer has since replaced the batter used in its chicken nuggets. The U.S. first addressed gluten-free labeling in the 2004 Food Allergen Labeling and Consumer Protection Act (FALCPA). The Alcohol and Tobacco Tax and Trade Bureau published interim rules and proposed mandatory labeling for alcoholic products in 2006. The FDA issued their Final Rule on August 5, 2013. When a food producer voluntarily chooses to use a gluten-free claim for a product, the food bearing the claim in its labeling may not contain:
- an ingredient that is a gluten-containing grain
- an ingredient that is derived from a gluten-containing grain that has not been processed to remove gluten
- an ingredient that is derived from a gluten-containing grain, that has been processed to remove gluten but results in the presence of 20 ppm or more gluten in the food. Any food product claiming to be gluten-free and also bearing the term "wheat" in its ingredient list or in a separate "Contains wheat" statement, must also include the language "*the wheat has been processed to allow this food to meet the FDA requirements for gluten-free foods," in close proximity to the ingredient statement.
Any food product that inherently does not contain gluten may use a gluten-free label where any unavoidable presence of gluten in the food bearing the claim in its labeling is below 20 ppm gluten.
See also
- Gluten-free, casein-free diet
- Specific Carbohydrate Diet
- Paleolithic diet
- 2010s in food
References
