The quick answer is that it can be either, but it all depends on the individual.
What is Gluten?
Gluten is a protein naturally found in some grains including wheat, barley, and rye. It acts like a binder, holding food together and adding a “stretchy” quality—think of a pizza maker tossing and stretching out a ball of dough. Without gluten, the dough would rip easily.
Other grains that contain gluten are wheat berries, spelt, durum, emmer, semolina, farina, farro, graham, khorasan wheat, einkorn, and triticale (a blend of wheat and rye). Oats—though naturally gluten free—often contain gluten from cross-contamination when they are grown near, or processed in the same facilities as the grains listed above. Gluten is also sold as wheat gluten, or seitan, a popular vegan high-protein food. Less obvious sources of gluten include soy sauce and modified food starch, however gluten-free options of these products are available and labeled as such to comply with the U.S. Food and Drug Administration’s gluten-free labeling rule.
Gluten and Health Benefits
Gluten is most often associated with wheat and wheat-containing foods that are abundant in our food supply. Negative media attention on wheat and gluten has caused some people to doubt its place in a healthful diet. There is little published research to support these claims; in fact published research suggests the opposite.
In a 2017 study of over 100,000 participants without celiac disease, researchers found no association between long-term dietary gluten consumption and heart disease risk.  In fact, the findings also suggested that non-celiac individuals who avoid gluten may increase their risk of heart disease, due to the potential for reduced consumption of whole grains.
- Many studies have linked whole grain consumption with improved health outcomes. For example, groups with the highest intakes of whole grains including wheat (2-3 servings daily) compared with groups eating the lowest amounts (less than 2 servings daily) were found to have significantly lower rates of heart disease and stroke, development of type 2 diabetes, and deaths from all causes. [2-5]
Gluten may also act as a prebiotic, feeding the “good” bacteria in our bodies. Arabinoxylan oligosaccharide is a prebiotic carbohydrate derived from wheat bran that has been shown to stimulate the activity of bifidobacteria in the colon. These bacteria are normally found in a healthy human gut. Changes in their amount or activity have been associated with gastrointestinal diseases including inflammatory bowel disease, colorectal cancer, and irritable bowel syndrome. [6,7]
When Gluten Is a Problem
What’s not great about gluten is that it can cause serious side effects in certain individuals. Some people react differently to gluten, where the body senses it as a toxin, causing one’s immune cells to overreact and attack it. If an unknowingly sensitive person continues to eat gluten, this creates a kind of battle ground resulting in inflammation. The side effects can range from mild (fatigue, bloating, alternating constipation and diarrhea) to severe (unintentional weight loss, malnutrition, intestinal damage) as seen in the autoimmune disorder celiac disease. Estimates suggest that 1 in 133 Americans has celiac disease, or about 1% of the population, but about 83% of them are undiagnosed or misdiagnosed with other conditions. [8,9] Research shows that people with celiac disease also have a slightly higher risk of osteoporosis and anemia (due to malabsorption of calcium and iron, respectively); infertility; nerve disorders; and in rare cases cancer.  The good news is that removing gluten from the diet may reverse the damage. A gluten-free diet is the primary medical treatment for celiac disease. However, understanding and following a strict gluten-free diet can be challenging, possibly requiring the guidance of a registered dietitian to learn which foods contain gluten and to ensure that adequate nutrients are obtained from gluten-free alternatives. Other conditions that may require the reduction or elimination of gluten in the diet include:
- Non-celiac gluten sensitivity, also referred to as gluten sensitive enteropathy (GSE) or gluten intolerance—An intolerance to gluten with similar symptoms as seen with celiac disease, but without the accompanying elevated levels of antibodies and intestinal damage. There is not a diagnostic test for GSE but is determined by persistent symptoms and a negative diagnostic celiac test.
- Wheat allergy—An allergy to one or more of the proteins (albumin, gluten, gliadin, globulin) found in wheat, diagnosed with positive immunoglobulin E blood tests and a food challenge. Compare this with celiac disease, which is a single intolerance to gluten. Symptoms range from mild to severe and may include swelling or itching of the mouth or throat, hives, itchy eyes, shortness of breath, nausea, diarrhea, cramps, and anaphylaxis. People who test negative for this condition may still have gluten sensitivity. This condition is most often seen in children, which most outgrow by adulthood.
- Dermatitis herpetiformis (DH)—A skin rash that results from eating gluten. It is an autoimmune response that exhibits itself as a persistent red itchy skin rash that may produce blisters and bumps. Although people with celiac disease may have DH, the reverse is not always true.
It is important to note that gluten is a problem only for those who react negatively to it, or test positive for celiac disease. Most people can and have eaten gluten most of their lives, without any adverse side effects.
Does gluten cause brain fog?
But does this side effect occur in people without a true gluten intolerance, and can the reverse be suggested in that the avoidance of gluten might sharpen the mind? A large cohort study disagrees. Almost 13,500 middle-aged women from the Nurses’ Health Study II without celiac disease were followed for 28 years to observe any potential links between gluten intake and mental ability.  No significant differences were found in cognitive scores (measuring reaction time, attention, memory, etc.) comparing women with the highest and lowest gluten intakes. The lack of association remained even after excluding women with a dementia or cancer diagnosis.
Unless a person has diagnosed celiac disease, a wheat allergy, or a gluten sensitivity, current evidence does not support that eating gluten increases inflammation in the brain or negatively affects brain health.
What Is a “Gluten-Free Diet”?
This is essentially a diet that removes all foods containing or contaminated with gluten. However, since gluten-containing whole grains contain fiber and nutrients including B vitamins, magnesium, and iron, it’s important to make up for these missing nutrients. Along with consuming naturally gluten-free foods in their whole form like fruits, vegetables, legumes, nuts, seeds, fish, eggs, and poultry, the following whole grains are also inherently gluten-free:
- Brown, black, or red rice
- Gluten-free oats
It’s also key not to rely on processed gluten-free foods that may be high in calories, sugar, saturated fat, and sodium and low in nutrients, such as gluten-free cookies, chips, and other snack foods. Often, these foods are made with processed unfortified rice, tapioca, corn, or potato flours.
The gluten-free food industry has grown 136% from 2013 to 2015 with almost $12 billion in sales in 2015. Interestingly, studies show that people who do not have celiac disease are the biggest purchasers of gluten-free products.  Consumer surveys show that the top three reasons people select gluten-free foods are for “no reason,” because they are a “healthier option,” and for “digestive health.”  For those who are not gluten-intolerant, there is no data to show a specific benefit in following a gluten-free diet, particularly if processed gluten-free products become the mainstay of the diet. In fact, research following patients with celiac disease who change to a gluten-free diet shows an increased risk of obesity and metabolic syndrome. This could be partly due to improved intestinal absorption, but speculation has also focused on the low nutritional quality of processed gluten-free foods that may contain refined sugars and saturated fats and have a higher glycemic index. [13,14]
- Lebwohl B, Cao Y, Zong G, Hu FB, Green PHR, Neugut AI, Rimm EB, Sampson L, Dougherty L, Giovannucci E, Willett WC, Sun Q, Chan AT. Long term gluten consumption in adults without celiac disease and risk of coronary heart disease: prospective cohort study. BMJ. 2017 May 2;357:j1892.
- Liu S, Stampfer MJ, Hu FB, et al. Whole-grain consumption and risk of coronary heart disease: results from the Nurses’ Health Study. Am J Clin Nutr. 1999;70:412-9.
- Mellen PB, Walsh TF, Herrington DM. Whole grain intake and cardiovascular disease: a meta-analysis. Nutr Metab Cardiovasc Dis. 2008;18:283-90.
- de Munter JS, Hu FB, Spiegelman D, Franz M, van Dam RM. Whole grain, bran, and germ intake and risk of type 2 diabetes: a prospective cohort study and systematic review. PLoS Med. 2007;4:e261.
- Johnsen, N.F., et al. Whole-grain products and whole-grain types are associated with lower all-cause and cause-specific mortality in the Scandinavian HELGA cohort. British Journal of Nutrition, 114(4), 608-23.
- Neyrinck, A.M., et al. Wheat-derived arabinoxylan oligosaccharides with prebiotic effect increase satietogenic gut peptides and reduce metabolic endotoxemia in diet-induced obese mice. Nutr Diabetes. 2012 Jan; 2(1): e28.
- Tojo, R., et al. Intestinal microbiota in health and disease: role of bifidobacteria in gut homeostasis. World J Gastroenterol. 2014 Nov 7;20(41):15163-76.
- Beyond Celiac. Celiac Disease: Fast Facts https://www.beyondceliac.org/celiac-disease/facts-and-figures/ Accessed 4/1/2017.
- Riddle, M.S., Murray, J.A., Porter, C.K. The Incidence and Risk of Celiac Disease in a Healthy US Adult Population. Am J Gastroenterol. 2012;107(8):1248-1255.
- N., Freeman, H.J., Thomson, A.B.R. Celiac disease: Prevalence, diagnosis, pathogenesis and treatment. World J Gastroenterol. 2012 Nov 14; 18(42): 6036–6059.
- Topper A. Non-celiacs Drive Gluten-Free Market Growth. Mintel Group Ltd. Web. http://www.mintel.com/blog/food-market-news/gluten-free-consumption-trends. Accessed Mar 27, 2017.
- Reilly, N.R. The Gluten-Free Diet: Recognizing Fact, Fiction, and Fad. The Journal of Pediatrics. Volume 175, August 2016, pages 206–210.
- Tortora, R., et al. Metabolic syndrome in patients with celiac disease on a gluten-free diet. Aliment Pharmacol Ther. 2015 Feb;41(4):352-9.
- Kabbani, T.A., et al. Body mass index and the risk of obesity in coeliac disease treated with the gluten-free diet. Aliment Pharmacol Ther. 2012 Mar;35(6):723-9.
- Wang Y, Lebwohl B, Mehta R, Cao Y, Green PHR, Grodstein F, Jovani M, Lochhead P, Okereke OI, Sampson L, Willett WC, Sun Q, Chan AT. Long-term Intake of Gluten and Cognitive Function Among US Women. JAMA Netw Open. 2021 May 3;4(5):e2113020. Disclosures: B Lebwohl reported receiving personal fees from Takeda and Kanyos outside the submitted work. OI Okereke reported receiving royalties from Springer Publishing outside the submitted work and receiving honoraria from the AARP for participation at the Global Council on Brain Health meetings. AT Chan reported receiving personal fees from Pfizer, Boehringer Ingelheim, Bayer Pharma, and Zoe Global outside the submitted work.
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