Maybe It’s Not the Gluten
Commentary published in JAMA Internal Medicine, November 2016
Recent consumer surveys indicate that a gluten-free diet has become one of the most popular health food trends in the United States, such that 1 in 5 individuals have eliminated or reduced gluten in their daily diet, a number that far exceeds the small subgroup that carries a diagnosis of celiac disease or IgE-mediated wheat allergy.1 In this issue, Kim et al2 report the results of their analysis of data from the National Health and Nutrition Examination Survey (NHANES), reporting that the prevalence of celiac disease has remained relatively stable from 2009 through 2014, although the prevalence of individuals reporting adherence to a gluten-free diet has more than tripled (0.52% in 2009-2010 to 1.69% in 2013-2014).
Part of what may be driving this gluten-free diet trend is simply a belief, fueled by marketing and media, that these foods are healthier. However, surveys suggest that many individuals who adhere to a gluten-free diet believe that the exclusion of gluten has resulted in subjective health benefits from weight loss to reduced symptoms of inflammation and gastrointestinal distress.3,4 Because a gluten-free diet may have negative social, financial, and health repercussions, it is important for clinicians to understand whether, in most cases, it is the elimination of the protein gluten that is responsible for symptom improvement or whether following a gluten-free diet is simply a marker of other dietary choices that are creating positive effects.5
Not all research has found that individuals who adhered to a gluten-free diet resulted in subjective health benefits. A recent 2-year prospective study6 from Italy suggests that something other than gluten itself is resulting in self-reported health benefits. Researchers enrolled all consecutive patients with gluten-related symptoms, and after those with celiac disease or wheat allergy were eliminated, only 7.5% experienced any change of symptoms with a gluten-free diet. Studies such as this raise the question of what other than gluten might explain the symptomatic improvement experienced among those following a gluten-free diet.
One explanation is that it is not the gluten but the grain itself. Researchers in Australia found that that the fermentable oligosaccharides, disaccharides, monosaccharides, and polyols (FODMAPs) and insoluble fiber that are found in gluten-containing foods may be responsible. FODMAPS and insoluble fiber increase the osmotic pressure in the large intestine and promote bacterial fermentation, which results in gas production and abdominal bloat. In a controlled, crossover study7 of patients with irritable bowel syndrome, a diet low in FODMAPs effectively reduced these symptoms; in a related study,8 patients who improved while following a low-FODMAP diet experienced no exacerbation of symptoms when gluten was introduced.
Another explanation is that gluten elimination may accompany other dietary trends that are associated with improved symptoms. For example, adherents to the popular Paleolithic and autoimmune protocol diets might also report being on a gluten-free diet.9 There is a debate about whether these diets, which promote eating unprocessed foods that were available in preagricultural times while avoiding grains, oils, and legumes, offer any health advantage over other whole food diets (such as the Mediterranean diet). Nonetheless, some have argued that simply eliminating highly processed foods (including highly processed gluten-containing foods) might result in an improved sense of well-being.
Following a gluten-free diet likely means different things to different people, and a heterogeneous group of individuals are adhering to this dietary trend. Although the choice to be gluten free may be driven in part by marketing and a misperception that gluten free is healthier, it is important that this choice not be dismissed as an unfounded trend except for those with celiac disease and wheat allergy. Instead, researchers and clinicians can use this as an opportunity to understand how factors associated with this diet affect a variety of symptoms, including gastrointestinal function, cognition, and overall well-being.
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Corresponding Author: Daphne Miller, MD, Department of Family and Community Medicine, University of California, San Francisco, 1157 Cragmont Ave, Berkeley, CA 94708 (firstname.lastname@example.org).
Published Online: September 6, 2016. doi:10.1001/jamainternmed.2016.5271
Conflict of Interest Disclosures: None reported.
1.Riffkin R. One in five Americans include gluten-free foods in diet. Gallup Inc. http://www.gallup.com/poll/184307/one-five-americans-include-gluten-free-foods-diet.aspx. Published July 23, 2015. Accessed June 12, 2016.
2.Kim H-s, Patel KG, Orosz E, et al. Time trends in the prevalence of celiac disease and gluten-free diet in the US population: results from the National Health and Nutrition Examination Surveys 2009-2014 [published online September 6, 2016]. JAMA Intern Med. doi:10.1001/jamainternmed.2016.5254.
3.Nielsen Co. We are what we eat: healthy eating trends around the world. http://www.nielsen.com/us/en/insights/reports/2015/we-are-what-we-eat.html. Published January 20, 2015. Accessed June 12, 2016.
4.Hartman Group. Gluten free trends. http://www.hartman-group.com/hartbeat-acumen/120/gluten-free-trend. Accessed June 12, 2016.
8.Biesiekierski JR, Peters SL, Newnham ED, Rosella O, Muir JG, Gibson PR. No effects of gluten in patients with self-reported non-celiac gluten sensitivity after dietary reduction of fermentable, poorly absorbed, short-chain carbohydrates. Gastroenterology. 2013;145(2):320-328.e1, 3.PubMedGoogle ScholarCrossref
9.Genoni A, Lyons-Wall P, Lo J, Devine A. Cardiovascular, metabolic effects and dietary composition of ad-libitum Paleolithic vs. Australian guide to healthy eating diets: a 4-week randomised trial. Nutrients. 2016;8(5):314.PubMedGoogle ScholarCrossref