The fashionable gluten-free diet-wear with caution.

Olympic gold medalist in swimming Dana Vollmer, the current men’s world top-ranked tennis player Novak Djokovic, 6-time Olympian Nordic combined skier Todd Lodwick, and National Football League quarterback Drew Brees are just a few examples of world-class athletes who have adopted and touted the benefits of the gluten-free diet (GFD). Riding the wave of these athlete and other celebrity endorsements, the diet has become extremely popular. In addition, the expanding gluten-free product market is making it more accessible to the general public. Although initially designed for those with celiac disease, dermatitis herpetiformis, and wheat allergy, the GFD is followed by many without celiac disease or other diagnosed gluten-related disorders. Its rise in popularity has outpaced even the growing incidence of celiac disease. We review who is following a GFD and why, how it complicates celiac disease diagnosis, and the diet’s health benefits and harms. The percentage of people without celiac disease avoiding gluten (so-called PWAGs) in the United States is 1.1% according to NHANES data (1). In Australia, 7.3% of surveyed participants without celiac disease avoid wheat to some degree (2). In the United Kingdom, that number is 1.4% (3). A minority of individuals following a GFD have celiac disease, an immunemediated response to dietary gluten resulting in villous atrophy and malabsorption of nutrients in the small intestine. Lifelong GFD is the gold standard for treatment and the only established remedy for celiac disease (4). Besides celiac disease, individuals cite various reasons such as nonceliac gluten sensitivity for adhering to this diet (although the role of gluten remains controversial), and gluten has been blamed as the culprit for innumerable health complaints. The study in this issue of the American Journal of Clinical Nutrition by Littlejohns et al. (3) used the UK biobank to characterize those following a GFD. In their population-based study, they excluded 853 participants with celiac disease and identified 1776 participants following a GFD—nearly twice as many as those with a medical diagnosis necessitating gluten exclusion out of a sample of 124,447 (3). They found that nonwhite women who were highly educated with poorer selfrated health were most likely to follow a GFD (3). Participants who used to drink or smoke and had made positive life changes with weight loss, perhaps showing a desire to improve their health, were more often following a GFD (3). No genetic variants were uncovered to suggest a biologic mechanism underlying this dietary choice (3). These results are congruent with American and Australian data that show women follow a GFD at higher rates than men (1, 2). Nonwhite individuals have also been reported to adopt the GFD at higher rates in the United States (5). As in earlier research, those without celiac disease far outnumber those with celiac disease who have adopted the GFD (2). Adopting a GFD prior to formal diagnosis of celiac disease is problematic since serologic and endoscopic testing then becomes unreliable. Celiac disease is screened for with a blood test for tissue transglutaminase antibody, and the diagnosis is confirmed by the finding of villous atrophy and other characteristic histologic changes in the small intestine. Patients who selfdiagnose celiac disease and avoid gluten before undergoing a medical evaluation may be reluctant to reintroduce gluten and get tested. Unaffected people may choose to follow a GFD for unclear health benefits, which creates a “gluten paradox” of one group without celiac disease following a strict diet without medical necessity and another group who could benefit substantially but is yet undiagnosed. Celiac disease is thought to affect ∼1% of the population worldwide, but research reports many are unaware of their diagnosis, and screen detection reveals numerous patients due to atypical or asymptomatic presentations (6). Following a GFD without medical advice or a formal evaluation creates challenges for physicians, undiagnosed patients, and perhaps those who have placed themselves on this unnecessarily restrictive and expensive diet. The benefits of a GFD in those without gluten-related disorders have not been definitively proven. Whether it is the celebrity athletes and their anecdotal successes after implementing a GFD or other reasons, the general public has a favorable perception of this diet as part of a healthier lifestyle. One study by DiGiacomo et al. (7) reported a higher HDL and lower BMI in those without celiac disease following a GFD. The lower BMI was verified by Tavakkoli et al. (8) for those on a GFD without celiac disease compared with controls along with lower rates of hypertension. The GFD may offer short-term benefits of alleviation of various symptoms or ailments (placebo effect? ) and, according to limited research, an improved cardiovascular risk profile, but these improvements require weighing against the potential long-term consequences of dietary elimination from a nutritional standpoint.