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What Makes an Expert an Expert?

An article recently appeared in the journal Headache, under the title, "Expert Opinions: Gluten-free diet and migraine." (1) The article presented a case report of a woman with migraines and alternating constipation and diarrhea. Testing for celiac disease was negative, and the woman was diagnosed with irritable bowel syndrome. After reading about gluten and migraines on social media, she went on a gluten-free diet (GFD) and reported that her migraines were less frequent. The article went on to pose several questions to a panel of "experts": Is there an association between celiac disease and migraine? Does migraine improve after going on a GFD? Does a GFD improve migraine in people who do not have celiac disease? Is there any harm to a GFD? Two of the four experts are neurologists and the directors of headache clinics. Another expert is also a neurologist specializing in headaches, and the fourth expert is a research coordinator.

These experts cited literature demonstrating that migraine is more frequent in patients with celiac disease than in controls, and that migraines usually improve in celiac patients after they go on a GFD. With regard to migraine patients who do not have celiac disease, they stated that there is little research on the subject, and that it is unclear whether a GFD is beneficial. In the "Conclusion" section of the article, they were somewhat more negative, stating that... "a GFD is only significantly beneficial to patients diagnosed with CD [celiac disease]." They further argued that a GFD is potentially harmful because it can lead to weight gain, which may exacerbate migraines and increase the risk of various diseases associated with obesity.

I am certain that few, if any, headache specialists would consider me an expert on migraines. However, I am nearly as certain that the experts who wrote this report are incorrect in asserting that there is little or no evidence a GFD can prevent migraines in non-celiac patients. It is difficult to ignore the many patients I saw over the years who were firmly convinced that wheat (the major gluten grain) was a trigger for their migraines. And the observations of my patients are supported by a number of published studies. In Grant's landmark 1979 paper in Lancet, 60 patients with a long history of frequent migraines underwent an elimination diet followed by individual food challenges. Seventyeight percent of the patients were found to react to wheat. When all symptom-evoking foods were removed from the diet, 85% of the patients became headache-free, and the total number of headaches per month in the group as a whole fell by 98.5%. (2) In a 1983 study of 88 children with severe frequent migraines, an elimination diet resulted in complete resolution of migraines (n = 78) or marked improvement (n = 4) in 93% of cases. Of the 82 children who had a positive response to the diet, 21 (25.6%) reacted to wheat. (3) In a 1955 report, of 45 patients with migraines, nine (20%) found on elimination-and-rechallenge testing that wheat triggered attacks. (4)

For two reasons, I suspect that the experts who wrote the report in Headache have little or no experience with elimination diets. First, based on the medical literature, as well as my clinical experience and that of many other nutrition-oriented practitioners, it seems implausible that anyone who routinely investigates food allergies and sensitivities could come to the conclusion that the role of wheat as a trigger is "unclear." Second, the experts implied in the article that people who suspect gluten sensitivity is contributing to their migraines should consult a nutritionist.

In addition, the experts' statement that GFDs cause weight gain is open to debate. They did not provide a reference for that statement, but they did mention that the study included 679 patients with celiac disease. A search of PubMed revealed only one study that enrolled 679 patients and assessed the effect of a GFD on body mass index (BMI) in people with celiac disease. Mean BMI did increase to a small extent (from 24.0 kg/[m.sup.2] to 24.6 kg/[m.sup.2]) over a mean follow-up period of 39.5 months, after the patients went on a GFD. However, celiac disease is associated with malabsorption, which can cause some patients to be underweight or have a low-normal BMI. In those people an increase in BMI is probably a good thing. When considering only those people in the study who were overweight or obese at baseline, the number who had a BMI decrease of at least 2 points was similar to the number who had an increase of at least 2 points. (5) Another study found that when patients with celiac disease went on a GFD, 66% of those who were underweight gained weight. In contrast, among those who were obese, 47% lost weight and only 18% gained weight. Among those who were overweight, 54% lost weight and 40% gained weight. (6)

If various headache specialists are wrong about issues related to gluten and migraines, and if they provide a somewhat unbalanced view of the effect of GFDs on BMI, why are they considered experts in these areas? As a first step in trying to answerthattroubling philosophical question, I looked up the word "expert" in the dictionary. I learned that an expert is "a person who has a comprehensive and authoritative knowledge of or skill in a particular area." So, then I looked up "authoritative," which means "able to be trusted as being accurate or true." Which begs the question: why should someone who went through a specialty training that likely ignored the role of food allergy in migraines, and then practiced that specialty while continuing to ignore the role of food allergy in migraines, be considered an expert on the role of food allergy in migraines?

Modern medicine has a long history of equating credentials with expertise, but these things are not synonymous. This is especially true with respect to food allergy. While hidden food allergy is an important contributing factor to many symptoms and diseases in the fields of gastroenterology, cardiology, dermatology, psychiatry, rheumatology, nephrology, neurology, and otolaryngology, few specialists in these fields consider hidden food allergy in their differential diagnosis or know how to identify it.

If having credentials does not necessarily guarantee expertise, how can we know whom to trust as experts? In my 47 years in the field of nutritional medicine, I have tended to view most "expert opinions" with some degree of skepticism. If I have questions about whether the information is being presented accurately, I look up the reference citations and try to come to my own conclusions. With time, one learns that certain writers, thinkers, and researchers are quite reliable, and that their works are less likely to require fact-checking. These individuals typically undertake a comprehensive, balanced, and detailed review and analysis of the evidence; are free of obvious biases and conflicts of interest; understand the limitations of the evidence and do not over-interpret the data; and are not afraid to admit when they don't know something.

I realize that many of us do not have the time or the training to investigate each scientific question for ourselves. By necessity, much of what we learn will come from teachers and other experts. However, it is important to maintain a healthy degree of skepticism in all areas of inquiry, and to remember that credentials and university affiliations do not automatically endow someone with the truth.

Alan R. Gaby, MD


(1.) Beuthin J, et al. Expert opinions: Gluten-free diet and migraine. Headache. 2020;60:2526-2529.

(2.) Grant EC. Food allergies and migraine. Lancet. 1979;1:966-969.

(3.) Egger J, et al. Is migraine food allergy? A double-blind controlled trial of oligoanrigenic diet treatment. Lancet. 1983;2:865-869.

(4.) linger AH. Allergy and headaches. Ann Allergy. 1955;13:523-532.

(5.) Kabbani TA, et al. Body mass index and the risk of obesity in coeliac disease treated with a gluten-free diet. Aliment Pharmacol Ther. 2012;35:723-729.

(6.) Cheng J, et al. Body mass index in celiac disease. Beneficial effect of a gluten-free diet. J Clin Gastroenterol. 2010;44:267-271.
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Title Annotation:Editorial
Author:Gaby R., Alan
Publication:Townsend Letter
Date:Apr 1, 2021
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