Gluten, a storage protein in wheat, rye, and barley, triggers inflammation and intestinal damage in people with celiac disease. People with intestinal or extra-intestinal symptoms triggered by gluten but who do not meet formal criteria for celiac disease may have non-celiac gluten sensitivity, a clinical entity with an as yet uncharacterized biological basis. Celiac disease, which is present in 0.7% of the US population, is associated with an increased risk of coronary heart disease, which is reduced after treatment with a gluten-free diet.
Based on evidence that gluten may promote inflammation in the absence of celiac disease or non-celiac gluten sensitivity, concern has arisen in the medical community and lay public that gluten may increase the risk of obesity, metabolic syndrome, neuropsychiatric symptoms, and cardiovascular risk among healthy people.
As a result, diets that limit gluten intake have gained popularity. In an analysis of the National Health and Nutrition Examination Survey (NHANES), most people adhering to a gluten-free diet did have a diagnosis of celiac disease. Moreover, in a follow-up analysis of NHANES, adopting a gluten-free diet by people without celiac disease rose more than threefold from 2009-10 (prevalence 0.52%) to 2013- 14 (prevalence 1.69%).
The consumption of gluten-free foods has significantly increased over the last 30 years. More than $15.5 billion were spent on retail sales of gluten-free foods in 2016, which is more than double the amount spent in 2011. The rapid rise in the popularity of a gluten-free diet (GFD) and gluten-free foods has been driven by multiple factors, including social and traditional media coverage, aggressive consumer-directed marketing by manufacturers and retail outlets, and reports in the medical literature and mainstream press of the clinical benefits related to gluten avoidance.
A lifelong gluten-free diet is well recognized as the standard of care for patients with gluten-related diseases such as celiac disease and gluten ataxia, in which immune-mediated inflammatory responses to gluten proteins are directed primarily against the small intestinal mucosa and cerebellar Purkinje fibers, respectively. Immunoglobulin (Ig) E–mediated wheat allergy is another relatively rare gluten-related disease that requires the restriction of wheat from the diet. However, people without these well-defined clinical entities have embraced a gluten-free diet due to perceived health benefits or because of a belief that gluten ingestion leads to harmful or bothersome effects.
The avoidance of gluten has extended to the population of healthy individuals who believe that adhering to a gluten-free diet may have immediate health benefits or may prevent the development of future diseases. These individuals have been described broadly as People Who Avoid Gluten (PWAG) and comprise most people who are partaking in a gluten-free diet. Such people may seek to cut back or eliminate gluten due to symptoms that have not been proven to arise due to gluten ingestion, or they may be asymptomatic.
This population either seeks to obtain benefit from symptoms without a confirmed diagnosis of a gluten-specific disorder, or these patients may seek some other benefit from a gluten-free diet rather than improvement in any specific symptom. One impetus for the practice of gluten avoidance in this population may be the perception that a GFD is a nutritionally healthier option than a traditional Western diet. Another potential perceived benefit of a gluten-free diet is that it is associated with weight loss.
Some athletes have advocated for a GFD to enhance performance and stamina. In a 2015 questionnaire-based study of 910 athletes without celiac disease, 41 % reported following a GFD more than 50 % of the time.
Potential Harms of a Gluten-Free Diet
Gluten-containing foods make up a large component of several diets, including the Western diet. These foods are relatively easy to cultivate and prepare and represent readily available and cost-friendly options to meet the caloric demands of large populations. Gluten is also a common additive to prepared foods due to its physical properties and palatability. With the popularity of GFDs, it is essential to understand the nutritional quality, potential costs, and availability of this diet and the effects that excluding gluten can have on the population and food industry.
- Nutritional Quality of a Gluten-Free Diet (GFD)
Several studies have evaluated the nutritional quality of a Gluten-Free Diet directly compared to a gluten-containing diet. Clinical outcomes data related to the effects of a GFD are sparse and inconsistent.
Some studies have shown that many gluten-free foods are not enriched and may be deficient in several nutrients, including dietary fiber, folate, iron, niacin, riboflavin, and thiamine. Other studies evaluating the nutritional composition of processed gluten-free products have demonstrated higher levels of lipids, trans fat, protein, and salt compared to their gluten-containing counterparts.
A study examined a large group of non–celiac disease men and women from the Health Professionals Follow-Up Study and the Nurses’ Health Study, respectively, and assessed patients with low-, medium-, and high-gluten consumption based on food diaries. The aim was to identify whether gluten consumption was associated with coronary heart disease. The authors found an inverse relationship between coronary artery disease outcomes and fatal and nonfatal myocardial infarctions with gluten intake.
The avoidance of gluten may reduce the consumption of beneficial whole grains, which may affect cardiovascular risk. The promotion of gluten-free diets among people without celiac disease should not be encouraged.
Financial Cost of a Gluten-Free DietStudies have shown that gluten-free alternatives are more expensive than their gluten-containing counterparts. A study in Austrian stated that gluten-free foods were also substantially higher in cost than their gluten-containing counterparts; cereals and bread and bakery products were upwards of 205% and 267% more expensive, respectively, than similar gluten-containing products.
- Social and Psychological Impact of a Gluten-Free Diet
In addition to the increased financial costs of a Gluten-Free Diet, there are other costs that can be more difficult to quantify, such as socio-psychological impacts. The pleasurable and communal aspects of food are powerful, deep-rooted perceptions embedded in individuals and society. A Gluten-Free Diet requires persistent dedication to a restricted diet and lifestyle, possibly contributing to social isolation and negative psychosocial impacts. The difficulty in maintaining adherence to a Gluten-Free Diet may also cause negative feelings and emotions in an individual, especially if he or she is non-compliant.
The Gluten-Free Diet continues to trend in popular culture and the media. More people are restricting gluten from their diet. The medical community must seek to provide an evidence-based approach delineating both the benefits and potential harms of a Gluten-Free Diet. Although convincing evidence is available to support the benefits of a Gluten-Free Diet for specific patient populations without a gluten-related disease (especially patients with irritable bowel syndrome (IBS) and nonceliac gluten sensitivity (NCGS)), the data are conflicting and not definitive. It appears that most individuals who participate in a Gluten-Free Diet do not have a physiologic requirement for the diet and likely do not derive substantial benefit. Existing evidence for potential harms of a Gluten-Free Diet includes possible nutritional deficiencies, financial costs, and adverse psychosocial implications. As with other dietary interventions, a GFD is a rapidly evolving topic. Additional insight is needed to guide a complete discussion between patients considering a GFD and their health care providers.