Do Millions of People Need a Gluten Free Diet?
Going gluten-free is a popular trend fueled by the media, the internet, and a sizable group of medical practitioners. This trend is based on the claim that a gluten free diet (GFD) has vast benefits for a number of disorders affecting mind and body.
Empiric gluten avoidance likely is not without negative health consequences. Avoidance of gluten from whole grains may affect the risk for type 2 diabetes mellitus, cardiovascular disease, and mortality. In addition, indiscriminate exclusion diets have even been linked to malnutrition and disordered eating behaviors.
A National Health and Nutrition Examination survey estimated that by 2014, 2.7 million US adults without celiac disease adhered to a GFD, increasing by more than 3-fold since 2009. This may be owing to gastrointestinal symptoms erroneously attributed to gluten intake, as in nonceliac gluten sensitivity. Alternatively, the GFD, popularized by the media and consumer-directed marketing, may be used by patients because of various perceived health benefits.
The economic impact of this trend is remarkable. The gluten-free products market size was valued at $4.3 billion in 2019 and is estimated to reach $7.5 billion by 2027. Gluten-free labels can now be found on almost every food product, even on water bottles and pill box labels.
While a GFD is essential for people with gluten allergies and celiac disease – a serious autoimmune disorder of the small intestine – the existence of non-celiac gluten sensitivity and its involvement in many gut and brain disorders has been challenged by a number of epidemiological studies and controlled clinical trials.
A series of large, well designed epidemiological studies from the Harvard T.H. Chan School of Public Health under the leadership of Andrew Chan has provided strong evidence refuting a role of gluten in common brain and gut disorders, or a benefit of a GFD for any serious health problem.
In a study looking at the long-term intake of gluten and cognitive function among a cohort of 13,494 women at midlife without a celiac disease diagnosis, there was no statistical evidence of any association of long- or short-term consumption of wheat, barley or rye – the major sources of gluten – and “brain fog”, a condition reflecting compromised cognitive ability. According to the study authors, the only individuals who benefitted from avoiding gluten were the small number of patients with celiac disease.
In similar studies, no evidence between gluten intake and cancers of the gastrointestinal tract or cardiovascular risk were identified. However, the authors emphasized that avoidance of gluten may result in reduced consumption of beneficial whole grains, which may affect cardiovascular risk. They recommended that the promotion of gluten-free diets among people without celiac disease should not be encouraged.
In the most recent study, the Harvard investigators aimed to examine the relationship between dietary gluten and the risk of inflammatory bowel diseases (IBD) in adults without celiac disease.
Inflammatory bowel diseases, including Crohn’s disease (CD) and ulcerative colitis (UC), are chronic inflammatory diseases of the gastrointestinal tract that are thought to result from a dysregulated immune response to environmental and microbial stimuli in a genetically susceptible host. Although several hundred gene polymorphisms have been identified, the total variance of IBD risk explained by known genetic factors is less than 14%, highlighting the significance of environmental factors in disease development. One important environmental factor is diet, likely owing to its influence on gut microbiota composition, mucosal barrier function, and mucosal inflammation.
IBD is associated with an increased risk for celiac disease, although nonceliac gluten sensitivity also is commonly reported by patients with IBD, and some patients report improvements in gastrointestinal symptoms following dietary gluten restriction. There are several possible reasons to explain such a benefit.
It may be due to the fact that these patients were suffering from undiagnosed celiac disease or by an effect of gluten on IBD disease activity. To answer these questions, the Harvard investigators explored the relationship between dietary gluten intake and the risk of IBD in 3 large prospective US cohorts of men and women. These cohorts were made up by 208,280 US participants from the Nurses’ Health Study (1986–2016), Nurses’ Health Study II (1991–2017), and by the Health Professionals Follow-up Study (1986–2016). None of the participants had a diagnosis of IBD or celiac disease at baseline, and all of whom had completed semiquantitative food frequency questionnaires.
The study identified 337 CD cases and 447 UC cases over 5,115,265 person-years of follow-up evaluation. (“Person-years” is a statistic for expressing incidence rates which is determined by the summing of the results of events divided by time).
The results showed that dietary gluten intake was not associated with an increased risk of IBD. Adjusting their results for primary sources of gluten intake did not significantly change their estimates.
When viewed together, the large, well-designed studies from the Harvard School of Public Health do not support commonly held beliefs about the detrimental effects of gluten consumption on cognitive function and gut health. Despite the impressive numbers of participants in the mentioned studies, there are limitations such as their epidemiological nature and the reliance on food frequency questionnaires to assess gluten intake. However, they point out the dangers of avoiding gluten in the diet and emphasize the considerable economic cost and lifestyle limitations that are associated with a restricted diet, that is often not based on scientific evidence but rather on food related fears.
Dr. Emeran Mayer is a Distinguished Research Professor in the Departments of Medicine, Physiology and Psychiatry at the David Geffen School of Medicine at UCLA and the Executive Director of the G. Oppenheimer Center for Neurobiology of Stress and Resilience at UCLA.