There is a simple reason we strongly promote science-based medicine – it results in the best outcomes for individuals. That is true by definition, since the SBM approach is to use the best evidence and science available in order to determine which interventions result in the best outcomes.

There are numerous ways in which relying upon poor-quality evidence or invalid methods for making health decisions cause potential harm. Often the list is unimaginatively limited to direct physical harm, but that is only the tip of the iceberg. There is financial harm, loss of opportunity to pursue more effective interventions, psychological harm from false hope and being deceived, and sacrifice of quality of life, time, and effort.

Even without direct physical harm, with inert treatments like homeopathy, there is tremendous potential harm from relying upon fake medicine and bad science. But often there is potential physical harm, and even if slight it is not justified if there is no real benefit. Medicine is a game of risk vs benefit – when the benefit is essentially zero, any risk is unacceptable.

The gluten-free fad

Even a small potential harm can be significantly magnified if it is marketed to the general public. The “clean eating” movement, in my opinion, clearly represents such a case. The best overall advice we can give the public regarding healthy eating is to eat a variety of food with plenty of fruits and vegetables and watch overall caloric intake. Unless you have special medical considerations, simply eating a good variety of different kinds of food will take care of most nutritional concerns. It will result in you getting enough of what you need and not too much of anything that can increase your risk.

Having a restricted or narrow diet is always tricky, and runs the risk that you will be getting too little of some key nutrients and may be getting exposed to too much of others. This is the key risk of so-called “fad” diets, because they are often premised on a simplistic notion that specific foods or categories of foods are inherently bad and should be avoided. Therefore any diet which essentially consists of avoiding certain foods or heavily relying on others is likely to take you away from an optimal diet, and therefore be a net negative for your health.

The recent gluten-free fad is no exception.

As I discuss in detail here, gluten is a composite of two proteins found in wheat, rye, barley, spelt, and related grains. About 1% of the population has an autoimmune reaction to one of the components of gluten (usually gliadin) and eating gluten can cause serious illness (a condition known as celiac disease). For those with celiac disease, avoiding gluten is essential and even a small amount of gluten can cause serious symptoms.

There is a controversy, however, surrounding the alleged existence of so-called non-celiac gluten sensitivity (NCGS). This is a hypothetical condition in which people may have a sensitivity to gluten without forming antibodies to gliadin or meeting the diagnostic criteria for celiac disease. Discovering a new disease is always complex, and requires the identification of something definitive and discrete. We either need to identify a clear clinical syndrome, or some new specific pathology.

For NCGS there is no clear pathology. The entity’s legitimacy currently relies on the alleged existence of individuals who do not have celiac disease but have a negative reaction to eating gluten. If, however, we are going to base a new disease purely on clinical history, we need to make sure that the history is accurate and that we are not simply overinterpreting non-specific symptoms or falling victim to confirmation bias.

For example, there are people who feel they have a specific syndrome of sensitivity to electromagnetic waves, despite the absence of any identifiable pathology. However, properly blinded studies show that self-identified sufferers of EM sensitivity cannot tell when they are being exposed to EM waves in a blinded condition.

For alleged NCGS the most salient evidence of its existence as a clinical entity are rechallenge studies. In these studies subjects are challenged with either gluten or placebo, then the gluten is removed, and then they are later rechallenged. If NCGS is a real entity then their symptoms should resolve when gluten is removed and then return when rechallenged, at a higher frequency when the same is done with a placebo.

A recent systematic review of gluten rechallenge studies did not find significant evidence for NCGS. They conclude:

The prevalence of NCGS after gluten re-challenge is low, and the percentage of relapse after a gluten or a placebo challenge is similar.

This is a pattern of evidence that is consistent with the null hypothesis, that NCGS does not exist – results are all over the place, with better-controlled studies tending not to show an effect, and on average there is only a tiny signal that does not reach statistical significance. The most parsimonious interpretation of available evidence, therefore, is that NCGS does not exist. Despite this fact, roughly one third of the population report that they are trying to avoid gluten.

What’s the harm

What, then, is the potential harm from restricting gluten from the diet in the millions of people who do not have gluten sensitivity? Potentially, all of the things I listed above may contribute to harm.

For many people they have settled on gluten sensitivity to explain real symptoms they may be having. In this case they may be missing the real cause of their symptoms. There is therefore an opportunity cost of making a false diagnosis.

Perhaps most significantly, a gluten-free diet is very difficult. You have to eliminate all wheat and similar grains from the diet. This has become somewhat easier recently as industry is cashing in on the gluten-free fad, but it is still a significant inconvenience and expense and therefore drain on quality of life.

Further – a gluten free diet eliminates a major category of food from the diet. People on a low or gluten-free diet tend to also be low in whole grains. They risk being deficient in iron and folic acid. A recent study linked low-gluten diets to a higher risk of type-II diabetes.

Avoidance of gluten may also result in a heavy reliance on rice as a staple grain, and this might increase the risk of heavy metal exposure. Again – having a varied diet spreads out exposure to contaminants and toxins as well as maximizing exposure to needed nutrients.

Science over marketing

If we take a scientific approach to the question of NCGS we find that there is no clear evidence that non-celiac gluten sensitivity is a real thing, and that gluten-free diets not only have no benefit for the general public they present health risks. Clearly, however, we need to do a better job of communicating this to the public.

Part of the challenge, however, is that nutritional gurus (who always seem to have something to sell) have a simple and appealing narrative to market. They tell the public that their problems are due to one bad food or type of food they just need to avoid. Or, they market of lifestyle of “clean eating” that is based on the appeal to nature and irrational fear of toxins and chemicals, rather than an even basic understanding of science and evidence.

The science-based position, however, takes time to emerge. It may take a decade or more to do the kinds of studies necessary to effective answer the question about whether or not a new hypothesized clinical entity exists. There are many types of evidence to be considered, and many sub-questions to be addressed. Over time a clear picture will tend to emerge, but in the meantime the health gurus can establish a market for their nonsense. Once their simplistic and marketable narrative gets into the public consciousness it is hard to correct.

Posted by Steven Novella

Founder and currently Executive Editor of Science-Based Medicine Steven Novella, MD is an academic clinical neurologist at the Yale University School of Medicine. He is also the president and co-founder of the New England Skeptical Society, the host and producer of the popular weekly science podcast, The Skeptics’ Guide to the Universe, and the author of the NeuroLogicaBlog, a daily blog that covers news and issues in neuroscience, but also general science, scientific skepticism, philosophy of science, critical thinking, and the intersection of science with the media and society. Dr. Novella also contributes every Sunday to The Rogues Gallery, the official blog of the SGU.