"Zonulin" is either the key to non-celiac gluten sensitivity or another false lead on a fake disease

Gluten-free diets have become all the rage in recent years. And many scientists have long been skeptical that they're actually warranted for most people.

It's true that a small fraction of people have celiac disease or other serious medical conditions that make them intolerant to gluten. No one denies that. But there's also a much larger number of people who go gluten-free thinking that it'll help them lose weight (there's no evidence for this) or because of "non-celiac gluten sensitivity."

It's that latter group that has been subject to a lot of controversy. To date, many researchers have questioned whether non-celiac gluten sensitivity — which supposedly causes everything from abdominal pain to bloating and "brain fog" — even exists. Studies, such as this one in the journal Gastroenterology, have found that many people who think they react to gluten actually don’t when tested.

Most searched diets by year and metropolitan area on Google in 2015.

Now researchers have reported a new twist to this debate. According to NPR, a new study out of the University of Bologna in Italy finds that both people with celiac disease and those who reported gluten sensitivity have much higher levels of zonulin — a gut protein that sounds like the name of a sci-fi character — when compared with healthy volunteers.

Could this be the key to understanding why some people seem to react to gluten? One hypothesis is that zonulin regulates the permeability of the digestive tract and helps fight off pathogens that enter the gut. In people with celiac disease and gluten sensitivity, gluten may trigger an overproduction of zonulin, which has implications for the autoimmune system, potentially contributing to autoimmune conditions.

But maybe it's not gluten that's making people feel ill

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Still, before anyone gets carried away, this doesn't necessarily prove that gluten sensitivity is a real thing.

For one, this study still hasn't been published; it was just presented at a conference this fall. Even the researchers behind the study cautioned about the preliminary nature of their work, noting that other studies are needed to confirm their findings. Some scientists have questioned whether leaky gut syndrome — that digestive permeability — is a real medical condition.

Meanwhile, there's long been an alternative hypothesis about gluten sensitivity: that it may not even be caused by gluten. This hypothesis suggests that people may actually be reacting to another set of carbohydrates in wheat called FODMAPs (which stands for fermentable oligosaccharides, disaccharides, monosaccharides, and polyols). In other words, it could be sugars found in wheat, and not the gluten, that may be bothering some people.

But even this research is also in the very early stages. Many of the studies involving people with gluten sensitivity or FODMAPs diets have tiny sample sizes, and the science is still working itself out.

For now, one of the leading researchers in the area, Dr. Umberto Volta from the University of Bologna, put it this way: "This is an emerging condition mainly self-reported by people who claim an association between foods containing gluten and digestive symptoms." While some self-report an improvement in symptoms when they go gluten-free, this is usually "a result of a placebo effect unavoidably related to the elimination diet." When these patients are assessed more thoroughly, he added, it's often other factors — lactose intolerance,FODMAPs — rather than gluten that cause their discomfort. Still, gluten gets the blame.