As I sift through the ruins of organized skepticism, I recall something that always bugged me.

Celiac disease is an autoimmune disorder that causes a bunch of chronic gastrointestinal problems.  The treatment to celiac disease is to switch to a completely gluten-free diet.  However, people with celiac are not by themselves the cause of the many gluten-free products sold in stores.  Many people buy those because they believe they have a different condition, Non-Celiac Gluten Sensitivity (NCGS).  They believe that when they go on a low-gluten or gluten-free diet, they have fewer gastrointestinal symptoms (e.g. they feel less bloated).  I say “believe”, because there is no consensus that NCGS exists.

The standard skeptic’s line on NCGS is that there is no evidence that it exists, and there is no reason for people to go on gluten-free diets unless they think they have celiac disease.  One study that has been used in support of this position, is a paper from 2013, which says in the title “No effects of gluten in patients with self-reported non-celiac gluten sensitivity“.

The interesting thing about this paper is that it says that people who report NCGS do experience a significant reduction in symptoms when they change their diet.  However, the important change in their diet is not the elimination of gluten, but the elimination of another category of chemicals, known as FODMAPs.  FODMAPs are generally present in the same grains that include gluten, so it’s easy to get them confused without having a study designed specifically to separate them.  In other words, it is possible that people who believe they have NCGS are correct about having symptoms that improve with a change in diet, but incorrect about the source of those symptoms.

I recall that back in 2013, skeptics were saying, “This is another confirmation of what we’ve been saying all along: NCGS doesn’t exist.”  And I recall reading the news reports and thinking, wait.  This means we were wrong.  People who thought they had NCGS were correct to change their diets.  We were wrong.  Why weren’t skeptics acknowledging that they had been wrong?

A few caveats.  The 2013 study only involved 37 participants who self-reported NCGS.  I wouldn’t take its conclusions for granted without further study.  Since I do not follow this literature, all I can say is that I’m unaware of further studies that either reproduced or overturned the conclusions.  If any readers are aware of such studies, you are welcome to share in the comments.  But as far as I’m concerned, the idea that self-reported NCGS can be attributed to FODMAPs rather than gluten, is merely a hypothesis with some support.  I should also mention that the study did in fact find a non-zero effect of gluten:

Gluten-specific effects were observed in only 8% of participants.

In other words, they did in fact measure gluten sensitivity in a few of the participants, but it happened in so few cases that it was not statistically significant enough to reject the null hypothesis.  While I agree with the authors that this does not constitute evidence of NCGS, I think it drives home the point that 37 participants isn’t really enough.  If it were true that <8% of people who think they have NCGS really do have it, then you’d need a more powerful study to detect evidence of that.

But for the moment, let’s take for granted the conclusions of the study (just as skeptics did).  The study suggests that in ordinary circumstances, people who believe they have NCGS can improve their health by eliminating wheat and other grains from their diet.  Furthermore, the effect is so significant that it can be detected in a clinical study with only 37 participants.  However, there are some changes in diet which will not help.  In particular, if you somehow eliminate gluten-containing grains, while maintaining a high FODMAP diet, there may be no improvement at all.

There’s an important followup question.  While avoiding gluten-containing grains will also lead to a low-FODMAP diet that will improve some people’s health, it is less clear to me that products advertised as “gluten-free” would do the same.  For all I know, these products have substituted gluten-containing grains for some ingredient that does not contain gluten but is high in FODMAPs.  I have no idea if this is remotely true, but it seems like such a basic question.

Anyway, the study suggests that people who claim to have NCGS don’t really have it.  They aren’t sensitive to gluten, they’re sensitive to FODMAPs.  So skeptics who said NCGS doesn’t exist were technically vindicated.  But that’s missing the point.  Changing the name from NCGS to Non-Celiac Wheat Sensitivity (or whatever) is easy.  Changing diets is hard.  Skeptics can feel vindicated about a technical point of minor significance, and gluten-free dieters can feel vindicated on the part that actually matters: the benefits of the diet itself.

I have not read any of the literature on the subject and acknowledge the possibility that I have drawn the incorrect conclusion on NCGS.  However, if that is the case, then it just shows that skeptics failed to present the relevant evidence, and instead promoted a study that clearly disconfirmed their stated position.