If you're not aware, the gluten free diet is THE diet in the autism community. Those who believe in the diet believe in its benefits (claims can range anywhere from help with stomach problems, to a cure for autism) with an almost religious fervor. Given that fervor, talking about it is like talking about vaccines - it's a very dangerous thing for me to come out and discuss, because I will inevitably offend people. If you are one of those people, please know that is not my intention, nor is it a reflection of my respect for you or your decision. I write merely to spread information.
Discussing the gluten free diet is difficult for me, because I admit, I don't have a full understanding of all the literature. I have read quite a few studies (straight from the source, not merely blog articles that pick and choose and twist studies merely to support their points), mind you, but I am not an expert in the area. It is even more difficult for me to write here, because it's hard for me to address all the claims made about the gluten free diet, since they are so numerous. So instead, I'll break it down into the four most common claims, and then go into the reasoning/research behind the scenes.
1. Does a gluten free diet cure autism?
No. At this point in time there is no cure for autism.
2. Does gluten cause autism?
No. I'm sure I could go in depth and explain scientific reasons for why it doesn't, but we'll just stick with common sense here. Studies have found symptoms of autism in babies as far back as early infancy - at which point the baby isn't eating anything with gluten.
3. Does the gluten free diet significantly reduce any symptoms of autism?
Maybe, but it's unlikely. Studies disagree here, but the most trustworthy scientific take on this I've found - a Cochrane review - says there's "a lack of evidence to support the use of gluten and/or casein free diet as an effective intervention for persons with autism and also a lack of research on potential harms and disbenefits of such diets." Even without the review, though, between the biases involved and confounding variables, I'm extremely doubtful that there's any causal relationship.
4. Can the gluten free diet help some people with gastrointestinal problems?
Yes. I speak here as someone who is currently on a gluten free diet, as prescribed by my gastroenterologist for gut issues. I can personally attest to it, and there are loads of studies to back this up.
Okay, so I mentioned confounding variables in number three as a problem and I may have lost some of you. What is a confounding variable?* Well, in this case we're talking about the third variable problem, which is what happens when an outside variable makes it seem like there might be a causal relationship between two things, when there really isn't. For instance, using statistics, I could make it seem like ice cream causes people to drown. Because, and this is true, as ice cream consumption increases, so do drowning deaths. Does ice cream cause people to drown, though? No, of course not! There's another factor in there - heat. As it gets hotter, people seek relief by eating ice cream...and going swimming. Therefore, while it's true there's a relationship between the two, it isn't causal. There's a third variable, heat, which explains their correlation. This, by the way, is one of the reasons you should always be cautious when you read a headline that declares there's a correlation between ____ and autism, because for reasons such as the third variable problem, correlation does not prove causation.
What is a possible confounding variable in all this autism and gut problems research? Well, the biggest one, which was my automatic thought when I heard about this potential relationship, is anxiety. Anxiety is a highly comorbid problem for autistic people, which is to say that anxiety and autism are related. Anxiety and gut problems are also related. Therefore, you have a potential third variable. Anxiety could be causing these gut problems that we're seeing, as opposed to autism.
Another potential confounding variable is the food restrictions of people on the spectrum. Many are 'picky eaters' who have a very limited diet as a result. A diet inadequate in nutrition can, as Willingham points out, cause the very gut problems that the gluten free diet (for some) seeks to remedy. So, ironically, curtailing someone's diet by eliminating anything with gluten could also be causing harm. For this reason, I highly recommend utilizing a nutritionist if you choose to try the gluten free diet.
Yet another variable, which could help explain the occasional (still not as large as it has been painted) change in some symptoms in some autistic people, but not in all** that some (but again, not all) studies have found is gastrointestinal in nature. After all, if you're in pain and having gastro trouble, and then all of a sudden that pain/discomfort goes away, it's pretty common sense that your behavior is going to improve as well. Teasing out the difference between the two effects is something we have to be careful to do.
Why is it important whether or not gluten causes the dietary issues? Well, we could be focusing on this at the wrong angle. If, as I suspect, anxiety is the culprit, we could be focusing our attention on interventions to help combat it directly, while preserving dietary variety, which, as I said, is particularly important for picky eaters. Caley swears by anxiety medication for herself, but says we should be focusing even more on teaching people with anxiety techniques to help them cope...which we don't do. If battling anxiety were embraced with the same fervor as the gluten free diet has been, I feel quite certain that autistic people (and their guts) would be better off.
Now, I am not a scientist. I have pretty extensive training in statistics and a fair amount in research methods, which is why I feel more comfortable interpreting these studies than most, but I am definitely not a professional in the field. (Willingham, however, is.) I also have not done as much in-depth research into this issue as I would like and cannot say anything with certainty. The gluten free diet may well work to alleviate certain symptoms of autism, though again, given the weakness of the evidence at the moment, I am doubtful.*** I am fairly confident that it can help with gut problems that many autistic people have, but whether or not it helps on the net, when you factor in potential inadequate nutrition, or whether it helps more than targeting anxiety, I cannot say.
One thing, however, I am absolutely confident about. The gluten free diet is not the miracle 'cure' for autism or even for certain symptoms that it's been painted to be, and if I had an autistic child without obvious gastrointestinal issues, given current evidence, I would not be putting them on this diet.
*I'm simplifying my explanation to the extreme here, so those of you scientists/statisticians, go easy on me.
**Note how many qualifiers I included here. Occasional (as in, not all studies found these changes - I haven't examined the study construction in depth so I can't say if that might have something to do with the discrepancies), subset (as in, only a small sub group of people studied showed any such potential changes), and only some of the symptoms changed and not by huge amounts (as in, it's not a fix for those symptoms).
***I am speaking to the perspective of parents of autistic children who would put them on the GF diet, here. Myself and Caley don't see it as symptoms separate from the person, merely characteristics that autistic people often share, and we don't see them as the problem others do.