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When you read in alternative medicine journals that there’s “a great deal of evidence that foods containing casein or gluten contribute significantly to [autism] and should be eliminated from the diet…almost always lead[ing] to symptomatic improvement,” they’re presumably talking about the published anecdotes and case series that claim wild success—but had no control group, though there were two year-long controlled trials that also showed remarkable benefits, but couldn’t discount placebo effects.

The double-blind studies that did control for placebo effects failed to find benefits, but they only lasted a few weeks. This was to be the study to break the logjam: a months-long, double-blind, controlled study. They put 14 kids with autism on a gluten-free, casein-free diet for four to six weeks, and then, for the next three months, challenged them every week with double-blind, placebo-controlled food tests, secretly giving them gluten (just gluten), or just casein—or both, or neither, every week, month after month.

Here’s what happened to each of the 14 kids in terms of their social relationships and their language skills throughout each of the challenges. And, bottom line? Nothing. No apparent impact on behavioral disturbances or autism-related behaviors. So, does that mean case closed? Well, “proponents of [autism diets] might regard the 4–6 week implementation phase prior to the challenges as too short for the [gluten-free, casein-free] diet to take full effect.” In other words, one could argue this is yet another double-blind study that didn’t give the diet long enough time to work. And so, maybe the kids were still feeling the effects of gluten and casein they consumed more than a month previously. And so, no wonder extra gluten or casein didn’t make them even worse?

It’s possible, I guess, which is why you’ll see systematic reviews of the sum total of evidence, like this one, published 2017 in the journal of the American Academy of Pediatrics, concluding that although some studies showed benefits, the “data [are] inadequate to make conclusions” either way. In other words, the “SOE”—the strength of evidence—is considered “insufficient” to endorse such diets.

What’s the harm in giving it a try, though? Well, “[g]iven the effort, time, and money that [a gluten-free, casein-free] diet requires, knowing whether” it actually works would kinda be a good thing to know. I mean, there are downsides; “being on a special diet can have unintended negative social consequences, when children are not able to participate conventionally in birthday celebrations and class treats or eat in restaurants or other people’s homes.” Autism can be isolating enough as it is.

“[T]he [overall] evidence for the effectiveness of [these diets] is weak and thus these diets cannot be generally recommended as a treatment…” Yet, parents continue to give it a try, figuring, “Look, the drugs don’t work, in terms of helping the core symptoms. So, why not just give it a try and leave no stone unturned?” I can understand that; however, there are the potential downsides, like further “stigmatization, diversion of…resources [away from other treatments],” and, they suggest, a concern about “nutritional deficiency.”

What they’re worried about is bone health. Those with autism are at elevated risk for bone fractures. Now, lower bone mineral density in individuals with autism may be due to a variety of factors: lack of vitamin D, chronic use of medications that can weaken bones, lack of weight-bearing exercise—but, maybe dietary restrictions play a role.

Do children with autism on gluten-free, casein-free diets have lower calcium intake? Yes—in fact, nine times the odds of failing to meet recommended calcium intakes. Does this translate out to reduced bone mass? Maybe so, as those on casein-free diets appeared to have less bone development. Now, there’s “controversy over whether dairy products…[are] the best source of calcium,” but that is where most kids are getting their calcium. And so, if you remove dairy, you have to replace it with other calcium-rich foods. As the study they cited points out, there’s lots of non-dairy sources of calcium—but, they only provide calcium if you actually eat them.

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