What did the most comprehensive double-blind study of diet for autism find, and what are the potential downsides? When you read in alternative medicine journals that there is “a great deal of evidence that foods containing casein or gluten contribute significantly to ASD [autism spectrum disorder] and should be eliminated from the diet” and that “implementation of a strict casein- and gluten-free (CFGF) diet almost always leads to symptomatic improvement,” the authors are presumably talking about the published anecdotes and case series that claim wild success but had no control group. There were two year-long controlled trials, however, that also showed remarkable benefits, but neither could discount placebo effects. The double-blind studies that did control for placebo effects failed to find benefits, but they only lasted a few weeks.
As I discuss in my video Pros and Cons of Gluten-Free, Casein-Free Diets for Autism, researchers then conducted the study that was supposed to break the logjam: a months-long, double-blind, controlled study. Fourteen kids with autism were placed on a gluten- and casein-free diet for four to six weeks. Then, for the next three months, the researchers challenged them every week with double-blind, placebo-controlled food tests, secretly giving them “foods that contained gluten only, casein only, both gluten and casein, or neither (placebo),” every week, month after month.
Researchers analyzed what happened to each of the 14 kids in terms of their social relationships and their language skills throughout each of the challenges, which you can see at 1:13 in my video. And the findings? Nothing. No apparent impact of the “GFCF diet” was found on behavioral disturbances or autism-related behaviors. Does that mean the case is closed? Proponents of autism diets “might regard the 4–6 week implementation phase prior to the challenges as too short for the GFCF diet to take full effect.” In other words, one could argue this was yet another double-blind study that didn’t give the diet a long enough time to work. Could it be that the kids were still feeling the effects of gluten and casein they had consumed before the study started, more than a month previously, which may explain why extra gluten or casein didn’t make them worse? It’s possible, I guess, which is why, from time to time, you’ll see systematic reviews of the sum total of evidence concluding that although some studies “evaluating gluten/casein-free diets” showed benefits, the data are “inadequate” to make conclusions either way. In other words, the strength of evidence is considered insufficient to endorse such diets.
But what’s the harm in giving it a try? “Given the effort, time, and money that the GFCF diet requires, knowing whether this investment will pay off”—that is, whether a gluten- and casein-free diet actually works—”would be valuable.” There are downsides. For instance, “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.
The overall “evidence for the effectiveness of GFCF diets in children with autism is weak and thus these diets cannot be generally recommended as a treatment”—yet, parents continue to give it a try, figuring, “Since the drugs don’t work in terms of helping the core symptoms, why not just give the diet a try and leave no stone unturned?” I can understand that, but there are the potential downsides, like further “stigmatization, diversion of treatment, and nutritional deficiency.” Nutritional deficiency?
The concern is about bone health, as 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, such as lack of vitamin D, chronic use of medications that can weaken bones, and lack of weight-bearing exercise. But, dietary restrictions may also play a role.
Do children with autism on gluten- and casein-free diets have lower calcium intake? Yes, in fact, they have 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 appear 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. So, if you remove dairy from the diet, you have to replace it with other calcium-rich foods. As research has shown, there are lots of nondairy sources of calcium, but they only provide calcium if you actually eat them.
Recommendations for eliminating foods containing casein or gluten to improve symptoms of ASD are often based on published anecdotes and case series without control groups.
In response, researchers conducted an extended double-blind, controlled study on children diagnosed with ASD, placing them on a gluten- and casein-free (GFCF) diet for four to six weeks, followed by three months of weekly challenges of double-blind, placebo-controlled food tests—gluten only, casein only, both gluten and casein, or neither.
No apparent impact of the GFCF diet was found on behavioral disturbances or autism-related behaviors, but critics have suggested the duration of the study wasn’t long enough and many parents and caregivers continue to try a GFCF diet in children with autism despite the lack of evidence of its effectiveness.
Downsides of a GFCF diet in children with autism include unintended negative social consequences, such as increased isolation and further “stimatization, diversion of treatment, and nutritional deficiency.”
Those with ASD are at heightened risk for bone fractures, having lower bone mineral density, which may be due to lack of vitamin D, chronic use of medications that can weaken bones, and lack of weight-bearing exercise.
Children with autism on a GFCF diet have been found to have lower calcium intake, but that may be the consequence of not replacing the calcium from dairy once milk and other dairy products are removed from the diet.
If dairy is removed from the diet, it must be replaced with other calcium-rich foods, such as nondairy calcium sources.
This is the final article on my six-part video series on the role of gluten- and dairy-free diets in the treatment of autism. If you missed any of the others, see:
Keep abreast of all of my videos on autism here.
Hold on. Milk isn’t protective against bone fractures? See Is Milk Good for Our Bones?.
For more on diet and autism, see:
Michael Greger, M.D.
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