Does it work?

The effectiveness of elimination diets in improving the behavior of children with autism has only recently been scientifically researched ⁽⁸⁾. This research has almost always examined diets that are both casein- and gluten-free.

One well-controlled study focused on children with autism who had abnormally high protein by-products in their urine, and therefore were more likely to be sensitive to casein and gluten (see What is the theory behind it?). One group of these children was fed a strict casein- and gluten-free diet for 12 months. This group had significantly fewer autistic symptoms than the remaining children, who were not fed this diet ⁽⁹⁾.

Another well-controlled study of casein- and gluten-free diets focused on children with autism regardless of the level of protein by-products in their urine ⁽¹⁰⁾. Overall, the study found no significant differences in behavior between children on the elimination diet and children on regular diets, although individual parents reported behavioral improvements ⁽¹⁰⁾. A third well-controlled study reported no significant improvements in speech for 13 children who followed a gluten-free casein-free diet for 6 weeks ⁽¹¹⁾. There were limitations in these studies, including relatively short time periods on the diet and/or small samples sizes.

Regardless, in both cases, the tested diets were casein- and gluten-free, so it is not clear whether it was the elimination of casein, gluten, or both that resulted in any improvements. A third study that did examine the effect of a gluten-free diet on the behavior of children with autism did not compare children on the elimination diet with children not on the diet ⁽¹²⁾. Therefore, even though there were improvements seen in the behavior of children on the diet, these may also have occurred over the 5 months of the study without the elimination diet

The current thinking is that there is at least some evidence showing that a gluten-free diet, when combined with a casein-free diet, can help improve the behavior of some children with autism. Although the casein-free diet combined with a gluten-free diet is popular, there is little evidence to support or refute this intervention and reviewers have determined that meaningful conclusions cannot be drawn from the existing literature ^{(3, 4)}.