For years parent support networks and celebrity activists have endorsed restrictive diets to combat the so-called "leaky gut" symptoms and behavior problems of children with autism.
But an expert panel published a report today saying there is currently no evidence proving whether children with autism have more gastrointestinal problems than other children, or any evidence that the common casein-free, gluten-free diets work.
The statement on so-called autism diets was one part of a larger report on how doctors should approach gastrointestinal issues in children with autism.
The report, published today in the journal Pediatrics, echoed some parents' claims that gastrointestinal issues are linked to autism-like behaviors.
The panel of 27 experts agreed that "problem behavior in patients with ASDs (Autism Spectrum Disorders) may be the primary or sole symptom of the underlying medical condition, including some gastrointestinal disorders."
But until studies prove or disprove the merits of casein-free and gluten-free diets, the experts recommended adapting traditional treatments for gastrointestinal problems in children with autism.
"Probably 90 percent of parents of children with autism try dietary intervention," said Dr. Fred Volkmar, Director of the Child Study Center at Yale University.
"The sad reality of it is that with any complementary alternative treatment -- there is no evidence. It's what makes it complimentary alternative treatment," said Volkmar.
Volkmar said his patients try the restrictive diets after hearing anecdotes from other parents, which is not proof enough for scientists and doctors. He also thinks parents are keen to pick up on diets as a form of treatment because a common characteristic in children with autism is finicky eating.
Rebecca Estepp, a mother of a boy with autism and national policy manager for Talk About Curing Autism, said she first started wondering about her son's diet for those very reasons.
"I put my son on this diet nine years ago, and there was no evidence but the evidence of my son's constant diarrhea, constant indigestion," said Estepp. "He also avoided milk. I kept thinking, what two- year-old pushes away the milk cup?"
Estepp said her son's health improved after she put him on a restrictive diet. It didn't cure his autism, but his better health led to better behavior.
"I think a lot of the time these kids are misbehaving because they don't feel well," said Estepp, who said her son and others may be acting out and unable to communicate their pain.
Although studies on the diets are lacking, Estepp said she was "ecstatic" that doctors are making recommendations on how to approach treating stomach problems in children with autism.
"That makes all the difference in the world to someone who cannot speak," said Estepp. "I wished this had happened 10 years ago when my child was diagnosed."
If done well, Volkmar said children can live on the diets and stay relatively healthy. The only problem Volkmar sees with the diets is that "occasionally parents get so crazy with the diet that they lose perspective." He has seen parents so focused on diets that they miss other medical problems or neglect behavioral therapies that have been proven effective in rigorous studies.
"Sometimes you have parents who pursue a treatment that has not been shown to work, to the detriment of treatments that have been shown to work," he said.
But parents who want hard scientific evidence before trying the casein-free, gluten-free diets may have to wait a while.
"For many researchers this would be a lower priority. The problem is there's limited federal dollars, it's an amazing amount of work to get these [treatment] studies done," said Volkmar.
Complicating the problem is the vast spectrum of behaviors and medical issues within autism. Gastrointestinal issues may be more common in some parts of the spectrum but not in others. Doctors say lumping children with autism into one diet study may confuse the results.
"Studying them [patients] in large groups of people who are heterogeneous -- very different from one another -- is not the best way to learn what is going on with these diets," said Dr. Martha Herbert of Massachusetts General Hospital in Boston. "You will wash out any effect in a subgroup by blurring them in with others who have different problems."
Dr. Arthur Beaudet, who contributed to the published statements, said he believes genetic studies may one day lead to better research of gastrointestinal problems in children with autism.
For instance, children with autism symptoms caused by one genetic mutation may be more likely to develop gastrointestinal issues than children who have a different genetic mutation -- or none at all.
Beaudet said current research has already pinpointed subgroups of people with autism who have a specific mutation and distinct behavior, such as the estimated 1 percent of people with autism who have the mutation known as "16p11.2"
"There's a very broad spectrum of autism from very severe handicaps to very mild handicaps… we have to break these down to the smallest extent possible," said Beaudet.