In a recent supplement of the journal Pediatrics is published the report of a consensus panel on the issue of gastrointestinal (GI) disorder in children with autism. This is not a new study and no new evidence is presented – it is a systematic review of the literature by 28 experts from various disciplines. These formal expert reviews are often a helpful way to make sense of a large and complex medical literature on a specific question.

The most significant finding of the panel is that:

The existence of a gastrointestinal disturbance specific to persons with ASDs (eg, “autistic enterocolitis”) has not been established.

In addition they found that there is no evidence for benefit from special diets. About 1 in 5 children with autism are on a special diet designed to improve the symptoms and outcome of autism, usually by removing gluten or casein from the diet, but there is simply no scientific evidence that such diets are helpful.

The alleged link between GI disorder and ASD was started by the now-discredited study by Andrew Wakefield in 1998. He proposed a “leaky gut syndrome” that allowed the measles vaccine to cause an infection which eventually led to the brain damage that causes autism. His research was later refuted and he is now even suspected of fraud. But the idea that GI disorders contribute to ASD was out in the public and took on a life of its own, separate from scientific evidence.

Now, more than 10 years later, the evidence is largely against the notion that there is a GI condition specific to ASD. But the report is also careful to point out that there is insufficient research to rule out such conditions either. This reflects the usual conservative style of such scientific writing. One of their bottom-line recommendations is for more research in this area – not necessarily to explore the possibility that a GI disorder causes autism, but rather what spectrum of GI disorders are seen in children with ASD and do they require any special treatment or diagnostic approach.

For professionals the panel recommends that they approach a child with ASD and GI symptoms as they would any other child – meaning that children with ASD deserve the same diagnostic workup as any other child with similar symptoms. They do not require any special workup, but neither should their GI symptoms be ignored. They further recommend that special intervention may be necessary for the behavioral consequences of GI symptoms when they do occur. When a child with ASD does have a GI disorder, the pain and other symptoms may trigger problem behavior, and therefore special care may need to be taken not only to treat the GI symptoms but to mitigate the negative effect on behavior.

For professionals and for parents the panel concludes that there are no special diets that have been shown to be of benefit in children with ASD, despite anecdotal reports. Further, children on special diets may be at risk for malnutrition, and therefore nutritional status needs to be assessed.

This is likely to be the most controversial aspect of the report in the autism community. Parents who have observed anecdotally that their child’s behavior improves on a special diet are unlikely to be swayed by a scientific analysis. There is insufficient evidence to rule out an effect, but there is also good reason to be skeptical of the anecdotal reports. It is true that parents intimately know their own children, but this familiarity does not protect them from the powerful effects of confirmation bias.

We have been here before – with alleged food allergies, and the whole sugar causes hyperactivity myth. Confirmation bias is the tendency for uncontrolled observations to confirm what is already believed or suspected. It is largely why we need blinded and controlled observation. For example, people tend to observe and remember those incidents that confirm their beliefs, and ignore or dismiss those that would contradict the belief. It is subtle and subconscious, and impossible to filter out completely just by conscious effort.

Also, there is a tendency to look for confirmation. For example, when a child is hyperactive or exhibiting bad behavior the parent may ask – what did they eat recently? They will look for, and potentially find, an offending substance (sugar, gluten, dairy, whatever) and this will confirm their belief that the food causes the behavior. However, if they do not find an offending substance, this is a non-event and it does not register with them and is soon forgotten. Even more subtle is the fact that the parents will not ask the question – what did my child eat recently? – when they are not misbehaving. And so they will not be aware of the fact that the probability they had the alleged offending food is the same, regardless of the child’s behavior.

This is the exact same psychological factor that leads to superstition, to sports myths, and to the common belief in the lunar effect. I have personally witnessed ER staff look up from their busy work and say, “The ER is crazy tonight, is there a full moon?” The answer on that occasional was “no,” and so they quickly forgot the thought. But when the answer is “yes” it is remembered as powerful confirmation of a lunar effect. Meanwhile, controlled observations clearly show that there is no lunar effect – it is all an illusion.

But humans appear to be hard-wired to be powerfully compelled by their own confirming observations, and it is difficult to impossible to convince someone with scientific data that their personal observations were misleading. This effect is exacerbated by the strong emotional attachment of a parent to their child (a connection of which I am personally aware and completely understand) – and the overwhelming feelings of protectiveness.

This is all the more reason for the medical community to give objective information to parents, and this panel report will be extremely useful in making recommendations for today but also pointing the way to future research. But this only helps when there is a baseline respect for science and the institutions of science.