This is one theory among many others put forward to explain the enigma that is autism.

Some children with an Autism Spectrum Disorder (ASD) appear susceptible to gastrointestinal (GI) conditions. Indeed, Autism Speaks, the US based organisation, funded the development of evidence-based guidelines for physicians to use to screen, assess, and treat GI conditions in children with autism, recognising that their treatment can improve the quality of life for these children and their families.

However, this research is in the early stages, with the findings to date providing no evidence that gut bacteria and their by-products cause autism, even a subgroup of them, or that treating the gut can alleviate the specific symptoms of autism.

Like the discredited MMR vaccine theory, the gut theory targets those cases of ‘regressive’ autism, where young children develop symptoms after a period of seemingly typical development. Regression most commonly occurs between 15 to 20 months of age, and these children tend to have more severe symptoms. Whether these are the children who are most vulnerable to GI problems remains to be determined.

Caution needs to be exercised in implementing treatments based on a theory with an insufficient evidence base. Unproven treatments can incur high costs to vulnerable families, often at the expense of securing effective behaviourally based intervention for which there is a solid evidence base.