Experts say the gut microbiome–autism link might have to be reversed. 

The gut microbiome may not drive autism, according to a new Australian study. 

“While it’s a popular idea that the microbiome affects behaviour, our findings flip that causality on its head,” says researcher Chloe Yap, who is completing her medical degree and PhD at The University of Queensland.

Her research team examined genetic material from stool samples of 247 children, including 99 children diagnosed with autism.

“We found that children with an autism diagnosis tended to be pickier eaters, which led them to have a less-diverse microbiome. This in turn was linked to more-watery stools.  So, our data suggests that behaviour and dietary preferences affect the microbiome, rather than the other way around,” Ms Yap said. 

Of more than 600 bacterial species identified in the gut-microbiomes of study participants, only one was associated with a diagnosis of ASD.

“There’s been a lot of hype around the gut microbiome in autism in recent years, driven by reports that autistic children have high rates of gut problems. But that hype has outstripped the evidence,” says the head of Mater Research’s Cognitive Health Genomics Group, Dr Jake Gratten.

He said the experimental use of microbiome-based interventions such as faecal microbiota transplants and probiotics, that some believe may treat or minimise autistic behaviours, should possibly be paused.

“We are already seeing early clinical trials involving faecal microbiota transplants from non-autistic donors to autistic people, despite not actually having evidence that the microbiome drives autism. Our results suggest that these studies are premature,” Dr Gratten said. 

Autism CRC Research Strategy Director, Professor Andrew Whitehouse, said the findings provide clarity to an area that has been shrouded in mystery and controversy.

“Families are desperately seeking new ways to support their child’s development and wellbeing. Sometimes that strong desire can lead them to diet or biological therapies that have no basis in scientific evidence,” Professor Whitehouse said.

“The findings of this study provide clear evidence that we need to help support families at mealtimes, rather than trying fad diets. This is a hugely important finding.”

Autistic person Trudy Bartlett says the research findings provide an important step forward for the autism community.

“I have found that many autistics have gut issues, which I thought may be linked to the fact that many of us - including myself - have restrictive diets so we may not get all the nutrients we should. Wanting to know more about it is like walking through a minefield trying to filter fact from fiction,” she said.

“Having evidence-based research like this study will help members of the autism community to navigate this space and not spend copious amounts of money and time on fads that claim to improve the quality of life for an autistic person.”

The study is accessible here.