The much-hyped link between autism and gut dysbiosis has cause and effect the wrong way round.
Faecal microbiota transplantation for people with autism is very unlikely to achieve results, despite the “hype”, Australian researchers now say.
It’s more likely that the high rates of co-occurring autism and gastrointestinal symptoms are driven by autism-related dietary preferences, rather than a brain-gut-microbiome interaction.
This new insight comes as interest in faecal microbial transplants for children with autism increases, with one 2019 study reporting an improvement to autism-related symptoms at the conclusion of an open-label microbiota transfer trial.
However, University of Queensland researcher Chloe Yap said, in an analysis of studies on the autism gut association, that her team had found an imbalance of primary and secondary research on the link.
While they found 56 review articles looking at autism and the microbiome, there were only 26 primary research studies.
“It was a reflection of the degree of ‘hype’ that the field has come to over time,” she told The Medical Republic.
“That was a significant motivator for us to do our own analysis, contribute to the primary evidence base and hopefully actually give answers rather than speculation.”
To investigate the relationship, University of Queensland and Mater Hospital researchers did a stool metagenomics study of 247 children from the Australian Autism Biobank and the Queensland Twin Adolescent Brain project, both of which collect extensive phenotype data.
After controlling for a number of confounding factors including sex, age and diet, researchers found there was negligible evidence for a direct association between stool microbiome and an autism diagnosis – or any other neurodevelopmental traits, for that matter.
“Instead, we found evidence linking behaviours associated with the autism spectrum (e.g., repetitive-restricted behaviours or interests, sensory preferences, and social affect) to reduced dietary diversity, which, in turn, was associated with reduced microbiome diversity and looser stool consistency,” the researchers wrote in Cell.
People with autism had a significantly less-diverse diet and lower dietary quality in comparison to their peers.
Essentially, the authors believe, autism-related sensory preferences and restricted interests lead to a less-diverse, lower quality diet which affects gut ecology, leading to looser stools and gastrointestinal discomfort.
“At first, it was sort of puzzling why this hadn’t been put together before, in a sense, because it is so [simple],” Ms Yap said.
“I mean, there was one Twitter comment I saw that was like, ‘this should be published in the International Journal of Duh.’
“But it also comes back to that element of hype and the interest that kind of comes into this [area] as well.”
Ultimately, Ms Yap hoped that the study findings can help provide clarity for GPs treating people with autism and their families who may have seen or bought into the hype.
“I think the second major implication is to shift the spotlight away from the microbiome and more to the importance of a healthy, balanced diet for kids on the autism spectrum and the need to support children and families at mealtimes,” she said.
This could include a multidisciplinary team approach involving dieticians, speech pathologists and psychologists to address the autism-associated traits and preferences that drive dietary preferences.