Microbiome differences in autism reflect dietary preferences, says study

Earlier studies suggest that autism spectrum disorder (ASD) might be partly due to differences in the gut microbiota composition. This is based on the observation that specific types of microorganisms are much common in individuals with autism.

This illustration depicts new research suggesting that the diversity in bacterial species found in the guts of children with autism may be due to their restricted dietary preferences associated with autism, rather than the cause of their symptoms. Image Credit: Chloe Yap.

However, a recent study indicates that the association might work the other way around. The species diversity seen in the guts of autistic children might be due to their restricted dietary preferences linked to autism, rather than the cause of their symptoms. The study was published on November 11^th, 2021, in the Cell journal.

There’s a lot of interest surrounding the role of the gut microbiome in autism, but not a lot of hard evidence. Our study, which is the largest to date, was designed to overcome some of the limitations of prior work.”

Jacob Gratten, Study Senior Author, Mater Research

The next-generation sequencing of the microbial species in the gut over the past years has examined the microbiome as more automated and time-saving. Numerous research works analyzed the association between specific species of microbes in the gut and mental health.

The gut-brain axis is not only associated with ASD but also with depression, anxiety, and schizophrenia. The probability of targeting the microbiota is an emerging field of research for novel treatments.

In the recent research, the scientists examined stool samples from a total of 247 children between the ages of 2 and 17. The samples were gathered from 99 children diagnosed with ASD, 51 paired undiagnosed siblings, and 97 unrelated, undiagnosed children. The children included in the research were from the Australian Autism Biobank and Queensland Twin Adolescent Brain Project.

The researchers examined the samples by metagenomic sequencing—analyzing the whole genome of microbial species rather than small genetic barcodes (as with 16S analysis).

Metagenomic sequencing offers gene-level information instead of species-level information. It also offers a more precise representation of microbiome composition when compared to 16S analysis—a method employed in numerous earlier studies linking the microbiome to autism.

We also carefully accounted for diet in all our analyses, along with age and sex. The microbiome is strongly affected by the environment, which is why we designed our study with two comparison groups.”

Chloe Yap, Study First Author, University of Queensland

Chloe Yap is an MD–PhD Student who works with Gratten.

Depending on their examinations, the scientists discovered limited evidence for a direct link between autism and the microbiome. But they identified a highly crucial link between autism and diet. They also identified that an autism diagnosis was linked with a less-diverse diet and poorer dietary quality.

Additionally, the psychometric measures of the degree of autistic traits (including social communication difficulties, restricted interests, and sensory sensitivity) and polygenic scores (representing a genetic proxy) for ASD and impulsive/compulsive/repetitive behaviors were also linked to a less diverse diet.

Yap adds, “Taken together, the data support a strikingly simple and intuitive model, whereby autism-related traits promote restricted dietary preferences. This, in turn, leads to lower microbiome diversity and more diarrhea-like stool.”

The scientists recognize numerous limitations to the present research. One limitation is that the design of the research cannot rule out microbiome contributions before diagnosis, or the possibility that diet-related alterations in the microbiome have a feedback impact on behavior.

Another limitation is that the researchers can account for the possible impact of antibiotics on the microbiome by excluding those intaking medications at the time of stool collection. Eventually, no comparable datasets are available at present to confirm the observations.

We hope that our findings encourage others in the autism research community to routinely collect metadata in ‘omics’ studies to account for important (but often underappreciated) potential confounders such as diet.”

Jacob Gratten, Study Senior Author, Mater Research, University of Queensland

Gratten further states, “Our results also put the spotlight on nutrition for children diagnosed with autism, which is a clinically important (but underrecognized) contributor to overall health and wellbeing.”

The investigators intend to create new data in bigger samples to replicate their observations.