Dietary patterns associated with autism spectrum disorder more than specific gut microbiome associations

April is World Autism Awareness Month which raises awareness about these conditions that impact communication, social interaction and behavior affecting about 1 in 160 children worldwide and 1 in 44 in the US.

There is a growing interest in the role diet plays in behavior, yet current studies have yielded inconsistent results directly linking the gut microbiome as the cause of certain behaviors such as anxiety and depression.

 The interest in the potential link between autism spectrum disorders and the gut microbiome has exploded due to the high rates of occurring gastrointestinal symptoms in this patient population as well as the growing interest in the gut-brain axis.

Despite this interest, recent studies have not accurately pinpointed if and how the gut microbiome contributes to autism spectrum disorders (ASD) compared to children who are not diagnosed due to a small sample size and differences in study design.

To fill the knowledge gap about the potential role the gut microbiome plays in ASD, professor Jacob Gratten and colleagues from the University of Queensland analyzed 247 children aged 2-12 years old, which included ASD patients, siblings without a diagnosis and unrelated children without an ASD from the Australian Autism Biobank and the Queensland Twin Adolescent Brain project.

Stool samples were collected for metagenomic analysis and they used the Bristol Stool chart to determine stool consistency. Dietary data from an eating survey was also analyzed. The authors of the study also compared other factors such as age, sex, neurodevelopment traits and sleep habits to see if any cofounding factors were correlated with the gut microbiome.

Surprisingly, in contrast to previous microbiome studies in ASD patients, the authors did not find a direct association between the gut microbiome and ASD with the exception of the species Romboutsia timonensis, which was lower in ASD patients.

Interestingly, they discovered that certain behaviors, such as repetitive and restrictive eating and sensory preferences, correlated with a less diverse diet and microbiome and looser stools. These results are not in agreement with recent studies that advocate for the gut microbiome as a potential therapeutic target to treat ASD.

Additionally, Gratten and his team observed a higher rate of loose stools in these subjects, which means they experienced less colonic absorption of water and a faster transit time, both of which affect gut microbiota diversity.

Key Takeaways

Although the authors could not identify a direct association between the gut microbiome and ASD, they did uncover that ASD patients were much more likely to have a less diverse diet. Restrictive diets could lead to nutrient deficiencies which consequently could affect behavior. 

Despite the weak association discovered between the gut microbiome and ASD that goes against several previous studies, it does highlight the importance of focusing on improving diet diversity and quality in ASD patients to improve their overall health and behavior. 

The authors also hypothesize that perhaps behavior is what influences the gut microbiome, not the other way around. This study also emphasizes that restrictive diets may actually be the driver behind certain ASD behaviors that consequently affect the gut microbiota composition.

Reference: Yap et al., Autism-related dietary preferences mediate autism-gut microbiome associations, Cell (2021), https://doi.org/10.1016/j.cell.2021.10.015