Dysbiosis of the gut microbiota and autism: the role of diet unveiled
A certain theory is gaining momentum, seemingly supported by a number of studies, that an imbalance in the gut microbiota is an important, perhaps even causal, factor of autistic spectrum disorders. Could the microbiota therefore be a target for autism treatment? However, this dysbiosis is not a cause but a consequence of dietary behaviors linked to autism, suggest the authors of a vast metagenomics study published in Cell.
About this article
For several years, the scientific community has shown a keen interest in the possibility of a link between gut microbiota and autistic spectrum disorders. There is clearly an increasing volume of evidence of associations between the gut microbiota and certain neuropsychiatric conditions. Moreover, mice studies appear to have shown that fecal transplantation from autistic patients triggers “autistic behaviors.” Finally, people with autism commonly suffer from gastrointestinal disorders. Spurred on by this array of evidence, several teams have sought to highlight the major role, perhaps even a causal one, that intestinal dysbiosis might play in autism. This would allow us to better understand, diagnose, and even treat autistic spectrum disorders by targeting the microbiota.
Dysbiosis and autism: an exaggerated link?
However, by looking at all the studies and meta-analyses already conducted on this topic, an Australian research team believes that this conclusion is somewhat premature. With differing methods, often based on small population sizes, subject to certain bias and rarely accounting for confounding factors such as diet and age, and inconsistent in their microbial analysis results... these studies do not, according to this team, make a convincing argument.
The researchers therefore conducted a metagenomics study of the intestinal microbiota in 247 Australian children (99 diagnosed with autism and 148 not). Their analysis included several other factors known to alter the gut microbiota such as dietary, clinical, genetic, psychometric, and demographic elements. They found that the composition of the gut microbiota of these children showed only negligible differences between the autism and non-autism groups. Only an abundance of the species Romboutsia timonensis appears to be linked to autistic spectrum disorders. In addition, they were unable to reproduce the results of studies claiming to have established a link between certain microbiota species (e.g., Prevotella and Bifidobacterium) and autism.
Lack of microbiota diversity associated with a lack of variation in the diet
On the other hand, the study did find changes in the composition of the gut microbiota of autistic children that correlated with diet, stool consistency, and age. Certain autistic traits, such as a narrower range of interests, repetitive behaviors, and clear sensory preferences, could affect their diet. According to the research team, autism leads to a diet that is less varied, and therefore of poorer quality. This contributes to a reduced diversity of the intestinal microbiota, which in turn results in softer stools indicative of digestive problems.
Widely reported in the media, this article goes against the tide of theories about a link between the gut microbiota and autism. However, the authors believe that dietary measures could help rebalance gut microbiota in autistic children and thus relieve their gastrointestinal disorders while improving their general health.