An opinion piece refutes studies linking gut microbiota and autism

This opinion piece critically analyzes the evidence suggesting a causal relationship between the gut microbiome and autism. The authors argue that this hypothesis lacks a solid foundation, as existing studies have conceptual, methodological, and/or statistical limitations. In particular, they show that specific differences in the microbiome of autistic individuals are inconsistent, small in magnitude, and may reflect consequences of the disorder (e.g., differences in diet or gastrointestinal comorbidities) rather than causes. Many of the problems reflected in this field are common to microbiome studies: low numbers in observational studies, lack of appropriate animal models, establishment of correlations does not imply cause and effect, etc.

I partly share the authors' view on the difficulties of microbiome studies in establishing causal relationships rather than simply correlations, and that in this field the press and industry often exaggerate these results, mistakenly presenting proven correlations as evidence of causality. Such hasty interpretations can be exploited by the nutraceutical or probiotic industry to sell products with unproven efficacy, which can raise false hopes. Today, there is strong evidence of correlations between intestinal alterations and autism, but evidence of causality remains hypothetical and difficult to prove due to the limited size of studies, the large number of uncontrolled factors, and the lack of suitable animal models. Given that autism has high heritability and a complex genetic basis, changes in the microbiome could be more of a consequence than a cause, or be a factor that promotes development when a genetic predisposition exists. Even so, it is essential to continue rigorously investigating possible causal links, while always being cautious in communicating the results so as not to raise false hopes.