Conceptual and methodological flaws undermine claims of a link between the gut microbiome and autism.

The idea that the gut microbiome causally contributes to autism has gained currency in the scientific literature and popular press. Support for this hypothesis comes from three lines of evidence: human observational studies, preclinical experiments in mice, and human clinical trials. We critically assessed this literature and found that it is beset by conceptual and methodological flaws and limitations that undermine claims that the gut microbiome is causally involved in the etiology or pathophysiology of autism.