Microbiota-based therapies as novel targets for autism spectrum disorder: A systematic review and meta-analysis

Autism Spectrum Disorder (ASD) is a complex neurodevelopmental condition characterized by persistent deficits in social interaction and communication. Emerging evidence suggests that alterations in the gut-brain axis play a key role in the pathophysiology of ASD, and that microbiota-targeted interventions may offer therapeutic benefits. However, no clear consensus has been reached regarding the effectiveness of these strategies in ameliorating behavioral characteristics. This systematic review and meta-analysis (PROSPERO registration ID: CRD42023494067) aimed to evaluate the impact of microbiota-based interventions-including synbiotics, prebiotics, single-strain probiotics, probiotic blends, and fecal microbiota transplantation (FMT)-on behavioral outcomes in individuals with ASD, with particular emphasis on social functioning.

Of the 373 records initially identified, 20 studies met the inclusion criteria, comprising 16 randomized controlled trials and 4 open-label studies. The overall effect size indicated a statistically significant improvement in ASD-related behavioral symptoms following microbiota manipulation (Hedges' g = 0.47; 95 % CI: 0.30-0.64; p < 0.001; I² = 33.01 %), representing a small but clinically relevant effect. Heterogeneity was classified as moderate. Among the interventions, FMT and probiotic blends yielded the most substantial effects. All major limitations of the current studies were thoroughly addressed and discussed to guide future experimental designs. Additionally, we examined preclinical evidence supporting the involvement of neural, immune, and metabolic pathways in mediating the observed behavioral improvements.

Our findings support the potential of microbiota-based therapies as a promising and well-tolerated strategy for improving behavioral symptoms in individuals with ASD. FMT and multi-strain probiotic formulations appear particularly effective. Nevertheless, further high-quality randomized controlled trials-especially involving FMT-are urgently needed to validate these results and guide clinical implementation. Thus, these findings provide a critical foundation for future investigations seeking to refine microbiota-based interventions and uncover the underlying mechanisms through which they influence ASD-related behaviors.