Pre- and probiotics for gastrointestinal and behavioral symptoms in autism spectrum disorder: a systematic review.

OBJECTIVES: Many studies have explored whether targeting gut microbiota (GM) could improve health outcomes in neurodevelopmental conditions. In this way, this systematic review examined whether pre- and/or probiotic interventions could modulate GM and reduce gastrointestinal (GI) and behavioral symptoms in individuals with autism spectrum disorder (ASD). METHODS: A comprehensive search was conducted in PubMed, Scopus, and Embase. Eligible studies included participants with ASD diagnosis who received prebiotic and/or probiotic treatment, with outcomes assessing GM- and ASD-related symptoms. From 8795 records identified, 15 studies met the inclusion criteria, totaling 1015 participants. RESULTS: Most probiotic formulations used Bifidobacterium and Lactobacillus strains, and prebiotics, such as galactooligosaccharides. Reported effects included microbiota changes and improvements in GI symptoms, such as reduced abdominal pain. Behavioral benefits were described in some studies, but less consistently. DISCUSSION: Microbiota-targeted interventions were considered safe and, in most cases, effective in alleviating GI symptoms. However, behavioral improvements were variable and possibly influenced by strain specificity, treatment duration, and concurrent dietary factors. Despite the potential as an adjunctive strategy for managing GI comorbidities, their role in addressing core ASD symptoms is unclear, and current evidence is more consistent for GI symptoms than for behavior. Some reported benefits may reflect combined interventions rather than probiotics or prebiotics specifically. Additionally, most participants were children, with limited representation of older individuals. Larger, long-term trials with rigorous designs are needed to clarify clinical relevance, uncover underlying mechanisms, and identify which patients are most likely to benefit from these interventions.