CONTEXT:Dietary interventions such as restrictive diets or supplements are common treatments for young people with autism spectrum disorder (ASD). Evidence for the efficacy of these interventions is still controversial. OBJECTIVE:To assess the efficacy of specific dietary interventions on symptoms, functions, and clinical domains in subjects with ASD by using a meta-analytic approach. DATA SOURCES:Ovid Medline, PsycINFO, Embase databases. STUDY SELECTION:We selected placebo-controlled, double-blind, randomized clinical trials assessing the efficacy of dietary interventions in ASD published from database inception through September 2017. DATA EXTRACTION:Outcome variables were subsumed under 4 clinical domains and 17 symptoms and/or functions groups. Hedges' adjusted g values were used as estimates of the effect size of each dietary intervention relative to placebo. RESULTS:In this meta-analysis, we examined 27 double-blind, randomized clinical trials, including 1028 patients with ASD: 542 in the intervention arms and 486 in the placebo arms. Participant-weighted average age was 7.1 years. Participant-weighted average intervention duration was 10.6 weeks. Dietary supplementation (including omega-3, vitamin supplementation, and/or other supplementation), omega-3 supplementation, and vitamin supplementation were more efficacious than the placebo at improving several symptoms, functions, and clinical domains. Effect sizes were small (mean Hedges' g for significant analyses was 0.31), with low statistical heterogeneity and low risk of publication bias. LIMITATIONS:Methodologic heterogeneity among the studies in terms of the intervention, clinical measures and outcomes, and sample characteristics. CONCLUSIONS:This meta-analysis does not support nonspecific dietary interventions as treatment of ASD but suggests a potential role for some specific dietary interventions in the management of some symptoms, functions, and clinical domains in patients with ASD.