Systematic review of dietary interventions in autism spectrum disorder

Background: Autism spectrum disorders (ASD) are an ever-increasing group of neurobiological developmental disorders, affecting every aspect of the affected individual’s life. As a heterogeneous disorder of which the aetiology is unknown, many desperate attempts have been made to find a cure for this group of disorders. Methods of treatment currently suggested for the treatment of ASD include educational interventions, medical treatment, complementary and alternative methods of treatment, and dietary interventions. The efficacy of dietary interventions currently suggested in the lay media for the treatment of the signs and symptoms related to ASD is largely unknown. Objective: The aim of the study was to critically appraise dietary interventions suggested in peer-reviewed literature for the treatment of signs and symptoms related to ASD in children aged birth to 18 years. Methods: A systematic literature strategy was undertaken. The initial literature search yielded a possible 62 studies of which 33 studies were excluded for not adhering to the inclusion and exclusion criteria. To be included, studies had to evaluate a dietary intervention in children with ASD aged birth to 18 years, and be published in English between January 1990 and July 2012. The 29 included articles reported on gluten-free, casein-free (GFCF) diet; specific carbohydrate diet; elimination diet; ketogenic diet; detoxification diet and therapies; supplementation of digestive enzymes; probiotics; polyunsaturated fatty acids; inositol; vitamin and minerals; yeast-free diet and implementation of two or more methods of treatment simultaneously. Results: No firm conclusion about the efficacy of dietary interventions in the treatment of ASD could be made. The review was limited by the small number of scientific articles published on this topic, and the heterogeneous nature of the studies. A meta-analysis could thus not be conducted. Of the dietary interventions evaluated, the GFCF diet was most likely to yield a positive outcome. This could not be confirmed due to different methodological approaches and reporting used by the different researchers. The following factors did, however, impact on the outcome of the dietary interventions and should be taken into account when implementing a dietary intervention to treat ASD: the length of intervention period, the degree of adherence to the dietary modification, age of individuals, sign and symptoms perceived prior to the intervention, severity of the ASD, and the combination of the treatment given. Conclusion: Evidence-based research is yet insufficient to make any firm conclusion about the efficacy of the dietary interventions currently suggested for the treatment of ASD. Further research based upon methodologically sound research methods is thus recommended.