Autism spectrum disorders (ASD) are neurodevelopmental disorders whose symptoms manifest as early as the fetal period and are visible throughout a person’s lifetime. ASDs are characterized by impaired social and communication skills as well as limited, repetitive interests and behaviors. Epidemiological studies show that the incidence of ASD is increasing and early diagnosis is crucial because it allows a faster improvement in a person’s quality of life. Genetic and environmental factors contribute to the development of ASD, but the exact ethology is still unclear. There is a number of hypotheses about the origin of ASD, from metabolic abnormalities, food allergies to changes in the microbiome. Pregnancy is also of great importance, due to metabolic disorders before and during pregnancy, unbalanced diet of mothers before conception and increased frequency of infections during pregnancy. Certain symptoms that occur in all forms of ASD include gastrointestinal disorders, leaky gut syndrome included. The most common food allergies which seem to correlate with ADS include gluten, casein and lactose, which is why many ASD patients are put on restrictive diets. These diets pose a number of nutritional deficiencies risks. On the other hand, supplementation with vitamins and minerals, diet rich in proteins and probiotics are recommended for ASD. Despite large number of studies, currently available evidence do not fully support any of the specific dietary approach. One possible reason is the complexity and variety of symptoms that occur in people with ASD.