Ketogenic diet therapy (KDT) is an established nonpharmacologic treatment in various types of epilepsy. We aim to evaluate the quality of the systematic reviews and meta-analyses (SRMAs) of KDT for epilepsy and summarize the evidence on their effects. We conducted an overview on MEDLINE, EMBASE, Cochrane Database of Systematic Review, and Web of Science from database inception to 3 September 2020. Two investigators independently performed study selection to include SRMAs, extracted data and assessed the quality of SRMAs with the AMSTAR-2 and PRISMA statement. Twenty-four SRMAs were selected which encompassed a total of 255 original studies. Four reviews assessed the effects of KDT on infant patients; thirteen reviews reported on children and adolescent patients; eight reviews focused on adults or all patients; four assessed cognitive and behavior outcomes; three assessed quality of life; two assessed growth and development outcomes; seventeen reported on adverse effects; seven reported on retention; ten reported on attrition and reasons; and four reported on death outcomes. Overall, positive effects of KDT for epilepsy on seizure frequency reduction, as well as cognition and behavior were observed. In contrast, the effects of KDT on quality of life, growth and development were more controversial. The present overview indicates that KDT is safe. The most prevalent adverse events were GI, weight loss, and metabolic disorders, while the most common reasons for discontinuance were the lack of observed efficacy and dietary intolerance.