Exploratory Dietary Approaches for Drug-Resistant Epilepsy Beyond Standard Ketogenic Diet and Fish Oil: A Systematic Review of Preliminary Clinical Evidence

Background: Standard ketogenic diets (KD) and fish oil have established efficacy for drug-resistant epilepsy (DRE), but adherence and variability remain challenging. Objective: The objective of this study is to provide the first systematic evaluation of clinical evidence for emerging dietary interventions for epilepsy—specifically those other than standard KD and fish oil—and to rigorously evaluate their effectiveness and certainty of evidence to address the current gap in dietary management literature. Unlike prior reviews focused on standard KD or carbohydrate-modified versions, this study is the first to synthesize evidence for “non-standard” interventions—including olive oil-based KDs, probiotics, and restrictive gluten/glutamate-free diets—which are typically excluded from traditional dietary meta-analyses. Methods: Following PRISMA 2020 guidelines, we searched PubMed, Web of Science, Cochrane, and Google Scholar up to March 2025. Randomized Controlled Trials (RCTs) and Non-Randomized Studies of Interventions (NRSIs) were included, with quality assessed using RoB 2 and ROBINS-I tools. Results: Eight studies (total n = 675) were identified, comprising 2 RCTs and 6 NRSIs. These included olive oil-based KDs (n = 1), probiotic/synbiotic supplementation (n = 2), medium-chain triglyceride (MCT) additions (n = 2), and gluten-free (n = 1) or glutamate-free (n = 1) diets. Evidence quality is generally low, with 75% of studies at high risk of bias. Preliminary responder rates reached 83.1% in uncontrolled olive oil-based KD studies, whereas the only RCT evaluating a low-glutamate diet showed no significant seizure reduction (p = 0.57). Conclusion: Evidence for emerging dietary interventions beyond standard KD is nascent and of low certainty. Interpretation: While preliminary signals exist for olive oil-based KDs and probiotics, current data are insufficient for clinical recommendation; this review identifies these as promising exploratory targets requiring validation through rigorous, blinded RCTs.