Effect of ketogenic diets on lipid metabolism in adults: protocol for a systematic review

Introduction The ketogenic diet is a very low carbohydrate diet known for its ability to reduce weight and counteract hyperglycaemia. However, ketogenic diets recommend an increased intake of fats, raising concerns about cardiometabolic risk in adults. Due to the higher intake of fats in the ketogenic diet, there is significant variability in outcomes of lipid metabolism in the population. Interventions have reported improvements in lipid profile while other studies did not find changes, and there are reports of increased low density lipoprotein (LDL) and triglyceride values. Hence, this is a protocol for a systematic review of the published literature and a summary of the effect of ketogenic diets on lipid metabolism in adults. Methods and analysis Five databases (PubMed, Embase, Scopus, Cochrane Library and Web of Science) will be searched for studies on ketogenic diets in adult populations. Studies will be included if they report results from ketogenic diet interventions among adults. Exclusion is populations with diagnosed neurological disorders. Two reviewers will independently screen retrieved citations, extract data and appraise the risk of bias. Quantitative estimates (eg, standardised mean difference) measuring the change in the total cholesterol, LDL and triglyceride concentration will be pooled using random effects meta-analysis to produce one summarised weighted estimate. Sources of heterogeneity will be explored using subgroup analysis. This protocol follows the Preferred Reporting Items for Systematic Review and Meta-Analysis for Protocols (PRISMA), and the final review will be reported following the PRISMA 2020 guidelines. Ethics and dissemination The present protocol and the systematic review to be carried out do not require ethics clearance. The data source will be published studies. This review will provide estimates to inform the public about the effect of ketogenic diets on lipid metabolism and the possible peril of increasing cardiometabolic risk. The results will be published in a peer-reviewed journal.