Introduction: The ketogenic diet, a restrictive diet, is mainly characterized by high fat content, low or absent carbohydrate content, and low or normal amounts of protein. Objective: It was to present the important role of the ketogenic diet in the treatment of obesity and other chronic diseases. Methods: The PRISMA Platform systematic review rules were followed. The research was carried out from September to October 2023 in the Scopus, PubMed, Science Direct, Scielo, and Google Scholar databases. The quality of the studies was based on the GRADE instrument and the risk of bias was analyzed according to the Cochrane instrument. Results and Conclusion: A total of 111 articles were found, and 44 articles were evaluated, and 22 were included in this systematic review. Considering the Cochrane tool for risk of bias, the overall assessment resulted in 19 studies with a high risk of bias and 32 studies that did not meet GRADE. Most studies showed homogeneity in their results, with X2=65.7%>50%. It was concluded that the therapeutic use of the ketogenic diet is relevant in the treatment of obesity and metabolic syndrome. Furthermore, this work also showed the benefits of the metabolism of ketone bodies in the adjuvant treatment of cancer, diabetes, and obesity, thus contributing to updating knowledge about the use of the ketogenic diet in the therapy of diseases of great clinical and epidemiological importance. When it comes to obese and diabetic people, it is important to highlight that due to the lower consumption of fiber, and an increased consumption of proteins (mainly of animal origin) and fat, the risk of heart disease, colon cancer, and intestinal constipation increases.