Updated project metadata. Rationale: Sepsis patients suffer from severe metabolic and immunologic dysfunction that may be amplified by standard carbohydrate-based nutritional regimes. We therefore hypothesize that a ketogenic diet improves sepsis treatment. Objectives: We investigated the safety and feasibility of a ketogenic diet in sepsis patients. Methods: We conducted a monocentric open-labeled randomized controlled trial (DRKS00017710) enrolling adult sepsis patients randomly assigned to either ketogenic or standard high-carbohydrate diet for 14 days with follow-up until day 30. The primary outcome measure was β-hydroxybutyrate serum concentration on day 14. Secondary outcomes included safety, clinical and immunological changes. Measurements and Main Results: 40 critically ill septic patients were assigned to the study groups. Increase in β-hydroxybutyrate concentrations from baseline to day 14 was markedly greater under ketogenic diet (1.2 ±0.9) compared to controls (-0.3 ±0.4); estimated mean difference 1.4 (95%-CI 1.0-1.8; p<0.0001). During ketogenic diet, no patient required insulin treatment beyond day 4, whereas 35% to 60% of control patients did (p=0.0095). Metabolic side effects were not observed under ketogenic diet. Ventilation-free (IRR 1.7; 95%-CI: 1.5 to 2.1; p<0.0001), vasopressor-free (IRR 1.7; 95%-CI: 1.5 to 2.0; p<0.0001), dialysis-free (IRR 1.5; 95%-CI: 1.3 to 1.8; p<0.0001), and ICU-free days (IRR 1.7; 95%-CI: 1.4 to 2.1; p<0.0001) significantly increased in patients under ketogenic diet. There was no difference in 30-day mortality. Analyses indicated favorable changes towards immune homeostasis. Conclusions: Ketogenic diet is a feasible and safe nutritional regimen in septic patients promoting recovery from sepsis-related organ dysfunction and could become a new tool in modern treatment concepts.