Do Ketogenic Diets Produce Greater Weight Loss than Higher-Carbohydrate Diets Under Comparable Prescribed Energy Conditions? A Systematic Review and Meta-Analysis of Randomized Controlled Trials

Background/Objectives: Whether ketogenic diets provide greater weight-loss benefits than higher-carbohydrate diets when prescribed energy intake or targeted energy deficit are comparable remains uncertain. This systematic review and meta-analysis evaluated their effects on body weight change in adults with overweight or obesity. Methods: Following PRISMA 2020, PubMed, Scopus, and Web of Science were searched for randomized controlled trials comparing ketogenic diets with higher-carbohydrate diets under matched energy prescriptions. Ketogenic diets were defined as providing ≤50 g carbohydrate/day or ≤10% of total energy from carbohydrate. A random-effects meta-analysis used restricted maximum likelihood estimation and the Hartung–Knapp adjustment. Risk of bias and certainty of evidence were assessed using RoB 2 and GRADE, respectively. Results: Eight reports representing seven studies were included in the systematic review; six studies comprising 259 participants contributed to the meta-analysis. Ketogenic diets were associated with slightly greater weight loss than higher-carbohydrate diets (MD = −1.49 kg; 95% CI: −2.41 to −0.58; p = 0.008; I2 = 0%). Estimates remained similar after alternative imputations of change-score standard deviations, exclusion of the trial at high risk of bias, and leave-one-out analyses. In three trials meeting the prescribed protein-matching criterion, the effect remained directionally consistent but was imprecise and compatible with no difference. Certainty of evidence was low because of risk of bias and imprecision. Conclusions: Under comparable prescribed energy conditions, ketogenic diets may produce a small additional reduction in body weight. However, predominantly short-term evidence, uncertainty regarding achieved energy and protein intakes, the absence of a synthesis of body composition, and low certainty of evidence limit confidence in the magnitude, durability, and clinical significance of this advantage.