Abstract
BACKGROUND: The ketogenic diet (KD) has gained popularity as an efficient approach to weight loss and body fat loss. Concerns about reducing muscle mass and performance have been rising during weight loss, as muscle mass and functionality are crucial for health. However, the effects of the KD on muscles not only for athletes or trainers but also for adults with less physical exercise are still controversial. METHODS: We conducted a thorough search of databases including Embase, PubMed, Cochrane Library, and Web of Science up to July 19, 2025. Three aspects of muscle assessment were conducted, including muscle mass, power and strength, aerobic metabolic capacity, and endurance. We included randomized and non-randomized controlled studies that compared the KD with other dietary interventions. Studies without control groups were excluded. A random-effects model would be utilized when significant differences in populations and interventions across studies were of concern. The GRADE system was employed to assess evidence quality, while evidence reliability was gauged via sensitivity analysis. RESULTS: A total of 33 studies were analyzed, revealing no significant differences between the KD and other diets in muscle mass (WMD: 0.06, 95%CI: -1.97 to 2.09, p = 0.95), muscle power (countermovement jump: SMD: -0.06, 95%CI: -0.49 to 0.38, p = 0.80) and strength (squat: SMD: -0.19, 95%CI: -0.53 to 0.15, p = 0.27; bench press: SMD: -0.15, 95%CI: -0.49 to 0.18, p = 0.37). However, a significant decrease in fat-free mass (WMD: -0.48, 95%CI: -0.73 to -0.23, p < 0.001) and fat mass (WMD: -1.31, 95%CI: -2.06 to -0.57, p < 0.001) was observed in the KD group compared with the control group. The KD also improved fat oxidation (WMD: 0.13, 95%CI: 0.08 to 0.17, p < 0.001) and reduced respiratory exchange ratio (WMD: -0.07, 95%CI: -0.11 to -0.03, p < 0.001) during an exercise test. The VO(2max) and VO(2max) relative to body weight, treadmill time to exhaustion, and rating of perceived exertion were not significantly affected by KD. CONCLUSIONS: Among adult populations, KD can increase fat oxidation to modify muscle metabolism, while no significant reduction in muscle mass or strength was observed. Additional well-designed randomized controlled trials are warranted to definitively determine the effects of ketogenic diets on muscle parameters.