BACKGROUND: Use of high-fat diets to support physical performance has grown in popularity over recent years. While this strategy allows for enhanced fat oxidation and reduced reliance on carbohydrate for fuel during exercise, its ability to improve physical performance has not been consistently shown. PURPOSE: Determine effect of high-fat diets (FAT) on physical performance compared to control carbohydrate diets (CHO). METHODS: Meta-analysis was conducted on studies with healthy (BMI < 30) trained or untrained men or women consuming isocaloric FAT (> 50% total energy intake) compared to control CHO diets for > 2 days, followed by a physical performance test. Performance outcomes were grouped as endurance (time to exhaustion, time trial, and VO2max) and power/strength. Data presented as effect size [ES (95% CI)] using Hedges’ g with random effects. Analysis was conducted on crossover and parallel study designs separately. RESULTS: A total of 31 studies (21 crossover, 10 parallel) containing 51 subgroups (31 crossover, 20 parallel) were identified. Overall, FAT had no effect on physical performance in crossover [-0.13 (-0.36, 0.11)] or parallel [-0.18 (-0.53, 0.17)] studies compared to CHO. Stratified by training status, FAT had no effect on trained individuals in crossover [-0.08 (-0.26, 0.09)] or parallel [0.05 (-0.17, 0.26)] studies compared to CHO. In untrained individuals, FAT had a negative effect [-1.14 (-2.01, -0.28), P < 0.05] in parallel studies compared to CHO, and no effect [-0.32 (-1.22, 0.57)] in crossover studies compared to CHO. Stratified by performance outcome, FAT had no effect on endurance performance in crossover [-0.10 (-0.26, 0.09)] or parallel [-0.27 (-0.80, 0.25)] studies compared to CHO. FAT had a negative effect on power/strength [-0.23 (-0.45, 0.00), P < 0.05] in crossover studies compared to CHO. FAT had no effect on power/strength [-0.08 (-0.44, 0.27), P < 0.05] in parallel studies compared to CHO. CONCLUSION: Overall, these data indicate FAT does not have a positive effect on physical performance compared to control CHO. This material is based on the work supported by MRDC; authors’ views not official U.S. Army or DoD policy.