Short-Term Moderately High-Fat Diet Has No Effect on Physical Performance

Purpose: Military personnel and first responders engage in physically demanding activities resulting in high daily energy expenditures, often coupled with inadequate energy intake. Increasing dietary fat for short durations (<6 d) is one strategy to increase energy intake. However, some studies suggest that short-term high-fat diets may impair endurance performance, while other research indicates that longer-term high-fat diets appear to have no effect on performance. Methods: This randomized crossover study aimed to determine the impact of a short-term moderately high-fat diet (MHF; 40% of total kcal) compared with a standard fat diet (SF; 30% of total kcal) on multiple dimensions of physical performance. Twenty healthy adults (22 ± 5 y, body mass: 80.3 ± 12.2 kg, : 47.9 ± 9.0 mL·kg·min −1 ] consumed controlled, weight-maintaining, isocaloric, protein-matched MHF and SF diets for 5 d, separated by ≥7 d. To assess physical performance, participants completed vertical jump, 4-mile time trial, and time to exhaustion (85% ) tests and the six-event Army Combat Fitness Test before and immediately after each intervention. Results: Consistent with the experimental design, the MHF diet resulted in a higher proportional energy intake from fat (41 ± 1% vs 30 ± 3%; P < 0.001) and less from carbohydrate (40 ± 1% vs 52 ± 4%; P < 0.001) versus the SF diet, without differences in energy intake (MHF: 2474 ± 297 vs SF: 2493 ± 303 kcal·d −1 ; P = 0.25). No between-group differences in any performance measure were observed ( P ≥ 0.05). Conclusions: Short-term consumption of a higher-fat diet neither impaired nor meaningfully improved measures of physical performance.