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

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.

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.

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).

Short-term consumption of a higher-fat diet neither impaired nor meaningfully improved measures of physical performance.