The effect of a six-week ketogenic diet on VOp2smax, Wingate sprints, and prolonged exercise performance
The purpose of this study was to determine the effect of a 6-week ketogenic diet on maximal oxygen consumption (VO2max), high-intensity Wingate sprints, and work output during a 45-minute cycling bout. Twenty subjects were placed into either an intervention group (N=12) or a control group (N=8). Subjects in the dietary intervention group ingested a diet consisting of 61± 4% fat, 8± 3% carbohydrate, and 30± 5% protein while subjects in the control group were instructed to continue following their normal moderate carbohydrate diet. All subjects were instructed to maintain their current training status. On the first day subjects performed a VO2max test on an electronically braked cycle ergometer. On the second day subjects performed two 30-second Wingate sprints followed by a 30-minute rest. Following this subjects performed a 45-minute timed ride on a cycle ergometer set on isokinetic mode. Absolute VO2max decreased significantly (P<_ 0.05) in the ketogenic group while relative VO2max was unchanged. Rate of perceived exertion increased significantly at 9 and 11 minutes during the VO2max test. Absolute peak and mean power output during the first Wingate sprint was significantly less after the ketogenic diet compared with week 0. When analyzed relative to body weight, however, only peak power output was significantly decreased. Power output during the second sprint remained unchanged. Fat oxidation increased but work output decreased during the 45-minute cycling bout in the ketogenic group. The results of the present study suggest that a 6-week ketogenic diet results in metabolic adaptations that increase fat oxidation. However, the overall decreased performance during a VO2max test, 30-second Wingate sprints, and a 45-minute endurance test indicate that some aspect of the diet has an adverse effect on exercise performance.