Last Performance Tip highlighted a multi-study analysis on the ketogenic diet and exercise performance. The overall conclusion was the ketogenic diet did not improve endurance performance. The problem with a multi-study is that the individual studies lacked protocol uniformity and subject selection. For that reason, these types of analysis are always opened to criticism.
That's why a recent well designed study by a respected exercise scientist, should be of great interest to ketogenic diet aficionados. The study, conducted with elite endurance athletes, involved two groups. One group consumed a high fat low carb diet; the second consumed a conventional high carb diet. Both groups completed a 10K run under race conditions. Compared to the high carb group, the high fat low carb subjects increased fat metabolism as expected but also experienced an 8% decrease in endurance performance. This decrease in endurance performance was similar to that seen in other studies involving the ketogenic diet and may result from a decrease in oxygen utilization by working muscles.
After a two-week interval, the subjects on the ketogenic diet were given a high carb diet 24 hours before a second 10K race. Again, compared to the high carb group there was a decrease in exercise performance which suggests that the performance effects of a ketogenic diet cannot be easily reversed by high carb consumption immediately prior to a race.
Although there may be other reasons that people choose to go on a ketogenic diet this study as well as others shows, at least in elite runners, that it decreases exercise performance.