8. Short-Term Decreases in Performance
As discussed above, removing carbs can lead to general tiredness at first. This includes an initial decrease in exercise performance.
It is primarily caused by the reduction in your muscles’ glycogen stores, which provide the main and most efficient fuel source for all forms of high-intensity exercise.
After several weeks, many ketogenic dieters state that their performance returns to normal. In certain types of ultra-endurance sports and events, a ketogenic diet could actually be beneficial.
There are also some further benefits, primarily an increased ability to burn more fat during exercise.
One famous study found that athletes who had switched to a ketogenic diet burned as much as 230% more fat when they exercised, compared to athletes who were not on a ketogenic diet (19).
While it is unlikely that a ketogenic diet can maximize performance for elite athletes, once you become fat-adapted it should be sufficient for general exercise and recreational sports (20).
Bottom Line: Short-term decreases in performance can occur. However, they tend to improve again after the initial adaptation phase is over.