In short: yes, if you are looking for performance.
Recently, the low-to-zero-carb diets have increased in popularity, mainly because of their fat-burning effect due to a process called ketosis, in which the body readily burns fat to provide energy.
So, is this kind of diet compatible with competitive endurance training? A recent study in Australia (1) answers this question with a definite NO.
The study examined two groups of elite race walkers, one on a high carbohydrate diet, one on a low-to-zero carb, high fat diet. Although the rate of fat burning in the low carb group was higher, they were actually less efficient in using their energy, needing more oxygen to provide the necessary energy.
This hindered their performance significantly.
The takeaway from this study is that if you are training for performance, you need carbohydrates. Low-carb diets have their place in losing fat, but are not suitable for high-performance training.
Provide adequate carbohydrates in your diet, and use the proper carbohydrate supplements before, during and after training or competing.
(1) Low carbohydrate, high fat diet impairs exercise economy and negates the performance benefit from intensified training in elite race walkers Louise M. Burke1,2, Megan L. Ross1,2, Laura A. Garvican-Lewis1,2, Marijke Welvaert3,4, Ida A. Heikura1,2, Sara G. Forbes1, Joanne G. Mirtschin1, Louise E. Cato1, Nicki Strobel5, Avish P. Sharma6 and John A. Hawley2,7