Ten untrained young men ingested a carbohydrate-rich diet (65 energy percent (E%) carbohydrate, T-CHO) and ten similar subjects a fat-rich diet (62 E% fat, T-FAT) while
endurance training was performed 3-4 times a week for 7 weeks. Time to exhaustion at 81 % of pre-training maximal oxygen uptake increased significantly
from a mean of 35 min to 102 and 65 min in T-CHO and T-FAT, respectively, after 7 weeks... It is concluded that ingesting a fat-rich diet during an endurance training programme is detrimental to improvement in endurance.
This is not due to a simple lack of carbohydrate fuel, but rather to suboptimal adaptations that are not remedied by short-term increased carbohydrate availability.