"One of the problems with many athletes is that they simply do not eat enough to meet the energy needs of their training activities. A recent review by researchers from the University at Buffalo, New York, highlighted several studies in which subjects with reduced energy intakes (500 to 800 kcal/day below estimated expenditure) showed reduced endurance exercise times. Increasing the subjects' caloric intake to match expenditure by increasing carbohydrates significantly increased their time to exhaustion by approximately 20% at exercise intensities of 70% and 80% of Vo2max. However, increasing the total caloric intake to meet expenditure by using fat brought about further significant increases in endurance time - an extra 40% over and above that produced by consuming extra carbohydrates! In these studies, the percentage of fat was raised from 15% to between 30% and 42% of total calories, while carbohydrates were limited to 35-40% of calories.(1)


Yes, so they went to a diet that included 30 and 42% fat and did better than when they weren't given enough calories to eat. WOW! And then they exercised longer and slower on the diet with 30 and 42% fat. Great! Sounds like the way to go for your 4+ hour bike rides.