I'm relatively new to calorie restriction. I began by doing the 5:2 split and upgraded to doing a water fast on every Tuesday and Thursday. I'm finding that when I exercise on those days, whether it be cycling or running, I bonk (run out of steam) quickly. Sometimes I run or cycle for several hours at a clip. What should I do? What is the best way to avoid bonking, yet maintaining a CR lifestyle? Best things to eat during endurance exercise sessions (5 hours plus)?