Originally Posted by Carbonfiberboy

For the OP, riding fasted depletes you. Simple as that. It's all take-away and no put-back. A riding buddy of mine spent some time in India, where like much of the population, he picked up the habit of fasting one day a week. When he came back here and started riding again, he too was puzzled about his low energy for the 2 days following his fast. That meant he couldn't train as hard as he was used to doing and was gradually getting weaker. I got him to quit the fasting and his energy and training came right back no problem.

I'm Jewish and fasting on Yom Kippur, even though it's only from the end of one dinner to the start of the next, is a significant burden which has to be made up for nutritionally. And I definitely don't exercise on YK!