Originally Posted by
livedarklions
You're going to have to be a lot more specific. What do you mean by fasting? Intermittent fasting? Extended fasting? How long? Obviously, if you go without intake of calories, you will lose weight, but there's a reason anorexia is considered an eating disorder, you can do yourself great harm.
If you're talking about intermittent fasting, which is basically just confining your eating to certain times of the day, I know people who swear by it, and I doubt you can do yourself any harm. If you're talking about not eating for several days at a time, please don't try this. More likely, you'll lose a lot of muscle tissue, and if you carry it to an extreme, one of those muscles is the heart.
Using "fasted" rather than "fasting," I understood the OP to be talking about fasted rides, which are essentially getting up and going for a longish ride at moderate pace in a fasted state. I do these often, especially in the winter and early spring. Get up, drink a mug of black coffee, and ride at tempo or less for 90-120 minutes. Then eat. You are training yourself to become more efficient at using fat rather than glycogen for fuel.
That's a different thing than going for days without eating.