Eating on the fly seems to keep Grands Tours riders alive and healthy ,... and on long rides I do it myself. Your body can absorb nutrients quite well while active—in fact, your body is always active to one degree or another.

There might be difficulties if one tries to eat three cheeseburgers ... the stomach will take extra blood the muscles and lungs might want. However, small quantities a bite at a time works.

I forget how much the body can absorb, something like a couple hundred calories per hour max anyway ... so eating energy bars and such every 15 or 30 minutes is just to keep metabolism constant—so there is no time when the body isn’t processing food into fuel, while the body is burning fuel at several hundred Calories per hour.

If a rider cannot manage breathing, eating, and drinking .... hmmmmm.

I would hope it would be clear that if one was riding so hard one could barely breathe, one would not be able to stop breathing and eat or drink very well. Sometimes when I need to drink and breathe, I take a mouthful of water, breathe hard through my nose (post-drink cleanup required) and swallow small sips until my mouth is empty.

Taking individual small sips is also good but requires one to keep the bottle in hand.

What I do before fast rides, is to open my Powerbars in advance—I suggest putting them in a plastic bag as they get messy in warm weather—because ripping open the wrapper can be tough. Once the wrapper is ripped it isn’t too hard to peel the bar with teeth.