Originally Posted by
TromboneAl
No objection. I think I generally drink enough during a ride, and usually pee once or twice on a 60 mile ride. But I am sometimes thirsty at night, and I'm trying to figure out why.
On longer rides with intensity or in heat, you go into fluid deficit. It has to do with the ability of the stomach to absorb a lesser amount than what you are. sweating out, the function of which is to keep your core temperature stable. Don't forget also that at higher intensity, you are breathing out larger quantities of moisture than, say, at tootling pace.
The ability of the stomach to enable absorption of fluid is dependent on electrolyte balance. That balance also has an influence on the uptake of some nutrients from the stomach.