I can’t say. I was just trying to go through the simplest equation, keeping in mind that one of the big causes of constipation can be dehydration, and knowing that drinking plain water doesn’t always result in that water optimally getting to all the systems that need it due to the osmolality (for all I know this has been debunked, or it could be less critical than I had been led to believe), so the factors could be
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that you’re starting at a hydration deficit (I lose 2-3 lbs every night while I sleep, and some is water), and/or
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that you’re not getting enough liquid back into your body during, and/or
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that you’re not getting enough liquid back into your body after the workout,
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maybe you’re peeing too much out (try some salt and sugar in pre and post-ride water?)
I lost 2 lbs during my 1 hr 45 min z2 ride this morning (drinking coffee and water during), so that’s a quart of water lost through sweat and pee. I also know that my body takes in water very effectively when I eat carbs. I’d maybe try drinking a big glass of water, maybe with some sodium citrate and a little maltodextrine or a teaspoon of honey, before bed. And, coffee makes me pee a lot, so I’d guess I probably need to drink more water after the session. Maybe I’d try to drink another glass of water after bread and jam (before the ride. I’m just spitballing here. I was probably chronically dehydrated for a lot of years, and not active at all, so doing any sweaty activity would hit me hard, so I know it can be bad. And when I started biking again, I would be drinking water like crazy during and after the rides, but still getting nauseous and splitting headaches in the evenings…until I started consistently using sodium and got the dosage dialed in. Changed my riding and recovery, for the good. Hope you figure it out soon.