I absolutely, certainly see immediate problems within a day of my son slowing down by about about a quarter to a third of his normal poo "output" in a day.
He starts getting whiny and fractious. Then he starts misbehaving and not listening to us. The he starts getting major giggles; ammonia. Then he wakes up in the night; ammonia!
If I don’t catch it fast and raise the Oxy Powder, and he continues at the slowed pace, that’s what we get. I can usually titrate the dose up and down pretty accurately. 1 is the usual baseline. 1.25 is sometimes needed. 1.5 if things are clearly going wrong and 2 means I’ve messed something up and we’re in emergency mode!
If I don’t get on top of it immediately (the next meal) with extra AKG and some of the remaining Pteridin 4 I have, things come off the rails. Badly. Huge symptom flare, as above.
The symptoms resolve within a few minutes of him having a good big poo and we're done until the next time.
It clearly shows a desperately dysbiotic gut.
Incidentally, this kind of "constipation" is way, way below the current Rome IV diagnostic criteria for constipation but I think that once someone meets them they are in a very, very bad place and have been for a long time.
For more thoughts on how to manage constipation (while you try to fix the gut) see: Even If You Go Every Day You May Still Be Constipated (Really! Really!!)