DebRD_ATL said:

Fiber trials in this population are thin, and most of what gets quoted is extrapolated from idiopathic constipation in people eating normally.

Worth saying plainly that not all of this is benign. Severe constipation on delayed gastric emptying has produced obstruction and ileus cases, rarely but genuinely. Pain with vomiting and no bowel movement is not a fiber conversation.

NauseaFreeNow said:

Constipation replaced nausea at around week five and has been the more persistent of the two by a wide margin.

Gastroparesis symptoms with constipation: the delayed gastric emptying from GLP-1 agonists can cause early satiety, bloating, and feeling "full" for hours after a small meal.

Tips: eat your protein FIRST (most important macro), then vegetables, then carbs last. Chew thoroughly — 20-30 chews per bite isn't excessive. Avoid carbonated beverages with meals. If symptoms are severe, your doctor may recommend a gastric emptying study.

Dr.NateNeph said:

Worth saying plainly that not all of this is benign.

Drug interaction alert relevant to constipation: if you take oral levothyroxine (Synthroid), GLP-1 agonists can reduce absorption due to delayed gastric emptying. My TSH drifted up after starting semaglutide.

Solution: take levothyroxine on an empty stomach, 60 minutes before any food, and have your TSH rechecked 6-8 weeks after starting or changing GLP-1 dose. My endo had to increase my Synthroid by 12.5mcg.

A narrower follow-up, since the general answer is now clear:

Whether fiber actually helps GLP-1 constipation or whether the evidence is borrowed from a different population?

Closing the loop on my own question.

Resolved: water and magnesium first, soluble fibre second, bran gone entirely. Two months of doing it in the wrong order and a week to undo.