Dr.RaviCardio said:

The escalation order that reflects the mechanism: water and salt first, then soluble fiber, then magnesium or an osmotic agent, then a stimulant only…

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.

Correct me if the detail matters more than I have assumed.

amsterdam_pete said:

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

Acid reflux and constipation: I developed GERD symptoms around week 7 that I'd never had before. The delayed gastric emptying means food and acid sit in your stomach longer.

Management that works for me: elevate head of bed 6 inches, don't eat within 3 hours of lying down, avoid trigger foods (tomato, citrus, spicy, chocolate), and famotidine 20mg at bedtime. Much better now.

InsuranceTom said:

Worth saying plainly that not all of this is benign.

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.

Following on from TinaHashiRN — and this may be the naive question:

What the mechanism is, because if it is transit rather than water then fiber is the wrong lever?

Reporting back.

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.