LipidDoc_ATL said:

The mechanism is slowed transit plus reduced intake, and that combination determines which interventions work.

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.

cory_ATX said:

I added fiber, made it noticeably worse, and only later worked out that I had added the bulk without adding the water.

Heartburn management on constipation: Gaviscon before bed has been my savior. The delayed gastric emptying means stomach acid just sits there.

Don't ignore persistent heartburn — chronic acid exposure can damage your esophagus. If OTC remedies aren't cutting it after 2 weeks, see your doctor for something stronger. You shouldn't suffer through this.

PharmacoVig_BOS said:

Worth saying plainly that not all of this is benign.

Gastric emptying studies and constipation: semaglutide delays gastric emptying by ~40% at steady state, as measured by acetaminophen absorption testing and scintigraphy[1].

Clinically relevant implications:

• Explains early satiety and nausea
• Affects absorption of co-administered oral medications
• Creates aspiration risk for procedures under anesthesia
• Contributes to constipation via slowed GI transit

Importantly, the gastric emptying delay attenuates with continued use (tachyphylaxis), which correlates with the transient nature of GI side effects.

One thing that is still open after SarahChen_PharmD’s answer:

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

OP back with an update, since a thread like this is useless without one.

Water and magnesium first, soluble fiber second, and dropping the bran entirely. Resolved in about a week after two months of getting it backwards.