Fiber supplementation for GLP-1 constipation — need advice

PurityPaulOR 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.

Dr.SurgeonPGH said:

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

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.

Dr.MetabolicMD 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:

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

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

Update — the osmotic agent was the thing. I had been reaching for a stimulant, which was making the next day worse.