This gets cited here weekly, usually second-hand, so it is worth setting out what it does and does not establish.
The mechanism is slowed transit plus reduced intake, and that combination determines which interventions work. Less food means less bulk, slower motility means more water reabsorbed, and the result is a smaller, drier, slower stool. Insoluble fiber adds bulk to a system that is already moving slowly, which is why it frequently makes things worse. Soluble fiber holds water and is the better first choice, and an osmotic agent works with the mechanism rather than against it.
Where I think it is weakest: the follow-up is short relative to how long people actually take these drugs, so durability is an assumption here rather than a finding.
What I actually want to know is what the mechanism is, because if it is transit rather than water then fiber is the wrong lever. Practical detail welcome, however dull — the duller the better.
Figures above are from the primary publication rather than the press summary. If a number here disagrees with one you have, post yours and we will work out which of us is reading a secondary source.
Dr.EndoIndy said:The mechanism is slowed transit plus reduced intake, and that combination determines which interventions work.
Agreeing with Dr.EndoIndy, and the qualification matters more than the agreement. The escalation order that reflects the mechanism: water and salt first, then soluble fiber, then magnesium or an osmotic agent, then a stimulant only briefly and only if the osmotic has failed. Stimulants first is the commonest error and the one most likely to end in a cycle of dependence.
Dr.EndoIndy 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.
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Shop Reference StandardsTaking the question as asked, rather than the general version of it. Fiber trials in this population are thin, and most of what gets quoted is extrapolated from idiopathic constipation in people eating normally. The extrapolation is not unreasonable but it is an extrapolation, and it fails specifically for insoluble fiber at low intake — the case that comes up here most often.
Correct me if the detail matters more than I have assumed.
Dr.BariatricHTX 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…
This matches mine closely enough to be worth saying so out loud. Posting only so the count is not one.