You can raise the hormone. Fibers ferment in the gut and circulating GLP-1 goes up, and that part is not in dispute. What has never been shown is that the rise makes you full. Across 52 human studies, the link between a reported rise in GLP-1 and reported satiety sits at an odds ratio of 2.95. The interval runs from 0.87 to 9.98 [1]. That interval includes no effect at all.
A large supplement market rests on the opposite assumption. Its pricing side is covered in the supplements nobody prices, and its evidence side is this page.
What the review actually contains
Fifty-two studies across 1,085 participants, with a median of 19 people per study. The review was pre-registered, which is worth saying because most writing in this category is not.
Seventy-one percent of the included studies were acute interventions. They measured blood levels and reported fullness in the hours after a single dose. That is a reasonable way to study a mechanism and a poor way to study weight management, which happens over months.
Which fibers, if any
One category stood out. Dextrins showed effects on both GLP-1 and satiety, across four and five positive studies respectively, which the authors describe as promising for future research.
Beta-glucans and mannans each moved one outcome or the other without moving both. Those counts are small enough that a single additional trial could change the picture.
The rest of the supplement aisle
A separate narrative review names eight categories of supplement as adjuncts during GLP-1 treatment [2]. It is written for people already on the drug rather than for people avoiding it.
None of those categories appears in any monthly figure this desk publishes. The only concrete number the review gives is a protein target, which is set out with its sources in how much protein you need. A shopping list with no price attached is not a cheaper option; it is an unpriced one.
What the drug does that fiber has not been shown to do
The comparison worth making is about size of effect. Across 19 trials of high-potency incretin therapy, lab screening flagged low lymphocyte counts in 2.90% of participants against 1.77% on placebo [3]. Investigators recorded clinical malnutrition in 0.12%.
Those are small percentages and they are evidence of something large. Intake falls far enough on the drug that bloodwork registers it, which is the gap set out in reported against measured. Nothing in the fiber literature produces an effect of a size anyone has had to screen for.
The use the authors actually propose
Tapering, not substitution. They frame endogenous GLP-1 as relevant to people coming off the drugs rather than to people avoiding them.
That is a sensible question given how much weight returns after stopping, described in the regain numbers and about a third reach one year. Whether fiber helps with it is untested. It is still a better question than selling fiber as a replacement. What the drugs cost, for comparison, is in what a GLP-1 actually costs.