Five fiber supplements on sale in the US, read off their own supplement facts and drug facts panels and assessed against published criteria: the fiber itself, the dose per serving against doses used in trials, and everything in the tub that is not fiber.
No. 1 · Best for reaching a psyllium dose used in trials without buying anything else along with it
Konsyl Daily Psyllium Fiber Powder
The best documented fiber type, sold as nothing but itself.
One ingredient: psyllium husk powder. The supplement facts panel lists a 1 teaspoon (6 g) serving as 5 g of dietary fiber, 3 g of it soluble, with no added sugars or sweeteners, taken one to three times daily. Two servings are 12 g of psyllium, which clears the 10 g of psyllium a day (5 g twice daily) used in the eight-week constipation trial described below, and they supply 10 g of dietary fiber with 6 g of it soluble. Three servings clear the 7 g of soluble fiber a day that the FDA psyllium health claim is anchored to. Sunfiber below reaches its own studied dose in a single scoop, and two products here put more fiber in one serving; what psyllium has that neither has is decades of trial evidence behind this specific fiber. The organic version carries the same numbers plus USDA Organic certification (Oregon Tilth on the label), and Konsyl's own product page adds a claim of NSF certification for it. Beyond those seals, no batch testing is disclosed. It is a coarse powder that thickens within a minute of mixing, which is the price of having nothing added to it. 27910
No. 2 · Best for people who cannot get psyllium down, or who are following a low FODMAP diet
Tomorrow's Nutrition Sunfiber
A full studied dose in one scoop, and the most third-party certification of anything here, behind a much narrower evidence base.
Partially hydrolyzed guar gum. The label lists one 7 g scoop as 6 g of dietary fiber with 0 g of total sugars and no other ingredients. That single scoop sits at the 6 g a day of PHGG used in the 12-week randomized trial in irritable bowel syndrome described below, with no second serving required to get there. The label carries Monash University Low FODMAP, Non-GMO Project Verified and Clean Label Project seals and states Informed Choice certification, which is more outside review than any other product in this ranking discloses. The limit is mechanical rather than commercial: guar gum is fermented in the colon, so it does not do the water-holding work that keeps psyllium intact the whole way through, and the trial record behind it is a handful of studies rather than decades of them. 311
No. 3 · Best for psyllium you can pick up in any US pharmacy
Metamucil 4-in-1 Fiber Powder, Unflavored (original coarse, made with real sugar)
The right fiber, carried in 4 g of added sugar per teaspoon.
Psyllium and sugar are the entire ingredient list. The panel lists 1 rounded teaspoon (7 g) as 3 g of dietary fiber, 2 g of it soluble, alongside 4 g of total sugars, all of them added. One teaspoon three times a day, the low end of the label's own directions, comes to 9 g of fiber, 6 g of it soluble, and 12 g of added sugars: about a third of the 28 g fiber Daily Value, and about a quarter of the 50 g added sugars Daily Value, from a fiber supplement. Sugar-free Metamucil powders exist and swap sucrose for aspartame or stevia, so the trade is which additive you would rather have. The fiber is not the problem here, which is why this ranks above products whose fiber does less. 712
No. 4 · Best for people whose main complaint about other fibers is gas
Citrucel Fiber Therapy powder (methylcellulose)
The smallest dose in the ranking, in the longest ingredient list, from the fiber with the thinnest trial record here.
Methylcellulose, listed in the drug facts panel as 2 g of active ingredient per dose, which is one heaping tablespoon of the regular powder or one rounded tablespoon of the sugar-free version, up to three times a day. Methylcellulose is a semisynthetic gel-forming fiber, and the case usually made for it is that it resists fermentation and so produces less gas than fermentable fibers. The dose is the catch: at the label maximum you are at 6 g a day of a fiber with a far thinner published record than psyllium. The powder is also the busiest formula here. The regular orange version lists sucrose, maltodextrin, FD&C Yellow No. 6 lake, titanium dioxide, riboflavin and soy lecithin among its inactive ingredients, and the sugar-free version swaps the sucrose for aspartame. No third-party testing is disclosed. 113
No. 5 · Best for raising total fiber intake without changing the taste or texture of food
Benefiber Original powder (wheat dextrin)
Genuinely invisible in a drink, from the fiber least likely to change anything about your stools.
Wheat dextrin, one ingredient, 0 g of sugars, and it dissolves clear in almost anything, which nothing else here does. The label in the federal database lists 3 g of dietary fiber, all soluble, in a 2 teaspoon (4 g) serving taken three times a day; the manufacturer's current pack label restates the same powder as a 4 teaspoon (8 g) serving with 6 g of fiber, so read the container in front of you rather than a number you found online, including this one. The reason it sits this low is the fiber, not the formula: in the review of fiber physics cited below, nonviscous fermentable fibers including wheat dextrin are the group that does not produce a laxative effect, and wheat dextrin is named among fibers that can be constipating. If your goal involves stools rather than a number on a nutrition app, that outranks the 6 g on the front of the tub. 114
Nobody in this ranking sent us a product, and we did not put any of them in a laboratory. What we did instead is read the manufacturers’ own supplement facts and drug facts panels, put the numbers next to the doses used in published trials, and rank on the gap. Most of what we read is linked in the references, which point at federal label records rather than at shops. Two figures are not linked, because they exist only on a manufacturer’s own page or pack: Konsyl’s NSF claim and Benefiber’s current pack serving. Both are named as such in the entry where they appear, so you can see which sentence rests on what.
Two things follow from doing it that way. The ranking rewards products that publish their numbers, and it penalizes products whose serving is small enough that reaching a studied dose means taking three or four of them a day.
What a studied dose looks like
The Daily Value used on US labels is 28 g of fiber a day.8 That is a whole-diet target, not a supplement target. None of these products is built to cover it on its own, and food is still where most of it has to come from.
For psyllium, the anchor we used is a randomized trial in chronic idiopathic constipation: 22 adults, psyllium 5 g twice daily or placebo for eight weeks. Stool frequency rose from 2.9 to 3.8 stools per week and stool weight from 405 g to 665 g on psyllium, with no measurable change in colon transit or anorectal function, and no change on placebo.2 Ten grams a day, in other words, moved stool frequency by about one extra stool a week. That is the size of effect the evidence supports, and it is worth knowing before you buy a tub expecting more.
A second psyllium anchor comes from regulation rather than a single trial. The FDA health claim linking soluble fiber to coronary heart disease risk specifies 7 g or more per day of soluble fiber from psyllium seed husk, and requires a qualifying food to supply at least 1.7 g of soluble fiber per serving.7 That is the number Metamucil’s own packaging is built around.
For partially hydrolyzed guar gum, the anchor is a randomized, double-blind, placebo-controlled study: 121 adults with irritable bowel syndrome randomized to 6 g a day of PHGG or placebo for 12 weeks. The bloating score fell further on PHGG than placebo (-4.1 versus -1.2, P = 0.03), the effect persisted four weeks after the last dose, and there was no significant difference in the overall severity or quality of life scores.3 One narrow benefit, at one specific dose.
Why the fiber itself decides the ranking
The most useful single idea in this literature is that “fiber” is not one substance with one behavior. A 2017 review in the Journal of the Academy of Nutrition and Dietetics sorts supplement fibers by physics rather than by marketing category. High-viscosity gel-forming soluble fibers such as beta-glucan, psyllium and raw guar gum produce the cholesterol and glycemic effects; nonviscous soluble fibers such as inulin, fructooligosaccharides and wheat dextrin do not. In the large bowel, only two mechanisms drive a laxative effect, and both require the fiber to resist fermentation and still be present in stool. Soluble fermentable fibers including inulin, fructooligosaccharides and wheat dextrin therefore do not produce a laxative effect, and the review names wheat dextrin among fibers that can be constipating.1
One conflict is worth naming, because it runs in a direction that suits the top of this ranking. The lead author of that review, JW McRorie, has published closely related reviews with a listed affiliation of Global Clinical Sciences at Procter and Gamble, the company that makes Metamucil.15 We use the review for its mechanical distinction between fiber types rather than as an endorsement of any brand, and that distinction is consistent with the independent meta-analyses below, which found the benefit in soluble fiber and not in bran.4
That single distinction explains most of the order above. Psyllium is at the top because it is a gel former that survives the colon. Wheat dextrin is at the bottom because it is fermented before it can do the mechanical job, whatever the gram count on the front of the pack says, and an inulin product would rank there for the same reason.
What the trial evidence supports, and what it does not
The honest summary is modest benefit, in specific groups, with a real side effect.
In irritable bowel syndrome, a meta-analysis of 14 randomized trials in 906 patients found a significant benefit for fiber overall (relative risk of remaining symptomatic 0.86, 95 percent CI 0.80 to 0.94). The benefit was confined to trials of soluble fiber, with an NNT of 7. Bran showed no effect (RR 0.90, 95 percent CI 0.79 to 1.03).4
In chronic idiopathic constipation, a meta-analysis of seven randomized trials found that 113 of 147 patients on fiber responded compared with 61 of 140 on placebo, with significant improvements in stool frequency and consistency. Flatulence was significantly higher on fiber than placebo, and the authors rated the overall quality of evidence low and flagged a high risk of bias.5
The 2023 joint guideline from the American Gastroenterological Association and the American College of Gastroenterology reflects exactly that. Fiber received a conditional recommendation for chronic idiopathic constipation, while polyethylene glycol, sodium picosulfate, linaclotide, plecanatide and prucalopride received strong ones.6 A fiber supplement is a reasonable first thing to try. It is not the strongest thing available, and no ranking of tubs changes that.
What we did not assess
There is no tablet or chewable in this ranking, and that is a gap rather than a verdict. We wanted one for readers who will not drink a powder. The chewables we looked at were either the same wheat dextrin pressed into a tablet with sweeteners and colors added, or inulin products we could not confirm were still on sale in the US at the time of writing. A product we cannot buy is a product we cannot rank, so the slot is empty until one earns it.
We did not run our own assays, so we cannot tell you what is in a given lot. Where a manufacturer publishes a third-party certification we said which one; where nothing is published we said so rather than inferring quality from packaging.
We also do not quote prices. Prices for these products move with pack size, retailer and promotion, and a dollar figure written today is wrong within weeks. The durable part of cost is arithmetic you can do from the label: how many servings a day it takes to reach a dose that was actually studied. On that measure, a psyllium powder at 5 g of fiber per teaspoon and a chewable tablet at 2 g of fiber per tablet are not in the same category, whatever they cost.
If you are going to take one
Start at the smallest serving on the label and build up over weeks rather than days; the flatulence signal in the constipation meta-analysis is the most reliably reproduced finding in this whole literature.5 Take these products with a full glass of liquid, because every label here warns that taking them without enough liquid risks choking. Bulk-forming fibers can also affect how well medicines are absorbed, which is why Metamucil’s own label advises taking it at least two hours before or after other medicines.12
And the boundary worth naming: a persistent change in bowel habit, rectal bleeding, unexplained weight loss, or constipation lasting more than a week is a reason to see a clinician, not a reason to buy a bigger tub. Several of these labels say so themselves.