Some links on our site may earn us a commission at no extra cost to you. Learn more.
This article is for general information only and isn’t medical advice. Talk with a doctor or pharmacist before starting any fiber supplement, especially if you take medication, are pregnant, or have a diagnosed digestive condition like IBS.
Published July 30, 2026. Updated October 10, 2026.
Not every fiber supplement does the same job in your gut. Picking the wrong type is a common reason people quit after one bloated, gassy week. Citrucel’s methylcellulose is the gentlest choice if gas and bloating are your main worry. That is because gut bacteria don’t ferment it at all. Metamucil’s psyllium husk gels with water and works for both constipation and loose stools, with a moderate gas profile. NOW Foods’ inulin is the cheapest per gram of fiber by a wide margin. However, it is also the most fermentable of the three. So it’s the one most likely to leave you gassy if you start at a full dose.
I have kept fiber powder in the pantry on and off for years. What I learned is that the starting dose matters more than the brand. A full scoop on day one is how most people give up on fiber.
At a glance: pick by what bothers you most
- Best for sensitive stomachs: Citrucel (methylcellulose) — non-fermentable, so it’s the least likely of the three to cause gas or bloating.
- Best all-around regularity fix: Metamucil (psyllium husk) — gels with water and is commonly recommended for both constipation and loose stools.
- Cheapest per gram, best for gut-bacteria feeding: NOW Foods Inulin Prebiotic Pure Powder — the least expensive of the three per gram. It is also the most likely to cause gas at higher intakes.
How Psyllium, Inulin and Methylcellulose Behave in Your Gut
The differentiator that matters most isn’t the brand — it’s fermentability. Psyllium husk gels on contact with water and largely resists being broken down by colon bacteria. That is why it’s marketed as working in both directions. It can firm up loose stools and also soften hard ones. Inulin, a plant fiber most often sourced from chicory root or agave, is the opposite kind of soluble fiber. It’s highly fermentable, meaning gut bacteria feed on it actively. That is the mechanism behind its “prebiotic” marketing, and also behind the gas it can cause. Methylcellulose is a manufactured, plant-derived fiber. Citrucel’s own product information describes it as 100% non-fermentable, so gut bacteria essentially can’t break it down.
Cleveland Clinic dietitian Kendra Weekley notes that inulin and other chicory-root fibers can cause gas and “uncomfortable bloating.” That risk is highest in concentrated supplement form rather than in whole foods. So it’s a meaningfully different risk profile than psyllium or methylcellulose. It’s the main reason we don’t recommend jumping to a full-strength inulin dose if your gut is already sensitive.
Verified label facts, side by side
| Supplement | Fiber type | Price* | Fiber per serving | Fermentability |
|---|---|---|---|---|
| Metamucil Original Coarse Powder (114 servings) | Psyllium husk | $26.99 (Walmart.com) | 2.4g soluble fiber per rounded teaspoon | Low — largely resists fermentation |
| NOW Foods Inulin Prebiotic Pure Powder (1 lb) | Inulin (blue agave, per NOW’s label) | $18.37 (Vitacost.com) | 4g total fiber (3.3g inulin/FOS) per teaspoon | High — a fermentable prebiotic fiber |
| Citrucel Caplets (100-count) | Methylcellulose | $25.43 (Walmart.com, third-party seller) | 1g fiber per 2 caplets, per Citrucel’s own dosing | None — 100% non-fermentable per manufacturer |
*Prices are approximate, current as of publication, and change frequently — confirm the latest price with the retailer before buying.
The real cost per gram of fiber
Sticker price is misleading here because serving sizes and fiber content per serving are all different. We took each product’s confirmed price, servings per container, and fiber grams per serving. From those we calculated the cost per gram of actual fiber, a number none of these three brands publishes.
| Supplement | Servings per container | Price per serving | Cost per gram of fiber |
|---|---|---|---|
| Metamucil (psyllium) | 114 | $0.24 | $0.10 |
| NOW Foods Inulin | ~114 (per NOW’s label; 1 lb at 4g/tsp) | $0.16 | $0.04 |
| Citrucel (methylcellulose) | 25 four-caplet doses (100 caplets) | $1.02 per 2g-fiber dose | $0.51 |
The gap is stark. NOW Foods Inulin costs roughly a twelfth of what Citrucel costs per gram of fiber ($0.04 against $0.51). Metamucil lands in between. That’s not a knock on Citrucel’s effectiveness, though. Caplets are simply a more expensive delivery format than bulk powder, the same way pill-form vitamins cost more per nutrient. If cost per gram decides it and your gut tolerates a fermentable fiber, inulin wins by a wide margin. If you specifically need the caplet format because you can’t tolerate mixing a powder, that convenience carries a real price.
Metamucil (psyllium husk): the two-way regularity fix
Psyllium is the most-studied fiber supplement on this list and the one most doctors mention first for general regularity. It gels in water rather than fermenting quickly, which is why it’s used for both constipation and loose stools. The gel adds bulk to loose stool and also softens hard stool by holding water. Metamucil’s own label lists 2.4g of soluble fiber per rounded teaspoon, with dosing up to three times daily.
- Pros: Works in both directions (constipation and diarrhea). Moderate, well-tolerated gas profile for most people. The most widely recommended fiber supplement by clinicians.
- Cons: Must be taken with a full 8 oz glass of liquid or it can swell in the throat. Per Drugs.com, take oral medications at least 2 hours before or after psyllium, since it can interfere with absorption. Also costs more per gram of fiber than inulin.
Best for: anyone who wants one supplement for both ends of the regularity spectrum. It also suits people who can take other medication at a different time of day.
NOW Foods Inulin: the cheapest fiber, if your gut can take it
Inulin is a prebiotic fiber, and NOW’s organic powder is made from blue agave, per its label. Its whole selling point is that gut bacteria ferment it actively. That fermentation is what feeds a healthier gut microbiome, per the prebiotic research this ingredient is best known for. However, the trade-off is built into the same mechanism. More fermentation means more gas for many people, especially at a full dose taken all at once.
- Pros: Lowest cost per gram of fiber of the three by a wide margin. Feeds beneficial gut bacteria as a genuine prebiotic. Dissolves into hot or cold liquids and is largely tasteless.
- Cons: The most likely of the three to cause gas and bloating, per Cleveland Clinic. No published guidance here on drug-interaction timing the way psyllium has, so ask a pharmacist if you take other medication. Also not marketed or dosed for acute constipation relief the way psyllium is.
Best for: budget-conscious buyers who want general daily fiber and gut bacteria support. Expect to start small and increase slowly to manage gas.
Citrucel (methylcellulose): built specifically to skip the gas
Methylcellulose is a manufactured cellulose derivative, not a plant fiber in the psyllium or inulin sense. Citrucel markets that difference directly. Because gut bacteria can’t ferment it, the company says it adds bulk without the gas fermentable fibers can cause. Two caplets deliver 1g of fiber per Citrucel’s own dosing information. A standard 4-caplet dose equals 2g, the same fiber amount as one scoop of the powder form.
- Pros: Non-fermentable, so it’s the gentlest option here if gas is your main complaint. The caplet format needs no mixing or water measuring. Dosing is predictable and consistent per caplet.
- Cons: Highest cost per gram of fiber of the three, by roughly 13x versus inulin ($0.51 against $0.04). Caplets mean swallowing several pills per dose rather than one mixed drink. It also lacks psyllium’s dual-direction (constipation and diarrhea) track record.
Best for: anyone who has tried psyllium or inulin and found the gas intolerable. It does cost more per gram for that gentler profile.
Fiber Supplement Dealbreakers to Check Before You Buy
- Medication timing. Psyllium specifically carries a documented interaction risk. Drugs.com advises taking other oral medications at least 2 hours before or after a psyllium dose. Ask a pharmacist about timing for any supplement if you take prescription medication.
- Start low, especially with inulin. The most common reason people abandon a fiber supplement is starting at a full dose on day one. All three of these products can cause temporary gas or bloating as your gut adjusts. Still, inulin’s fermentability makes this more likely than the other two.
- Hydration matters for psyllium specifically. Because it gels, psyllium needs a full glass of liquid with every dose. Taking it dry or with too little water is a known choking and throat-swelling risk, per the label warning.
How We Compared Each Fiber Supplement
Serving sizes, fiber content, and fermentability claims come from each brand’s product pages and labels (Metamucil, NOW Foods/Vitacost, and Citrucel). Current pricing was verified at Walmart.com and Vitacost.com as of publication. The bloating and fermentability context comes from Cleveland Clinic’s published guidance, attributed to registered dietitian Kendra Weekley. The medication-timing caution comes from Drugs.com’s psyllium interaction page. Finally, the cost-per-gram figures are our own arithmetic on those verified numbers, not a metric any of the three brands publishes. Read more about our approach on our editorial standards page. Prices are approximate, current as of publication, and change frequently — confirm the latest price with the retailer before buying.
Fiber Supplement FAQ
Which fiber supplement causes the least gas?
Methylcellulose, the fiber in Citrucel, causes the least gas because gut bacteria can’t ferment it. Psyllium (Metamucil) is a moderate middle ground. Inulin (NOW Foods) is the most likely to cause gas because fermentation is exactly how it works as a prebiotic.
Can I take a fiber supplement with my other medications?
Ask your pharmacist first. Psyllium specifically has a documented interaction risk. Drugs.com says to take other oral medications at least 2 hours before or after a psyllium dose. That keeps it from interfering with absorption.
Is inulin really the cheapest fiber supplement per gram?
Based on current pricing and each label’s serving size, yes. NOW Foods Inulin costs about $0.04 per gram of fiber, versus roughly $0.10 for Metamucil and $0.51 for Citrucel caplets. Powdered bulk formats are generally cheaper per gram than caplets across all three fiber types.
Do I need to drink extra water with all three of these?
Extra water matters most for psyllium, which gels and needs a full 8 oz glass per dose, per its label warning. Inulin and methylcellulose mix more easily into liquids, but staying well hydrated is good practice with any fiber supplement.
Should I start with a full dose of any of these?
No. Start with a partial dose and increase it over a week or two to avoid temporary gas and bloating. That matters most with a fermentable fiber like inulin. Talk to a doctor about the right starting point for your situation.
Which Fiber Supplement Should You Buy?
Buy Citrucel if gas and bloating are your dealbreaker and you don’t mind paying more per gram for that comfort. Buy Metamucil if you want the most broadly recommended, two-way regularity fix and can space it away from other medications. Choose NOW Foods Inulin if cost per gram and feeding your gut bacteria matter most. Just start small while your gut adjusts. For related picks, see our magnesium glycinate vs. citrate vs. oxide comparison and our sugar substitute breakdown. Our oat vs. almond vs. soy milk comparison sits in our Nutrition Basics section.
