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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.
Not all fiber supplements do the same job in your gut, and 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, because it isn’t fermented by gut bacteria 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, but it’s also the most fermentable of the three, which is exactly why it’s the one most likely to leave you gassy if you start at a full dose.
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 — a prebiotic fiber that’s the least expensive of the three per gram, but the most likely to cause gas at higher intakes.
How these three fiber types actually 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, which is why it’s marketed as working in both directions: it can firm up loose stools and soften hard ones. Inulin, a chicory-root fiber, is the opposite kind of soluble fiber: it’s highly fermentable, meaning gut bacteria feed on it actively, which is exactly the mechanism behind its “prebiotic” marketing — and the mechanism behind the gas it can cause. Methylcellulose is a manufactured, plant-derived fiber that Citrucel’s own product information describes as 100% non-fermentable, so gut bacteria essentially can’t break it down at all.
According to Cleveland Clinic, registered dietitian Kendra Weekley notes that inulin and other chicory-root fibers can cause gas and “uncomfortable bloating,” particularly when taken in concentrated supplement form rather than eaten as part of whole foods. That’s a meaningfully different risk profile than psyllium or methylcellulose, and it’s the main reason we don’t recommend jumping straight 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 (chicory root) | $18.37 (Vitacost.com) | 4g total fiber (3.3g inulin/FOS) per teaspoon | High — a fermentable prebiotic fiber |
| Citrucel Caplets (100-count) | Methylcellulose | $19.95 (Walmart.com) | 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 own confirmed price, servings per container, and fiber grams per serving, and 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 | ~113 (1 lb at 4g/tsp) | $0.16 | $0.04 |
| Citrucel (methylcellulose) | 25 four-caplet doses (100 caplets) | $0.80 per 2g-fiber dose | $0.40 |
The gap is stark: NOW Foods Inulin costs roughly a quarter of what Citrucel costs per gram of fiber, and Metamucil lands in between. That’s not a knock on Citrucel’s effectiveness — caplets are simply a more expensive delivery format than bulk powder, the same way pill-form vitamins cost more per nutrient than a powder does. If cost per gram is your deciding factor 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 commonly used for both constipation and loose stools — the gel adds bulk to loose stool and 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, oral medications should be taken at least 2 hours before or after psyllium, since it can interfere with drug absorption; costs more per gram of fiber than inulin.
Best for: anyone who wants one supplement that handles both ends of the regularity spectrum, and who takes any 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 extracted from chicory root, and 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. The trade-off is built into the same mechanism: more fermentation means more gas production 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; not marketed or dosed for acute constipation relief the way psyllium is.
Best for: budget-conscious buyers looking to add general daily fiber and support gut bacteria diversity, who are willing 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, and Citrucel markets that difference directly: because gut bacteria can’t ferment it, the company states it’s built to add bulk without the gas that fermentable fibers can cause. Two caplets deliver 1g of fiber per Citrucel’s own dosing information, and 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 for anyone whose main complaint with fiber supplements is gas; caplet format needs no mixing or water measuring; predictable, consistent dosing per caplet.
- Cons: highest cost per gram of fiber of the three, by roughly 4x versus inulin; caplets mean swallowing several pills per dose rather than one mixed drink; doesn’t have psyllium’s dual-direction (constipation and diarrhea) track record.
Best for: anyone who has tried psyllium or inulin and found the gas intolerable, and doesn’t mind paying more per gram for a gentler profile.
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; 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 manufacturer’s own label warning.
How we compared
We did not test these three supplements ourselves. Serving sizes, fiber content, and manufacturer fermentability claims come directly from each brand’s own product pages and label information (Metamucil, NOW Foods/Vitacost, and Citrucel). Current pricing was verified at Walmart.com and Vitacost.com as of publication. The bloating and fermentability context is sourced to Cleveland Clinic’s published guidance, attributed to registered dietitian Kendra Weekley, and the medication-timing caution is sourced to Drugs.com’s psyllium interaction page. The cost-per-gram-of-fiber figures are our own arithmetic applied to 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.
Frequently asked questions
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, and 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, and Drugs.com recommends taking other oral medications at least 2 hours before or after a psyllium dose so it doesn’t interfere 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 $0.40 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 requires a full 8 oz glass per dose per the manufacturer’s label warning. Inulin and methylcellulose are generally easier to mix 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. Starting with a partial dose and increasing gradually over a week or two is the most common way to avoid temporary gas and bloating, especially with a fermentable fiber like inulin. Talk to a doctor about the right starting point for your situation.
Bottom line
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. Buy NOW Foods Inulin if cost per gram and feeding your gut bacteria matter most, and you’re willing to start small while your gut adjusts. For related picks, see our magnesium glycinate vs. citrate vs. oxide comparison, our sugar substitute breakdown, and our oat vs. almond vs. soy milk comparison in our Nutrition Basics section.
