Metamucil vs Citrucel for IBS: Which Fiber Supplement Works Better?

Metamucil vs Citrucel for IBS: Which Fiber Supplement Works Better?

By Dr. Onikepe Adegbola, MD PhD — Johns Hopkins-trained physician-scientist

Fiber supplements are one of the first things gastroenterologists recommend for IBS — and one of the first things patients struggle with. "I tried fiber and it made me worse" is something I hear weekly. The problem usually isn't fiber itself. It's the wrong type of fiber for your specific gut.

Metamucil and Citrucel are the two most popular fiber supplements in the US, and they work through fundamentally different mechanisms. Choosing the wrong one can genuinely make your IBS worse. Here's how to pick the right one.

Key Takeaways

• Metamucil (psyllium) is a soluble, fermentable fiber — effective but can increase gas and bloating in some IBS patients
• Citrucel (methylcellulose) is a soluble, non-fermentable fiber — generally better tolerated and less likely to cause gas
• For IBS-C (constipation), both work, but psyllium has stronger clinical evidence
• For IBS-D (diarrhea), Citrucel is often better tolerated because it doesn't increase gas
• If Metamucil causes bloating, switch to Citrucel before giving up on fiber entirely
• For a low FODMAP, gut-friendly psyllium option, look for formulas without added sugars or artificial sweeteners

Quick Comparison

Feature	Metamucil	Citrucel
Active ingredient	Psyllium husk	Methylcellulose
Fiber type	Soluble, gel-forming, fermentable	Soluble, gel-forming, non-fermentable
Causes gas/bloating	Can, especially initially	Minimal — non-fermentable
Prebiotic effect	Yes — feeds gut bacteria	No — passes through without fermentation
Best for	IBS-C, cholesterol, blood sugar	IBS-D and IBS-M, gas-sensitive patients
Clinical evidence for IBS	Strong (multiple RCTs)	Moderate (fewer studies)
Low FODMAP	Psyllium itself is low FODMAP per Monash	Methylcellulose is not tested by Monash but generally tolerated
Taste/texture	Gritty, thickens quickly	Smoother, dissolves better
Price (per month)	$10-15	$12-18

Metamucil (Psyllium): The Evidence Leader

Psyllium husk is the active ingredient in Metamucil, and it has more clinical evidence supporting its use in IBS than any other fiber supplement. A 2014 systematic review in the American Journal of Gastroenterology by Moayyedi et al. analyzed 12 randomized controlled trials and concluded that psyllium significantly improved overall IBS symptoms, with a number needed to treat (NNT) of 7 — meaning for every 7 patients who took psyllium, one experienced meaningful improvement.

How it works: psyllium absorbs water and forms a viscous gel in your intestine. This gel adds bulk to stool, which helps both constipation (by making stool easier to pass) and diarrhea (by absorbing excess water). It's genuinely effective for both IBS-C and IBS-D, which is unusual for a single intervention.

The downside: psyllium is fermentable. Your gut bacteria can partially ferment it, producing gas. For many IBS patients — especially those with visceral hypersensitivity — this gas production causes bloating, distension, and pain. In my practice, I estimate about 30% of IBS patients who try Metamucil report worse bloating in the first 1-2 weeks.

The trick: start very low (half a teaspoon) and increase gradually over 2-3 weeks. Most patients who push through the initial adjustment period do well. Those who can't tolerate it at all should switch to Citrucel.

Citrucel (Methylcellulose): The Gentle Alternative

Methylcellulose is a semi-synthetic fiber derived from plant cellulose. Unlike psyllium, it's non-fermentable — your gut bacteria can't break it down, so it doesn't produce gas. This makes it the better choice for patients who can't tolerate psyllium's gas-producing properties.

The clinical evidence for methylcellulose in IBS is less extensive than psyllium's, but the mechanistic rationale is sound. It works the same way — forming a gel, adding bulk, absorbing water — without the fermentation side effect. A smaller body of clinical data shows benefit for both IBS-C and IBS-D.

In my experience, about 80% of patients who failed Metamucil due to bloating tolerate Citrucel well. It's my second-line fiber recommendation and my first-line recommendation for patients who are extremely gas-sensitive or who have SIBO history (where additional fermentable substrates are counterproductive).

The downside: because it's not fermented, it doesn't provide the prebiotic benefit that psyllium does. Psyllium feeds beneficial gut bacteria and has been shown to increase short-chain fatty acid production (butyrate, specifically), which is beneficial for colon health. Citrucel passes through without feeding anything. If your goal is both symptom relief AND microbiome support, psyllium has the edge — if you can tolerate it.

Which Should You Choose?

Start With Psyllium (Metamucil) If:

• Your primary issue is constipation (IBS-C)
• You want the prebiotic microbiome benefits alongside symptom relief
• You also have high cholesterol (psyllium is FDA-approved for cholesterol reduction)
• You're willing to start low and increase slowly over 2-3 weeks
• You don't have active SIBO

Start With Citrucel If:

• Gas and bloating are your primary complaints
• You tried Metamucil and it made bloating worse
• You have IBS-D (diarrhea-predominant) and are worried about fermentation worsening loose stools
• You have a history of SIBO (you don't want additional fermentable substrate)
• You prefer a smoother texture that dissolves more easily

A Better Psyllium Option

One issue with Metamucil specifically (not psyllium in general): the brand adds sugar, artificial sweeteners (aspartame in some versions), or artificial colors depending on the formulation. These additives can independently trigger IBS symptoms. If you want psyllium without the junk, look for a clean formulation like Casa de Sante's Psyllium Fiber — it's physician-formulated, non-GMO, and low FODMAP without added sugars or artificial sweeteners.

For patients who need broader digestive support, the Low FODMAP Herbal Motility Support combines gentle natural motility agents for a different approach to regularity.

How to Take Either Fiber Supplement Properly

1. Start low — Half the recommended dose for the first week
2. Drink water — At least 8 oz with each dose. Fiber without adequate water can worsen constipation or cause an intestinal blockage in rare cases.
3. Increase gradually — Add a quarter dose each week until you reach the full recommended amount
4. Be consistent — Daily use works better than occasional use. Your gut adjusts to regular fiber intake.
5. Time it right — Take it 30-60 minutes before meals or at bedtime. Some patients do best splitting the dose — half in the morning, half at night.

FAQ

Can I take Metamucil and Citrucel together?

There's no safety issue, but there's also no good reason to combine them. If one isn't working, switch to the other rather than stacking both. The combination would add more total fiber than most IBS patients need.

Is Metamucil or Citrucel better for diarrhea?

Citrucel is generally better tolerated for IBS-D because it doesn't produce gas as a byproduct. Both absorb water and can help firm up loose stools, but the gas from psyllium fermentation can worsen symptoms in diarrhea-predominant patients.

Does Metamucil cause bloating?

It can, especially in the first 1-2 weeks. Psyllium is partially fermented by gut bacteria, producing gas. Starting at a low dose and increasing gradually reduces this effect. If bloating persists after 2-3 weeks of gradual increase, switch to Citrucel. For more on managing bloating, see our complete guide to gas and bloating triggers.

Is psyllium low FODMAP?

Yes. Monash University has tested psyllium husk and confirmed it is low FODMAP in a standard serving. However, Metamucil brand products may contain added ingredients (sugar, artificial sweeteners) that can be problematic. Choose a clean psyllium product without additives. Read our best low FODMAP fiber supplements guide for more options.

This article is for informational purposes only and does not replace personalized medical advice. Fiber supplement recommendations should be tailored to your specific IBS subtype and symptoms. Consult your gastroenterologist before starting or changing fiber supplements, especially if you have a history of bowel obstruction or narrowing.