Metamucil vs Benefiber: which one do you actually need?
These two sit next to each other on the shelf and look like competing versions of the same product. They aren't. Metamucil is psyllium husk, which absorbs water and forms a gel. Benefiber is wheat dextrin, which dissolves into liquid and disappears. That one difference - does it gel or not - decides almost everything else: what it treats, whether it makes you gassy, how it tastes, and whether it does anything for your cholesterol.
Quick Answer
For constipation, Metamucil is the stronger choice. Psyllium husk forms a gel that adds bulk and softens stool, and it is the fiber with an FDA-authorised heart health claim for lowering cholesterol. For mixing into things without noticing, Benefiber wins easily - wheat dextrin dissolves clear and tasteless into coffee, soup, or water, with no grit and no thickening. Many people also find it gentler at first. The catch is that wheat dextrin is highly fermentable, so it can cause more gas for some people, and it has no bulking or cholesterol claim. If neither is landing, the issue is usually dose escalation or water, not the brand.
The core difference in one table
| Metamucil | Benefiber | |
|---|---|---|
| Fiber source | Psyllium husk | Wheat dextrin |
| Type | Soluble, gel-forming, mostly non-fermented | Soluble, non-gelling, highly fermentable |
| Texture in liquid | Thickens, gets gritty if you wait | Dissolves clear, no texture |
| Constipation | Strong - bulks and softens | Weak - no bulking effect |
| Diarrhea / loose stool | Helps - the gel absorbs water | Little effect |
| Cholesterol claim | Yes - FDA-authorised for psyllium | No |
| Gas potential | Lower - poorly fermented | Higher - fully fermented in the colon |
| Mixes into food | Poorly - thickens everything | Excellently - invisible |
| Gluten | Naturally gluten-free | Wheat-derived, labelled gluten-free |
Metamucil: the gel is the whole point
Psyllium husk comes from the seed of Plantago ovata. It's unusual among fibers because it does two things at once: it absorbs a large amount of water and holds it as a gel, and it largely survives the trip through your colon without being fermented by bacteria.
That combination is why it works for constipation in a way most supplements don't. The gel adds bulk, softens what's there, and gives your gut something to actually move. It also explains the counterintuitive fact that psyllium is recommended for both constipation and loose stool - the gel normalises water content in both directions.
The low fermentation matters too. Most fiber gets eaten by gut bacteria, and the byproduct of that meal is gas. Psyllium is only partially fermented, which is why it typically causes less bloating than inulin or wheat dextrin at the same dose.
It's also the one fiber with an FDA-authorised health claim connecting it to reduced risk of coronary heart disease, on the basis of its effect on LDL cholesterol - which is why "helps lower cholesterol" appears on the packaging and not on Benefiber's.
The two things people get wrong with Metamucil
Not enough water. Psyllium works by absorbing water. If you don't provide it, it takes what it can find and the result is the opposite of what you wanted. Full glass, and another one after.
Drinking it slowly. It starts gelling the moment it hits liquid. Mix and drink promptly, or you'll be chewing it.
Benefiber: the one you don't notice
Benefiber is wheat dextrin - a soluble fiber produced from wheat starch. It dissolves completely, adds no thickness, no grit, and essentially no taste. You can stir it into coffee, yoghurt, soup, or a smoothie and not know it's there. For anyone who has gagged their way through a glass of psyllium, that alone is the argument.
Because it doesn't gel, it doesn't bulk. It's a fiber-intake supplement rather than a constipation treatment, and it's fair to say the marketing doesn't always make that distinction obvious.
Wheat dextrin is also fully fermentable, meaning your gut bacteria digest all of it. That's not inherently bad - fermentation is how fiber feeds the microbiome and produces short-chain fatty acids. But the byproduct is gas, and people who are sensitive often find that Benefiber, despite feeling gentler going down, produces more bloating a few hours later than psyllium does.
On gluten: wheat dextrin is derived from wheat but processed to remove gluten, and Benefiber is labelled gluten-free. If you have coeliac disease, confirm with your doctor and check the specific product's labelling rather than relying on a general statement.
Which one for your actual problem
Pick by symptom, not by brand
Constipation - Metamucil. Psyllium bulks and softens; wheat dextrin does neither.
Loose or unpredictable stool - Metamucil, for the same reason in reverse. The gel absorbs excess water.
You just want to hit your fiber target - Benefiber, because you'll actually take it. The best supplement is the one that doesn't feel like a chore.
You bloat easily - Metamucil, at a small starting dose. Its low fermentability is the advantage here, counterintuitive as it feels.
Cholesterol is the goal - Metamucil. Psyllium has the evidence and the authorised claim; wheat dextrin does not.
You want to add it to food - Benefiber. Psyllium will turn your soup into a solid.
Cost, roughly
Both are cheap per serving, and generics make them cheaper still. Plain psyllium husk powder - the same active ingredient as Metamucil, without the flavouring, sweetener, or branding - is typically the lowest cost per gram of fiber by a wide margin. Store-brand wheat dextrin does the same for Benefiber. If you're taking either daily and long-term, the generic is worth the ten seconds of label-reading.
The advice that applies to both
- Start at a third of the labelled dose. Almost every bad experience with fiber supplements is a dose escalation problem, not a product problem. Your gut bacteria need one to two weeks to adjust.
- Drink more water than feels necessary. Non-negotiable for psyllium, still a good idea for wheat dextrin.
- Separate from medications. Fiber can interfere with absorption of some drugs. The usual guidance is a two-hour gap either side - check with your pharmacist about anything you take daily.
- Supplements supplement. Neither of these delivers what a varied plant diet does. A scoop of psyllium is one type of fiber; a week of beans, oats, berries, and vegetables is dozens, plus the polyphenols and micronutrients that come attached. Use the supplement to close a gap, not to replace the food.
For the food-first version of this, see fiber supplements vs food, and psyllium husk benefits for a deeper look at the active ingredient in Metamucil.
How to know whether it's working
The honest answer is that most people have no idea how much fiber they were eating before they added a supplement, which makes it impossible to tell whether the scoop is closing a gap or padding an already-adequate intake. A daily target of roughly 25-38g depending on age and sex is the standard reference point, and the average intake in the US sits closer to 15g.
Track for a week before you decide anything. If you're at 12g, a supplement is genuinely useful. If you're at 30g and still constipated, the problem is probably water, movement, or something worth mentioning to a doctor - and another scoop won't fix it. That's the case for measuring first, which is what FiberUp is for.
Frequently Asked Questions
Is Metamucil or Benefiber better for constipation?
Metamucil. Its active ingredient is psyllium husk, which absorbs water and forms a gel that adds bulk and softens stool - the mechanism that actually relieves constipation. Benefiber's wheat dextrin dissolves completely and does not gel, so it adds fiber to your intake without producing a bulking effect. Whichever you choose, drink plenty of water with it, because a fiber supplement without enough fluid can make constipation worse rather than better.
Which fiber supplement causes less gas and bloating?
Usually Metamucil, which surprises people because it is the thicker and more unpleasant one to drink. Psyllium husk is only partially fermented by gut bacteria, so less of it gets turned into gas. Wheat dextrin, the fiber in Benefiber, is fully fermentable, meaning your gut bacteria digest all of it and produce gas as a byproduct. That said, both can cause bloating if you start at a full dose - begin at about a third and build up over one to two weeks.
Can you take Metamucil and Benefiber together?
There is no particular reason to. They are both soluble fibers, and taking two supplements makes it much harder to work out which one is causing an effect if something goes wrong. If your total fiber intake is genuinely low, it is better to raise the dose of one supplement gradually and add fiber from food. If you are taking any regular medication, check with your pharmacist first, since fiber can interfere with absorption of some drugs.
Is Benefiber safe if I am gluten intolerant?
Benefiber's wheat dextrin is derived from wheat but processed to remove gluten, and the product is labelled gluten-free. For most people with a gluten sensitivity that is fine. If you have coeliac disease, check the specific product's current labelling and confirm with your doctor rather than relying on a general statement, since formulations and labelling differ by region. Psyllium husk is naturally gluten-free and avoids the question entirely.
Related Articles
- Inulin vs Psyllium: Which Fiber Is Right for You?
- Psyllium Husk Benefits: What It Actually Does
- Fiber Supplements vs Food: Which Actually Works?
- The Best Fiber for Constipation
- Soluble vs Insoluble Fiber, Explained
- How Much Fiber Per Day Do You Actually Need?
Scope
Fiber values are approximate and drawn from USDA FoodData Central, manufacturer labels, and standard nutrition references; actual amounts vary by variety, formulation, portion size, and region, and manufacturers reformulate products regularly - check the label on the box in front of you. This article is general nutrition information, not medical advice. If you have IBS, IBD, diverticular disease, a history of bowel obstruction, or you are on a prescribed diet or medication, talk to your doctor or a registered dietitian before making big changes. FiberUp is made by the author of this site.