Benefiber and Metamucil are not the same product. They contain different types of fiber that work in fundamentally different ways in your body. Metamucil uses psyllium husk, a gel-forming fiber that absorbs water and adds bulk to stool. Benefiber uses wheat dextrin, a soluble fiber that dissolves completely in liquid and ferments in the gut. These differences matter for everything from digestive regularity to cholesterol management to blood sugar control.
Different Fibers, Different Jobs
Psyllium husk, the active ingredient in Metamucil, forms a thick gel when it contacts water. This gel holds onto moisture as it moves through your digestive tract, and it largely resists being broken down by gut bacteria. Because it stays intact, it physically bulks up your stool and keeps it soft. That’s what makes it effective as a laxative.
Wheat dextrin, the fiber in Benefiber, takes a completely different path. It dissolves invisibly in water (which is why Benefiber markets itself as taste-free and easy to mix into drinks). Rather than passing through intact, wheat dextrin gets fermented by bacteria in your large intestine. This fermentation feeds beneficial gut bacteria, giving it prebiotic properties. But it also means the fiber doesn’t stick around to bulk up your stool the way psyllium does. In fact, wheat dextrin does not provide a laxative effect and can actually be constipating in some people.
Which One Works Better for Constipation
If you’re looking for help with constipation, Metamucil is the stronger choice. Psyllium’s high water-holding capacity creates bulky, soft, easy-to-pass stools. It works because the fiber resists fermentation and remains present throughout the large bowel, physically retaining water in the stool.
Psyllium also has an unusual dual benefit: it can help with loose stools too. Studies show that psyllium reduces stool looseness without dramatically changing the water percentage, essentially normalizing stool consistency in both directions. This makes it useful whether you’re dealing with constipation or mild diarrhea.
Benefiber won’t give you this effect. Because wheat dextrin is fermented away by gut bacteria before it reaches the end of the colon, it simply isn’t there to hold water or add bulk. If constipation relief is your goal, Benefiber is the wrong tool.
Cholesterol and Heart Health
This is one of the biggest practical differences between the two products. Psyllium has a well-documented ability to lower cholesterol. In a head-to-head study comparing equal doses of psyllium husk and wheat dextrin taken three times daily before meals for three months, psyllium lowered LDL (“bad”) cholesterol by 17% and total cholesterol by 11%. Wheat dextrin produced no significant cholesterol reduction.
The FDA allows products containing psyllium to carry a health claim linking soluble fiber to reduced risk of coronary heart disease, provided each serving contains at least 1.7 grams of soluble fiber. Metamucil qualifies for this claim. Benefiber does not carry an equivalent heart health claim.
Blood Sugar Effects
The gel that psyllium forms in your gut slows the absorption of sugars from food, which blunts the blood sugar spike after meals. Clinical evidence shows psyllium reduces fasting glucose, hemoglobin A1c (a marker of long-term blood sugar control), and insulin resistance. It’s considered one of the most effective fiber types for glucose management.
Wheat dextrin acts as a prebiotic and may support gut health in ways that could indirectly influence metabolism, but results on blood sugar control have been mixed. If managing blood sugar is a priority for you, psyllium has a much stronger evidence base.
Gas and Bloating
Both fibers ferment more slowly than some alternatives like inulin (found in chicory root fiber supplements), which tends to produce the most gas. In lab studies, psyllium actually produced the lowest gas volume of the fibers tested, and neither psyllium nor wheat dextrin generated hydrogen concentrations significantly different from a control at most time points. Both had peak fermentation rates between 8 and 12 hours, compared to inulin’s faster 4-to-8-hour peak.
In practice, Metamucil can still cause bloating when you first start taking it or increase the dose too quickly, but it tends to be better tolerated than highly fermentable fibers. Benefiber is often marketed as gentler on the stomach, and because it dissolves completely, some people find it easier to take. But the fermentation data suggests neither product is dramatically worse than the other for gas production.
Mixing, Taste, and Convenience
Benefiber dissolves completely in liquid without changing the taste, color, or texture. You can stir it into coffee, soup, or water and barely notice it’s there. This is its main selling point for people who dislike the texture of fiber supplements.
Metamucil thickens whatever you mix it into. If you don’t drink it quickly, it turns into a gel. Many people find the texture unpleasant, though flavored versions help. Metamucil also comes in capsule form, which avoids the texture issue entirely but requires swallowing multiple capsules per dose.
One important safety note: psyllium-based products must be taken with at least a full glass of water (8 ounces). The FDA requires a choking warning on psyllium products because the fiber can swell and block the throat or esophagus if taken without adequate fluid. This risk is particularly relevant for anyone with difficulty swallowing. Benefiber doesn’t carry this same risk because it dissolves rather than forming a gel.
Gluten and Dietary Restrictions
Despite being derived from wheat, Benefiber contains less than 20 parts per million of gluten, which technically meets the FDA threshold for “gluten-free.” However, it is still not recommended for people with celiac disease. If you have celiac disease or a serious gluten sensitivity, Metamucil (which is wheat-free) is the safer option.
Both products are available in sugar-free versions. Metamucil’s original formulations often contain added sugar or artificial sweeteners for flavor, so check the label if that matters to you.
Choosing Between Them
Your choice depends entirely on what you’re trying to accomplish. Metamucil is the better option if you want help with constipation, loose stools, cholesterol reduction, or blood sugar management. It has stronger clinical evidence across all of these areas and carries FDA-recognized health claims that Benefiber does not.
Benefiber makes more sense if you’re primarily interested in prebiotic support for gut bacteria and want a fiber supplement that disappears into your food and drinks. It’s also easier to take if you have trouble with the texture of psyllium or can’t reliably drink a full glass of water with each dose. Just know that it won’t help with regularity the way Metamucil does, and it may even slow things down for some people.