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Are Fiber Supplements a Healthful Substitute for Dietary Fiber?

By Carrie Dennett, MPH, RDN

Adequate dietary fiber intake has been linked to reduced risk of CVD, type 2 diabetes, and colon cancer, as well as improved digestive function.1,2 The 2020–2025 Dietary Guidelines for Americans recommends consuming 14 g of fiber per 1,000 kcal. That’s about 25 g per day for women and 38 g for men.3 However, the average intake is only 10 to 15 g per day. Are fiber supplements a suitable alternative?

High-fiber foods such as beans, lentils, vegetables, fruits, whole grains, nuts, and seeds include an array of nutrients in addition to their fiber, whereas fiber supplements have only the benefit of fiber.4 That’s why fiber supplements aren’t intended to completely replace high-fiber foods. However, when a client or patient finds it challenging to eat enough fiber through foods, these supplements can bridge the gap. Here’s some essential information about the types of fiber found in commonly used supplements.

Wheat Dextrin
Wheat dextrin is a soluble, nonviscous, fermentable (prebiotic) fiber that’s used as a thickener in many foods, as well as in fiber supplements. For example, Benefiber’s Original formula, Stick Packs, Chewables, and Healthy Shape all contain wheat dextrin. Wheat dextrin is starch and a byproduct of the processes that extract gluten from wheat and is safe to be ingested daily. While Benefiber’s wheat dextrin-based products contain less than 20 ppm of gluten, which technically makes them gluten-free, they’re not recommended for people with celiac disease.

Guar Gum
Benefiber’s Advanced Digestive Health Prebiotic Fiber + Probiotics formula uses partially hydrolyzed guar gum instead of wheat dextrin. Guar gum is a soluble, viscous (gel-forming), fermentable fiber derived from the bean, or seed, of the guar plant. Sunfiber is a brand of guar fiber, which also is derived from the guar bean, although guar fiber isn’t viscous. Guar fiber produces short-chain fatty acids in the gut when it’s fermented, but unlike many soluble fibers that ferment rapidly, guar fiber ferments slowly, reducing the chance of producing gas, bloating, or discomfort. This makes Sunfiber and other products that contain it, such as Regular Girl, an appropriate source of soluble fiber for people on a low-FODMAP diet for irritable bowel syndrome.

Inulin
Inulin is a soluble, viscous, fermentable fiber that’s extracted from onions, chicory root, and some other foods, and is incorporated in many processed foods to add fiber. Benefiber’s Prebiotic Gummies and Probiotic + Prebiotic Gummies use a combination of inulin and soluble corn fiber. A 2022 Stanford University study found that high doses (30 g) of inulin caused inflammation in most participants—but a decrease in one participant—and three experienced a spike in a liver enzyme. This was likely due to differences in the gut microbiome.5 It’s important to note that inulin and foods containing it are high-FODMAP.

Methylcellulose
Citrucel contains methylcellulose fiber, which is a soluble, viscous, nonfermentable fiber that’s extracted from wood pulp. It stays intact in the intestines, adding bulk to the stool, which is why it’s typically used to relieve constipation. However, individuals shouldn’t ingest it every day for chronic constipation, as constipation lasting longer than seven days may indicate a more serious health problem. Because methylcellulose doesn’t ferment, it’s less likely to cause gas and bloating.

Psyllium
Psyllium is extracted from the seeds or husks of the Plantago ovata plant. Psyllium seed husk is the coat surrounding the psyllium seed, and about 80% of the husk’s fiber is soluble, viscous, and nonfermentable fiber. It has the ability to absorb about 10 times its weight in water and forms a gellike coating on the intestinal wall, which facilitates passage of stool. The rest of the husk’s fiber is insoluble and can add bulk to stool.

Psyllium is used in supplements and fiber drinks and is added to many foods as a fiber booster or thickening agent in high fiber cereals, instant noodles, ice cream, rice cakes, and some baked goods. It’s important to note that only three of eight psyllium products tested by ConsumerLab were approved, with lead contamination the primary reason for failure. ConsumerLab’s top picks were NOW Psyllium Husk Caps and Yerba Prima Psyllium Whole Husks.6 A class action lawsuit was filed in December against the makers of the orange powder forms of Metamucil, which contain psyllium husk, because the company failed to disclose that the products “contain dangerous levels of lead.”7

Bottom Line
Taking fiber supplements daily appears to be safe, but clients and patients should drink an adequate amount of fluids each day and avoid taking more of the supplement than is recommended on the label. In addition, patients with a history of intestinal disorders should take fiber supplements only under the supervision of their health care team. It’s also important to check whether fiber supplements will affect medications patients are taking. For example, fiber supplements can lower blood glucose levels, so patients with diabetes may need to have their dose of insulin or other medications adjusted.

— Carrie Dennett, MPH, RDN, is the nutrition columnist for The Seattle Times, owner of Nutrition By Carrie, and author of Healthy For Your Life: A Non-Diet Approach to Optimal Well-Being.

References

1. Reynolds A, Mann J, Cummings J, Winter N, Mete E, Te Morenga L. Carbohydrate quality and human health: a series of systematic reviews and meta-analyses. Lancet. 2019;393(10170):434-445.

2. McRorie JW Jr. Evidence-based approach to fiber supplements and clinically meaningful health benefits, part 2: What to look for and how to recommend an effective fiber therapy. Nutr Today. 2015;50(2):90-97.

3. Dietary Guidelines for Americans, 2020-2025. U.S. Department of Agriculture and U.S. Department of Health and Human Services website. https://www.dietaryguidelines.gov/. Published December 2020.

4. McRorie JW Jr. Evidence-based approach to fiber supplements and clinically meaningful health benefits, part 1: What to look for and how to recommend an effective fiber therapy. Nutr Today. 2015;50(2):82-89.

5. Lancaster SM, Lee-McMullen B, Abbott CW, et al. Global, distinctive, and personal changes in molecular and microbial profiles by specific fibers in humans. Cell Host Microbe 2022;30(6):848-862.e7

6. Psyllium fiber supplements review: find the best psyllium fiber supplement and avoid lead. ConsumerLab website. https://www.consumerlab.com/reviews/psyllium-supplements/psyllium/. Updated March 11, 2024. Last accessed March 29, 2024.

7. Joseph P. 60-day notice of intent to sue: for violations of the Safe Water and Toxic Enforcement Act of 1986. State of California Department of Justice website. https://oag.ca.gov/system/files/prop65/notices/2023-02365.pdf. Published August 2, 2023. Last accessed March 29, 2024.