Helps with Constipation, Diarrhea, IBS, and Diverticular Disease

By Amber J. Tresca 

 Medically reviewed by Jonathan Purtell, RDN

 Fact checked by Lisa Sullivan, MS

Fiber supplements are nutritional products that are available over the counter at drugstores, health food stores, big box stores, and online. They come in a variety of formulations, including capsules, powders, and pills, and contain one of three types of fiber: psyllium, methylcellulose, or polycarbophil.1

Fiber supplements are typically taken to maintain a healthy digestive system, prevent or treat constipation, or help lower cholesterol and blood sugar. While generally regarded as safe, they can cause side effects such as bloating or gas, particularly if overused or not taken as directed.1

If you are considering taking a fiber supplement, this article will help you better understand the benefits, side effects, possible interactions, and appropriate dosing of each of the different supplement types.

Health Benefits of Fiber Supplement

Fiber is a type of carbohydrate that's naturally found in fruits, vegetables, legumes, and whole grains. Fiber is important for maintaining regular bowel movements and offers numerous other benefits that extend well beyond digestive health.2

The bottom line is that most people in the United States do not eat enough fiber from the foods they eat due in part to the high consumption of processed and fast foods in the typical American diet. Fiber supplements are one option if you are falling beneath the U.S. government's recommendations for the daily consumption of fiber.3

Office of Disease Prevention and Health Promotion. Dietary Guidelines for Americans 2020-2025.

Fiber supplements are not intended to replace fiber found naturally in food. But, if you are not getting enough—perhaps because you are getting older and are eating smaller meals—fiber supplements may be a reasonable option.

The potential benefits of fiber supplements include:

• Maintaining regular, healthy bowel movements1

• Preventing or treating constipation4

• Relieving symptoms of irritable bowel syndrome (IBS) or diverticular disease1

• Helping lower blood cholesterol (and, in turn, the risk of heart disease)5

• Helping lower blood sugar (to better manage or prevent type 2 diabetes)1

• Aiding with weight loss (as fiber is filling and has few calories)2

• Potentially reducing the risk of colon cancer5

Possible Side Effects

Fiber supplements are generally regarded as not only safe but beneficial to one's health. With that aid, there are potential side effects you may experience, including:6

• Gas

• Cramping

• Bloating

• Diarrhea or constipation if taken in excess

• Reduction of blood sugar level (which may require you to adjust doses if you are taking diabetes medications)

Some of these side effects (like gas, cramping, and bloating) tend to subside as your body adapts to the increased fiber intake.7

Possible Drug Interactions

Because of the ways fiber supplements increase bulk in the intestinal tract, they can potentially interfere with the absorption of certain medications or supplements, including:8

• Bile acid sequestrants like Questran (cholestyramine) or Colestid (colestipol)

• Diabetes medications like Diabeta (glyburide) and Glucophage (metformin)

• Tricyclic antidepressants like Elavil (amitriptyline) and Tofranil (imipramine)

• Tegretol (carbamazepine), an anti-seizure drug

Drug interactions like these may or may not be significant. Even so, it is important to speak with a healthcare provider before starting fiber supplements to ensure they are safe and appropriate for you.

Dosage and Preparation

Fiber supplements come in a variety of formulations, including powders to be mixed with water or another liquid or capsules to be swallowed whole. Fiber is also often added to foods like crackers, cookies, cereals, and bars.

Dosage will vary based on the product and the desired effects. It's generally advisable to start with a low dose and build up until you've reached the recommended total daily fiber intake, which should always take into account your dietary sources of fiber.

Psyllium

Made from the seeds of a plant in the Plantago genus, psyllium contains 70% soluble fiber (which turns into a gel, helping soften stools) and 30% insoluble fiber (which adds bulk to stool and aids with normal digestion).9

In the gut, psyllium undergoes fermentation to become a food source for the "good" bacteria. For this reason, psyllium can cause gas.4

Psyllium can be effective in treating constipation and IBS.9 It has roughly 20 calories per tablespoon.10 Brand names include Metamucil, Fiberall, Hydrocil, Konsyl, and Serutan. Most are sold in powder form and mixed with 8 ounces of water.

A typical dosage of psyllium is 5 to 10 grams (g) with meals at least once daily10

Methylcellulose

Methylcellulose is non-allergenic, non-fermentable fiber created from the cell walls of plants. It's a soluble fiber that pulls in water to create a softer stool. It is often used to maintain regular bowel movements and to treat constipation and some causes of diarrhea.11

Methylcellulose is sold under the brand name Citrucel and is available both as a caplet and powder. Regular Citrucel has roughly 60 calories per dose, while Sugar-Free Citrucel has 24 calories per dose.

The recommended dosage of Citrucel is as follows:11

• Caplets: Two 500-milligram (mg) caplets up to six times per day, followed by an 8-ounce glass of water

• Powder: A heaping tablespoon (roughly 2 grams) mixed with 8 ounces of water up to four times daily.

Polycarbophil

Polycarbophil is a soluble fiber that water in the intestinal tract and creates a bulkier, softer stool. It does not ferment and is not absorbed by the body. As such, there is less likely to be gas or bloating.12

Polycarbophil may be used to treat constipation and bowel movement irregularities, but it is not appropriate for people who with dysphagia (difficulty swallowing).12

Polycarbophil is sold under the brand names FiberCon, Fiber Lax, Equalactin, and Mitrolan. Most are around 10 calories per dose and come as either regular tablets or chewable tablets.

The typical dosage of polycarbophil is 625 mg per day, followed by an 8-ounce glass of water. For the treatment of acute constipation, you can take 1,250 mg up to four times per day with an 8-ounce glass of water12

What to Look For

When shopping for fiber supplements, you'll want to make sure it contains the type of fiber you want. Some supplements also have added sugar, salt, flavorings, or dyes, which you may want to avoid. For these reasons, make sure to check the ingredients listed on the packaging before making your purchase.

Which Fiber Supplement Is Best?

There is no strong evidence that psyllium, methylcellulose, or polycarbophil is inherently "better" than the other options or that pills, powders, or capsules are more or less effective.1

The choice of fiber supplement is ultimately a personal one, ideally made with input from your healthcare provider.

Summary

Fiber supplements can be used to add to the dietary fiber you get from food. They can help ensure regular bowel movements, treat acute bouts of constipation and help lower cholesterol and blood sugar. There is evidence that they can reduce the risk of heart disease and even colon cancer.

Fiber supplements contain either psyllium, methylcellulose, or polycarbophil. Each works slightly differently from the others with different doses but, as a group, they are generally regarded as safe for daily use. Side effects include gas, bloating, and cramping.

Sources

McRorie J. Evidence-based approach to fiber supplements and clinically meaningful health benefits, part 1. Nutr Today. 2015;50(2):82-89. doi:10.1097/nt.0000000000000082

Lyon M, Kacinik V. Is there a place for dietary fiber supplements in weight management? Curr Obes Rep. 2012;1(2):59-67. doi:10.1007/s13679-012-0016-9

Office of Disease Prevention and Health Promotion. Food sources of dietary fiber. In: Dietary Guidelines for Americans 2020-2025.

Jalanka J, Major G, Murray K et al. The effect of psyllium husk on intestinal microbiota in constipated patients and healthy controls. Int J Mol Sci. 2019;20(2):433. doi:10.3390/ijms20020433

Liu L, Wang S, Liu J. Fiber consumption and all-cause, cardiovascular, and cancer mortalities: a systematic review and meta-analysis of cohort studies. Mol Nutr Food Res. 2015;59(1):139-46. doi:10.1002/mnfr.201400449

Drugs.com. Fiber capsules side effects.

Academy of Nutrition and Dietetics. Fiber.

Harvard Health Publishing. By the way doctor? Will a fiber supplement interfere with my medications?

Bruma Jose M. Satiety effects of psyllium in healthy volunteers. Appetite. 2016;105:27-36. doi:10.1016/j.appet.2016.04.041

Metamucil. Metamucil FAQS.

PubChem. Methylcellulose.

Drugs.com. Polycarbophil.

University of California San Francisco. Increasing Fiber Intake.

By Amber J. Tresca
Amber J. Tresca is a freelance writer and speaker who covers digestive conditions, including IBD. She was diagnosed with ulcerative colitis at age 16.