Fiber supplements

OTCs Today

Mary Warner

A patients’ first stop after being told to increase the fiber in their diet is often their neighborhood pharmacy. The benefits of fiber in the diet are well-known and include lowering blood glucose and blood cholesterol, reducing calorie intake, and increasing the frequency of bowel movements. But the number of options for dietary fiber supplements can make choosing one overwhelming.

FDA defines dietary fiber as certain naturally occurring fibers that are “intrinsic and intact” in plants, along with isolated or synthetic nondigestible soluble and insoluble carbohydrates that FDA has determined have beneficial physiological effects to human health. FDA doesn’t approve dietary supplements before they are made available, so the agency often doesn’t know when new products come on the market and can’t keep a complete list of all dietary fiber supplements sold in the United States. However, FDA regulations require listing the number of grams of dietary fiber on the nutrition label if a claim for fiber is included.

Fiber types

Dietary fibers are categorized as soluble and insoluble. Most high-fiber plant foods contain both soluble and insoluble fiber, making a balanced diet containing a variety of fiber-rich foods important for overall health.

Insoluble fibers are nonviscous and aren’t degraded or fermented in the colon. Insoluble fiber forms a gel in the digestive system and is passed in the stool, so it can be helpful for treating constipation. Good sources of insoluble fiber include whole wheat flour, wheat bran, nuts, beans, and vegetables such as cauliflower, green beans, and potatoes.

Soluble fibers are water soluble, but viscosity and fermentability differ among soluble fibers depending on their structural characteristics. Soluble fibers composed of highly branched polymers (e.g., inulin, fructooligosaccharide [FOS], other fructans, wheat dextrin) are nonviscous, while those composed of straight-chain linear polymers are viscous. Gel-forming soluble fibers (e.g., b-glucan, raw guar gum, pectin, psyllium) produce cross-links between linear polymers that increase viscosity and water-holding capacity. Most soluble fibers undergo fermentation by bacteria within the colon, providing a food source for the bacteria and supplying small amounts of absorbable calories. Psyllium is the most recognized nonfermentable soluble fiber. 

How much fiber is needed?

Adequate intake for total fiber is in the range of 21 g to 38 g daily, with amounts for women and older adults being lower than those for men and younger adults. The National Academy of Medicine recommends 21 g of fiber daily for women older than 50 years, 25 g daily for women 50 years or younger, 30 g daily for men older than 50 years, and 38 g daily for men 50 years or younger.

The American Heart Association recommends consuming at least 14 grams of fiber per 1,000 calories daily to promote heart health. However, research from the U.S. Department of Agriculture indicates that the actual daily mean fiber intake is only about 15 g to 16 g for women and about 17 g to 19 g for men.

Benefits of fiber in the diet

As noted above, fiber is associated with a lower risk of heart disease. A high-fiber diet also improves bowel health by increasing the weight and size of stool, making it easier to pass. It may also lower the risk of hemorrhoids, diverticulitis, and colorectal cancer, as well as lower cholesterol levels in the blood and lower BP. In patients with diabetes, fiber in the diet may slow the absorption of sugar and help improve blood glucose levels. In addition, a diet that includes both soluble and insoluble fiber may lower the risk of T2D. Finally, since high-fiber foods tend to be more filling than low-fiber foods, patients are likely to eat less and stay satisfied longer, leading to potential weight loss.

Dietary fiber supplements

For most patients getting insufficient fiber from food, dietary fiber supplements are useful. In 2016, FDA identified seven isolated or synthetic nondigestible carbohydrates that were determined to have health benefits and meet the regulatory definition of dietary fiber. These include b-glucan, cellulose, guar gum, hydroxypropyl methylcellulose, locust bean gum, pectin, and psyllium husk.

In the years since, FDA has indicated that manufacturers can include 11 additional nondigestible carbohydrates, including acacia (gum arabic), alginate, arabinoxylan, cross linked phosphorylated RS4, galactooligosaccharide, glucomannan, high-amylose starch (resistant starch 2), inulin and inulin-type fructans, polydextrose, resistant maltodextrin and resistant dextrin, and mixed plant cell wall fibers such as sugar cane fiber and apple fiber on nutrition and supplement facts labels. While the final rule has not been amended to include these, FDA has indicated that while it completes rulemaking, it intends to exercise enforcement discretion to allow manufacturers to include the amount of these additional fibers in the dietary fiber declaration.

What to tell your patients

Ensure that patients understand that it may take 3 to 5 days or longer for the effects of a high-fiber diet or fiber supplement to be seen. Significantly increasing dietary fiber may initially lead to erratic bowel movement frequency, flatulence, and abdominal discomfort, but gradually increasing fiber intake over a period of 1 to 2 weeks can improve tolerance. Also advise patients that when taking fiber supplements, they should drink eight 8-ounce glasses of fluids, preferably water, per day. Patients who are pregnant should drink an additional 10 ounces and patients who are lactating should drink an additional 25 to 35 ounces of fluid per day.

For more information, see the chapters on “Constipation” and “Functional and Meal Replacement Foods” in APhA’s Handbook of Nonprescription Drugs, available in the bookstore on pharmacist.com or in APhA OTC in PharmacyLibrary (www.pharmacylibrary.com).  ■