Dietary fibers can increase stool weight. Some fibers resist degradation during gut transit and increase stool weight by binding water. Even fibers that are extensively fermented during gut transit can increase stool weight because the fermentation of fiber increases bacteria in the stool that also bind water.

The gut is also an important organ of hormonal communications. It communicates with the brain to tell us what to eat and drink and when we have had enough.3 The importance of the gut microflora in the prevention of obesity has only recently been considered. We accept the importance of the gastrointestinal microflora in health and disease.

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However, data from human studies are mixed as to whether there is a beneficial immune effect of prebiotics that is distinct from the alteration in microflora they cause. The success of prebiotics appears to lie in their ability to improve resistance to pathogens by increasing healthy species of bacteria such as bifidobacteria and lactobacilli. This lowers the gut pH to a level at which pathogens are no longer able to compete.

Increasing fiber has the following potential benefits:

  • Lowers total and LDL cholesterol4
  • Lowers blood sugar and improves glycemic responses to food intake

  • Improves satiety and helps with weight loss

  • Helps constipation5
  • Helps some forms of irritable bowel syndrome symptoms

  • Some types may have prebiotic effects and increase the presence of a healthy colon’s microflora.

Table 2 outlines which types of fiber supplements have specific, defined benefits. Those fibers listed in the table as fermentable have the potential to serve as prebiotics.

Table 2: Effects of fiber supplements that are not laxatives

Fiber source Common brands Predominant fiber type Gut health effect (softens/bulks stools) Lowers Cholesterol
  • Metamucil®
  • Konsyl®
  • Maalox daily fiber therapy®
  • Generics and others
  • Soluble
  • Viscous
Yes Yes
  • Citrucel®
  • Store brands and generics
  • Soluble
  • Nonviscous
Yes Minimal
Wheat dextrin/
resistant maltodextrin
  • Benefiber®
  • Store brands and generics
  • Soluble
  • Nonviscous
Yes Minimal
  • Fiber Choice®
  • Fibersure®
  • Generics
  • Soluble
  • Nonviscous
Yes; most of reported effect on changes
in microbiota


Dietary fiber plays a critical role in a person’s health. Habitual dietary fiber intake is generally low, so the first recommendation would be to consume at least 25 g per day of dietary fiber. Both insoluble fibers and soluble fibers are important to include in the diet. Many factors, in addition to fiber, affect gut health and may need to be assessed prior to use of supplemental fiber.

Fiber intake should be increased gradually to allow the digestive tract to adjust. Adequate fluid intake is important for both tolerance and effectiveness of fiber. The gradual introduction of fiber may also minimize the increase in intestinal gas, which can limit the acceptance of healthier levels of fiber intake by some people.

Joanne Slavin, PhD, RN, is a professor in the Department of Food Science and Nutrition, University of Minnesota-Twin Cities, in St. Paul.


  1. Slavin JL. Position of the American Dietetic Association: Health implications of dietary fiber. J Am Diet Assoc. 2008;108(10):1716-1731.

  2. Slavin J. Fiber and prebiotics: Mechanisms and health benefits. Nutrients. 2013;5(4):1417-1435.

  3. Kuo SM. The interplay between fiber and the intestinal microbiome in the inflammatory response. Adv Nutr. 2013;4(1):16-28.

  4. Threapleton DE, Greenwood DC, Evans CE, et al. Dietary fibre intake and risk of cardiovascular disease: Systematic review and meta-analysis. BMJ. 2013;347:f6879.

  5. McRorie JW, Fahey GC. A review of gastrointestinal physiology and the mechanisms underlying the health benefits of dietary fiber: Matching an effective fiber with specific patient needs. Clinical Nursing Studies. 2013;1(4):82-92.