Get to know Fiber

All you need to know

It’s a great question that is still being asked today. So, what is fiber? The Institute of Medicine recognizes two types of fiber, both of which are found in the food we eat: dietary fiber and functional fiber. Dietary fiber is the non-digestible carbohydrates and lignin (a complex polymer) present in plants. Functional fiber is isolated non-digestible carbohydrates that have physiologic effects in humans. Together, the dietary and functional fiber in the food we eat make up total fiber.1,2


The USDA recommends total daily fiber intake of 14 grams of fiber per 1,000 kcal of food consumption.3 In simpler terms, that means an adult woman (between the ages of 19 and 50) should consume 25 grams per day while the average man (between the ages of 19 and 50) should consume 38 grams per day.2

What does it take to get enough total daily fiber on average? You can always eat 7 apples, 9 cups of carrots, 8 packets of oatmeal, 9 bananas, or 13 cups of broccoli. That’s quite a challenge! No wonder less than 5% of Americans get enough fiber from the foods they eat.4 In fact, the average adult consumes only about 50% of the recommended daily fiber.4,5

There is an easy solution to fill the fiber gap in most Americans’ diet: fiber supplements. Taking fiber supplements is a convenient way to increase your daily fiber intake, but not all fiber supplements provide the same benefits.6


There are 3 main properties that determine the health benefits of fiber:

    - Solubility: its ability to dissolve in fluids in the GI tract.6-9
    - Viscosity/gel formation: its ability to thicken and form gels when mixed with fluids (non-viscous, viscous, or gel-forming).6-9
    - Fermentability: the degree to which the fiber is degraded/digested by bacteria in the colon (forming gases and short chain fatty acids).6-9

    - Insoluble fibers are the fibers that do not dissolve in fluids. These types of fiber tend to provide benefits as large particles that remain undigested in the GI tract.
    - Soluble fibers are those fibers that dissolve in liquids, with benefits depending on how they act in liquids.6,7,9

Soluble fibers are further broken down based on what happens when they dissolve in liquids.

    - Soluble non-viscous completely dissolve without altering the physical properties of the liquid and are not noticeable in the liquid to the patient when viewed in a glass.
    - Soluble viscous fibers when dissolved in a liquid, increase the viscosity of the liquid over time, patients will notice a thickening of the liquid when viewed in a glass. The viscous nature of the fiber is important in determining the health benefits provided by each type fiber. Those that form a viscous gel, can help maintain healthy cholesterol and blood sugar levels.6,7,9

Fermentability is not limited to one specific type of fiber. Though in general insoluble fibers have limited fermentability, soluble non-viscous fiber are highly fermentable (serving as prebiotics), and the fermentability of soluble viscous fibers is dependent on the source; some are and others are not fermentable. The fermentation of fiber is an important factor in the patient’s experience, because gas is a by-product of fermentation. The body is able to process some gas production by fermentation, however rapid fermentation of fiber can lead to excess gas production and the corresponding side effects.6,7,9,10 This is why when starting a fiber regimen for your patients it is important to start at a low dose (3-4g/day 1st week) and slowly increasing the dose over subsequent weeks to ideal amount of fiber for the desired health benefit.6,10

You can see how common sources of fiber, including Metamucil, fit based on these criteria here.


1Anderson JW, Baird P, Davis RH, et al. Health benefits of dietary fiber. Nutr Rev. 2009;67(4):188-205.

2Institute of Medicine of the National Academies. Dietary reference intakes: macronutrients. 2002/2005. The National Academies Press. Accessed at: on June 12th, 2015.

3United States Department of Agriculture. Report of the dietary guidelines advisory committee on the dietary guidelines for Americans, 2010. May 2010. Available at Accessed June 11th, 2015.

4USDA WWEIA Report Dietary Fiber. Available at Accessed 07/24/2015.

5Park Y, et al. JAMA. 2005;294(22): 2849–2857.

6Chutkan R, et al. J Am Assoc Nurse Practitioners. 2012;24(8):476-487.

7McRorie J and Fahey G. Clinical Nursing Studies, 2013;1(4): 82-92.

8Dikeman CL, Fahey GC. Crit Rev Food Sci Nutr. 2006;46(8):649-663.

9McRorie JW Jr. Nurt Today 2015 50(2):82-89.

10McRorie JW Jr. Nurt Today 2015 50(2):90-97.