What Counts as Fiber? A Discussion on FDA Regulations (Part Two)

By Molly Knudsen, MS, RDN

A quick recap

The Food and Drug Administration (FDA) is giving the Nutrition and Supplement Facts panels a facelift! In part one of this two-part series we outlined some of the major changes coming to labels starting in 2020. One of those changes includes defining dietary fiber for the first time, which affects what types of carbohydrates can be labeled as fibers.

Part one ended with a few burning questions regarding this change, so we’re going to dive right in and tell you everything you need to know about what the new fiber regulations mean for you. 

What is a fiber according to the FDA?

The way that dietary fiber was previously claimed on labels was similar to a no-cut policy for a children’s sport team: All nondigestible carbohydrates could have made the roster. However, the new definition turned dietary fiber into a competitive varsity sport: All nondigestible carbohydrates can try out for the dietary fiber team, but only those meeting the FDA’s criteria will actually make the cut.    

“Dietary fiber is defined as nondigestible soluble and insoluble carbohydrates (with 3 or more monomeric units), and lignin that are intrinsic and intact in plants; isolated or synthetic nondigestible carbohydrates (with 3 or more monomeric units) determined by FDA to have physiological effects that are beneficial to human health.”1 

Naturally occurring fibers are “intrinsic and intact” nondigestible carbohydrates that are found—surprise—naturally in whole foods such as fruits, vegetables, and certain grains and cereals, which have been well-established to provide benefits to human health.1 Foods that contain these naturally occurring fibers may be classified as dietary fiber on the new label. However, unlike naturally occurring fiber, isolated or synthetic fibers are typically added to foods, and identifying those that have been shown to confer a health benefit in people was not as straightforward.

Carbohydrates added to food meeting FDA's definition of dietary fiber2

Beta-glucan soluble fiber
Psyllium husk
Guar gum
Locust bean gum 
Hydroxypropylmethylcellulose (HPMC)
Mixed plant cell wall fibers (a broad category that includes fibers like sugar cane fiber and apple fiber, among many others)
Inulin and inulin-type fructans
High amylose starch (resistant starch 2)
Galactooligosaccharide (GOS)
Resistant maltodextrin/dextrin
Cross-linked phosphorylated RS4

How did the FDA decide what qualifies as a fiber?

Now remember, this is the first time the FDA has officially defined dietary fiber. In combination with updates to the Nutrition and Supplement Facts panels, the FDA’s intent is to guide consumers in making more informed, and potentially more healthful, decisions about the products they choose to consume. So it’s not surprising that a key component of the dietary fiber definition requires that the fiber is associated with health benefits. 

Therefore, to determine which nondigestible isolated or synthetic carbohydrates aligned with the definition, the FDA conducted a scientific review, like a team tryout, on many of these aspiring carbohydrates. 

To make the team, scientific evidence surrounding isolated or synthetic dietary fibers had to demonstrate:3

  • At least one physiological benefit to health (e.g., lowering blood glucose, lowering cholesterol levels, lowering blood pressure, increasing frequency of bowel movements, etc.)
  • A benefit attributed to that specific fiber and not a combination of carbohydrates
  • A health benefit observed in studies with healthy participants, or in participants where the benefit could be reasonably expected in healthy participants 

Nondigestible carbohydrates did not make the team if the scientific evidence behind that carbohydrate showed that:3

  • Findings were inconsistent (e.g., the carbohydrate showed a benefit in some studies but not others) 
  • Evidence was insufficient, or there was no replication of study findings
  • Studies were only conducted in participants with a disease state, where the benefit could not be reasonably expected in healthy participants  

What does this mean for carbohydrates no longer considered dietary fibers?

Nondigestible carbohydrates that didn’t make the cut can no longer be claimed as dietary fiber on the Nutrition or Supplement Facts panels. If a food product containing a carbohydrate no longer classified as a dietary fiber previously declared a total of 10 grams of fiber and 4 grams were contributed by that carbohydrate, the updated dietary fiber claim would now be 6 grams. 

However, this does not necessarily mean that all of the nondigestible carbohydrates that didn’t make the dietary fiber cut are bad or unwanted ingredients in foods. Unless a product has been reformulated, the product’s contents will be the same; only the label will have changed. 

In addition, the FDA’s definition of dietary fiber allows flexibility for other nondigestible carbohydrates to be added as fiber as research evolves. Although dietary fiber is a varsity team, there is no limit to the number of players, so it’s possible that more nondigestible carbohydrates may be added to the list of dietary fibers in the future.  


    1. Nutrition labeling of food. FDA Code of Federal Regulations Title 21, Volume 2, Part 101. https://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfcfr/CFRSearch.cfm?fr=101.9&SearchTerm=nutrition%20label. Accessed December 19, 2019.  
    2. Questions and answers on dietary fiber. FDA.gov. https://www.fda.gov/food/food-labeling-nutrition/questions-and-answers-dietary-fiber#define_dietary_fiber. Updated June 13, 2018. Accessed December 5, 2019.  
    3. Scientific evaluation of the evidence on the beneficial physiological effects of isolated or synthetic non-digestible carbohydrates submitted as a citizen petition; draft guidance for industry; availability. Fed Regist. 2016;81(226): 84516-84517. To be codified at 21 CFR § 101.9.  

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