What's the definition of dietary fiber?

I know there’s a regulation for dietary fiber, but it’s so complicated I don’t know how to apply it.

It’s not surprising that the recently enacted regulatory definition of fiber is difficult for non-experts to understand. Dietary fiber has long been associated with health and the concept is simple enough. Eating fiber-rich foods promotes digestive health, which most of us associate with regularity, ie. laxation. But if asked to define fiber, few of us could articulate what it is. We may have vague notions about bran or whole grains as being fiber but are unfamiliar with the chemical structures involved. This lack of familiarity hampers our understanding of the highly-technical definition of dietary fiber that was recently incorporated into food label regulations.

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Key elements of the definition

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

21 CFR § 101.9(c)(I)(i)(6)(i))

The newest regulatory definition of dietary fiber was published by the FDA in the Code of Federal Regulations (CFR) on May 27, 2016 (Fed. Reg. 81(103:33852). This document is not light reading!

The first 225 pages contain the FDA’s answers to 543 comments that were received for the proposed changes to the food label. The actual amendments begin on page 33978 and continue for 21 pages. The definition of fiber is given on page 33979 (see inset).

The definition is consistent with those developed over several decades by other jurisdictions, as well as the CODEX Alimentarius Commission, an international body of scientists and delegates from many nations, including the United States. The FDA regulation defines the procedures for quantifying the fiber content of a food on the nutrition facts panel.

It is important to note that this process is separate from GRAS (Generally Recognized as Safe) requirements. That is, all ingredients used in food must comply with the FDA’s safety standards. But, to be claimed as fiber, foods must also comply with the new dietary fiber regulation.

Health Benefits

Example Health Benefits

Lower blood glucose, insulin, or cholesterol
Lower blood pressure
Improved laxation
Enhanced mineral absorption
Reduced energy intake

The key feature of the regulation is the distinction between naturally-occurring and manufactured dietary fibers. Non-digestible carbohydrate that is naturally present in food (i.e. intrinsic fiber) can be counted as dietary fiber.

There is no requirement to demonstrate the health benefits of intrinsic fiber as the existing literature firmly demonstrates its beneficial effects on health.

Non-digestible carbohydrate that is synthetically-produced or is extracted from its natural source and added to food must demonstrate a health benefit (see box) or it cannot be counted towards the total amount of dietary fiber claimed on the nutrition facts panel. The health benefits cited by the FDA are listed as examples, with the recognition that other benefits of fiber might arise in the future. For synthetic or extracted non-digestible carbohydrates to qualify as dietary fiber, at least one benefit must be demonstrated.

What fibers have been approved?

The FDA reviewed the published literature on the physiological effects of numerous synthetic and isolated non-digestible carbohydrates and deemed that sufficient evidence existed to support the health benefits of seven non-digestible carbohydrates and these were included in the published definition. Review of a further 26 non-digestible carbohydrates was published in 2016 and those deemed to have sufficient evidence to support a health benefit were announced in a subsequent publication in 2018. See both the current list and those carbohydrates that have been proposed as additions to that list below.

Isolated/synthetic non-digestible carbohydrates

Beta-glucan soluble fiber
Psyllium husk
Cellulose
Guar gum
Pectin
Locust bean gum
Hydroxypropylmethylcellulose

Proposed additions

Mixed plant cell wall fibers
Arabinoxylan
Alginate
Inulin and inulin-type fructans
High amylose starch (resistant starch 2)
Galactooligosaccharide
Polydextrose
Resistant maltodextrin/dextrin
Cross linked phosphorylated RS4
Glucomannan

Example: Why the FDA proposes High Amylose Starch as a dietary fiber

Take a look at the FDA’s review of 26 non-digestible carbohydrates. Immediately it is evident that some dietary fibers have much more evidence backing their benefits than others. Resistant Starch 2 (RS2) from high amylose corn starch has had numerous studies demonstrating its efficacy.

In their initial 2016 review, the below benefits were reviewed:

Blood Cholesterol

1/6 studies demonstrated a ↓ in blood cholesterol

Laxation

3/7 studies identified an improvement in laxation

Energy Intake

2/4 studies showed a ↓ in appetite or energy intake

Though these studies identified potential benefits, none of these qualified for why high amylose starch (RS2) is considered a dietary fiber

A second look: RS2 and blood insulin

Blood Insulin

6/40 studies showed a ↓ in post-prandial blood insulin without rises in blood glucose

In 2018, the FDA published an updated review on products meetings the dietary fiber definition. For high amylose starch, this meant a big update.

40 studies on dietary intake of RS2 and blood glucose/insulin were reviewed. After filtering out the irrelevant studies, they found that RS2 lowered the post-prandial insulin response without concurrent rises in post-prandial glucose. Such an effect is related to reduced risk of coronary heart disease, and thus a beneficial physiological effect of RS2. This led to the support of the FDA’s decision to propose RS2 as a dietary fiber.

Thus, it’s not necessary for all of the literature to align perfectly on the beneficial effects. However, there needs to be some level of scientific rigor to substantiate the benefits claimed. Here, there was enough regarding insulin, but not cholesterol, laxation, or energy intake.

Concluding Remarks

If you think your product should be classified as a dietary fiber, the answers to the below questions should be a resounding yes!

Is it a non-digestible carbohydrate or lignin?
Does it contain 3 or more monomeric units?
Is it intrinsic and intact in a plant?
If isolated or synthetic…
- Does it’s consumption exert a physiological effect beneficial to human health?

Navigating regulatory environments is frequently daunting. Once you know where to look, the pieces begin to fall together. If you’re working on a dietary fiber and trying to identify it’s health benefits, drop us a note! We’d love to hear what you are working on and help bring the research to fruition.

About the author: Christine Pelkman is a lecturer at Penn State and an advisor to Traverse Science who brings decades of experience from her roles at Ingredion and Campbell Soup managing clinical research programs and navigating the regulatory environment. She brings a keen eye for leveraging the science with regulatory precedence while keeping business goals at the forefront. Follow her on LinkedIn.

About the company: Traverse Science is a nutrition consulting firm working with ingredient suppliers and consumer packaged goods companies in the human and animal nutrition space. We work with clients to get science done, whether that means organizing and conducting a study, analyzing new or long-forgotten data, or writing a manuscript for peer review or guidance document for internal use. As teams change, time runs short, or projects pivot, we provide the muscle and the know-how to finish your nutrition science and get your projects out the door – whatever that means for you. We believe that science doesn’t have to be hard, and we’re here to make it easy. Follow Traverse Science on LinkedIn, and connect with us at engage@traversescience.com.

What’s the FDA regulatory definition of dietary fiber?