This is a collaborative article about fiber written by OHSU Dietetic Intern Rahda Moghe, MS and HealthyU Nutrition's Registered Dietitian Cary Cuevas, RDN, LD
Fiber is an essential and versatile nutrient. It is a type of carbohydrate that our body needs for optimal health. Fiber is a key nutrient that supports ideal gut health and helps maintain a healthy weight. It is a component of foods found only in plants and foods of plant origin.
The 2015 Executive Summary Scientific Report of the Dietary Guidelines for Americans states that “Fiber is a nutrient of public health concern.” Currently, in the US diets, calcium, potassium, dietary fiber, and vitamin D have been identified as nutrients of public health concern due to underconsumption of foods that are good sources of these nutrients (Current Dietary Guidelines | Dietary Guidelines for Americans, n.d.). A healthy diet needs to be a balanced diet.
What kinds of fiber are in foods? Why do we need fiber in our diets?
There are two main types of fiber: soluble and insoluble fiber.
Soluble fiber can form a gel as it dissolves in water, slowing digestion and thereby providing a more prolonged feeling of fullness (Mayo Clinic). Studies have shown that soluble fiber helps lower cholesterol and blood sugar levels (Mayo Clinic).
We do not digest or absorb most dietary fiber, so it passes mostly intact through our stomach, intestines, and colon. Despite our body's inability to digest most fiber, it offers many benefits for our gastrointestinal health. In our large intestine and colon, there are about 1500 types of beneficial bacteria. These bacteria, also called gut flora, ferment the undigested soluble fiber (Nelms & Sucher). The byproducts of this bacterial fermentation include energy in the form of short-chain fatty acids and lactate that support our gut flora as well as cells of the colon (Nelms & Sucher). Gases are also a byproduct of fiber fermentation. If there is excessive undigested fiber in the colon, this can cause discomfort in the form of flatulence and gas.
As the name suggests, insoluble fiber remains undissolved and mainly helps add bulk to digested food, help it move through the digestive tract, and prevent constipation (Mayo Clinic). A diet high in fiber (28-35 grams a day) can help with regular bowel movements and reduce the risk of hemorrhoids and other rectal problems (UCSF). Both soluble and insoluble fibers are essential for health (UCSF).
Where do we get fiber in our diets?
Plants get their structure and form from fiber and are the primary source of fiber in our diets. In addition to providing fiber, eating plant foods provides other carbohydrates, proteins, fats, minerals, vitamins, and other helpful bioactive compounds.
According to the Cleveland Clinic, you can incorporate fiber into your diet by adding more plant-based foods rich in soluble fiber, such as apples, bananas, citrus fruits, carrots, beans, peas, avocados, oats, and barley. Vegetables such as cauliflower, green beans, potatoes (with and without skin), whole wheat, wheat bran, beans, legumes, nuts, and seeds are good sources of insoluble fiber (Mayo Clinic How to Add More Fiber to Your Diet, n.d.).
Are there health benefits to functional fibers added to processed foods?
Some soluble and insoluble fibers, such as inulin, resistant starch, and psyllium, are functional fibers. While they naturally occur in foods, they are often added to processed foods or taken as supplements for their health benefits. Supplements such as Metamucil, which contains psyllium husk, can be taken daily to increase soluble fiber. A psyllium husk supplement may support improved gut health and regular bowel movements (Clinic, 2024b).
For various reasons, manufacturers now use functional fibers in foods that do not naturally contain or are considered low in fiber. Functional fibers added to food add desired texture, may increase shelf life, and enhance the healthfulness of foods. However, while these added fibers do appear to offer some of the added benefits of high-fiber foods when consumed as a whole, they should not be the primary source of fiber in a diet (2, 3). Two common functional fibers added to food include inulin and resistant starch.
Inulin, a soluble fiber, is found in onion, garlic, barley, Jerusalem artichoke tubers, and chicory root (Quin, Y.Q et al., 2023). The food industry extracts inulin from Jerusalem artichoke tubers and chicory root (Quin, Y. Q et al., 2023) to add to foods that are generally low in fiber. Inulin ingestion as an additive or supplement can sometimes cause side effects like gastrointestinal problems and allergies (Sheng W et al., 2023.). Inulin has been added to food products for its perceived healthfulness for over a decade. For example, FiberOne® products use inulin to increase the fiber content of their food products.
Over the past several years, more research has been conducted supporting the health benefits of adding inulin to lower-fiber foods. These include increasing the feeling of fullness to support healthy body weight and better blood sugar control. Inulin has also been shown to support the bacteria in our gut, which supports our immune system and may lower the risk of colon cancer. According to studies released in 2021 and 2023, certain probiotics, including inulin, may help improve mood and reduce the severity of depression.
Another common functional fiber is resistant starch. It is found naturally in some foods, like beans, peas, lentils, rice, and whole grains. Interestingly, we can increase the amount of resistant starch in many of these foods, particularly rice, by cooking and then cooling them before reheating them to enjoy.
Since the FDA approved Modified Wheat Starch, a resistant starch, as a fiber in 2019, it is increasingly being added to some processed foods. Like other fibers, resistant starch is a carbohydrate not digested in the small intestines but fermented in the large intestines by our gut bacteria. Modified wheat and modified food starch are added to traditionally lower-fiber foods, like tortillas, to increase the fiber content and decrease total calories. They are also a primary ingredient in Keto bread and baked products, along with other fibers like inulin and oat fiber. Modified wheat starch and inulin are considered non-digestible fibers, so they are not included in the “Net Carbohydrate” count or total calories on nutrition labels.
Consuming large amounts of Inulin, or any fiber, at one time will likely lead to GI distress, including bloating, gas, and flatulence. Some foods naturally low in fiber have up to 10 grams of added fiber per serving, which may be too much for many individuals if they are not used to consuming much fiber in one meal. While adding more fiber to your diet, up to 28-35 grams per day, is best for health, being cautious with how much we consume of foods high in added fiber can help reduce uncomfortable side effects.
These functional fibers added to low-fiber foods do offer health benefits. However, a diet with various fiber sources from different foods such as fruits, vegetables, whole grains, nuts, seeds, legumes, and beans is the best way to help individuals meet their needs for daily fiber intake. Fiber from whole foods offers additional health benefits from vitamins, minerals, and phytochemicals than when it is an added ingredient to produced foods.
Fiber and the nutrition facts panel. When the math isn’t mathing!
The guidelines for nutrition facts on food products have changed in the last several years. One change included how fiber is listed on the label, with manufacturers being able to remove fibers considered indigestible from the “Net Carbohydrate” per serving and the total calories. “Net Carbohydrate" are the carbohydrates left when you subtract “Dietary Fiber” from “Total Carbohydrate.“ This is where nutrition facts panels can be confusing for some.
To better understand how the total for carbohydrates is determined, it’s important to know that not all information is listed, and some information is essentially listed twice.
On the nutrition facts panel, the grams of “Dietary Fiber” listed under “Total Carbohydrate” are included in the total grams of carbohydrates. The same applies to “Total Sugars”; they are included in the “Total Carbohydrate” count. The “Includes Added Sugar” is part of the “Total Sugars” count.
So, in the example here, the 4 grams of “Total Sugars” include the 2 grams of “Added Sugars”. Only 4 grams of sugar is included in the “Total Carbohydrate”.
The difference between the grams of “Total Carbohydrate” listed and the total of “Dietary Fiber” and “Total Sugars” included in the “Total Carbohydrate” total is the remaining various forms of complex carbohydrates commonly referred to as starch.
Now for the mathing…
On the nutrition facts example above, the "Total Carbohydrate” is 46 grams.
To find the grams of complex carbohydrate per serving:
46 grams Total Carbohydrate
-7 grams Dietary fiber
- 4 grams Total Sugar.
35 grams of Complex Carbohydrates
What about “Net Carbohydrate” on a package? Many labels now include “Net Carbs," which is the remaining of "Total Carbohydrate" minus "Dietary Fiber."
The Net Carbs in the Nutrition Label above would be:
46 grams Total Carbohydrate
– 7 grams Dietary Fibers
39 grams Net Carbohydrates
The Net Carbohydrates are important to understand because the “Calories” on the nutrition facts panel do not always add up if you only look at the "Total Carbohydrates,” "Total Fat,” and "Protein."
On all food labels, “Calories” are based on adding the total calories from the fat, protein, and carbohydrates (some of them) content. Fat provides 9 calories per gram, while protein and carbohydrates provide 4 calories per gram.
Has anyone else ever spent far too long trying to figure out how the calories listed are less than what the combined total of fat, carbs, and protein should be on a label?
Labeling laws do not require all calories from “Dietary Fiber” or "Sugar Alcohols" to be included in the “Calories.”
In the nutrition label example, if we counted all the calories from the "Total Carbohydrate,” the “Calories” would be 264 per serving. However, only the "Net Carbs" and some dietary fiber are counted in the "Calories." A few soluble fiber types have a caloric value of 1 kcal/gram, while most soluble and insoluble have no caloric value. This is why only 240 calories are listed per serving in the example. Unfortunately, this information is difficult to find and is not typically explained on the Nutrition Facts panel or food labels.
How much fiber is enough? Based on research, the total fiber requirement per day that offers protection against heart disease is approximately 25 grams for women and 38 grams for men (Dahl et al., 2015). According to FDA.gov, at least 28 g of dietary fiber must be consumed most days (preferably every day) on a diet of 2000kcals to meet 100 % of the Daily Values for fiber intake. The adequate fiber intake is about 14 g for every 1000 kcal (Dahl et al., 2015).
An easier way to ensure adequate fiber in your diet is to average 1 – 2 grams of fiber per 100 calories, depending on your caloric needs. For those who need less than the average 2000 calories a day, you will want to use a higher fiber-to-calorie ratio of at least 1.5 - 2 grams of fiber per 100 calories. Those who need more than 2000 calories daily only need 1-1.5 grams of fiber per 100 calories. Eating more fiber than recommended is not harmful to health, but additional health benefits may not exist. If you are not getting enough fiber, slowly increasing your fiber and water intake will reduce the chance of GI discomfort.
Ways to include fiber in your daily diet: You can get adequate fiber by eating various fruits, vegetables, legumes, beans, nuts, and seeds. Here is an example of foods you could incorporate to increase fiber in your diet:
Breakfast: Whole grain toast, scrambled egg, and blueberries with cottage cheese.
Lunch: Brown rice bowl with roasted chicken, vegetables, and beans + Mixed fruit bowl (honeydew with grapes).
Dinner: Turkey chili with black beans, pinto beans, carrots, and bell pepper over chickpea pasta. Watermelon and feta cheese salad.
Snack: Whole grain crackers, carrot sticks, and ricotta ranch dip.
A healthy diet can include food products that use added functional fibers marketed as high fiber with reduced “Net Carbs.” For example, swapping out higher-fat, low-fiber tortillas with high-fiber tortillas or using low-carbohydrate breads made with modified wheat starch may be beneficial for managing blood sugar levels and supporting gut health. Adding fortified high-fiber food is unnecessary if you already eat adequate fiber from whole foods.
Reference:
1. Is Dietary Fiber Considered an Essential Nutrient? Kohn, Jill Balla Journal of the Academy of Nutrition and Dietetics, Volume 116, Issue 2, 360
2. Qin, Y. Q., Wang, L. Y., Yang, X. Y., Xu, Y. J., Fan, G., Fan, Y. G., Ren, J. N., An, Q., & Li, X. (2023). Inulin: properties and health benefits. Food & function, 14(7), 2948–2968. https://doi.org/10.1039/d2fo01096h
3. Dietary Fiber and Health, edited by Susan Cho and Nelson Almeida, Taylor & Francis Group, 2012. ProQuest Ebook Central, https://ebookcentral.proquest.com/lib/ohsu/detail.action?docID=932837.
4. Clinic, C. (2024, August 12). What is the difference between soluble and insoluble fiber? Cleveland Clinic. https://health.clevelandclinic.org/whats-the-difference-between-soluble-and-insoluble-fiber
5. Sheng, W., Ji, G., & Zhang, L. (2023). Immunomodulatory effects of inulin and its intestinal metabolites. Frontiers in Immunology, 14, 1224092. https://doi.org/10.3389/fimmu.2023.1224092
6. Clinic, C. (2024b, August 12). What is the difference between soluble and insoluble fiber? Cleveland Clinic. https://health.clevelandclinic.org/whats-the-difference-between-soluble-and-insoluble-fiber
7. Current Dietary Guidelines | Dietary Guidelines for Americans. (n.d.). https://www.dietaryguidelines.gov/current-dietary-guidelines
8. How to add more fiber to your diet. (n.d.). Mayo Clinic. https://www.mayoclinic.org/healthy-lifestyle/nutrition-and-healthy-eating/in-depth/fiber/art-20043983
9. UCSF [UCSF Health]. (n.d.). Patient Education: Fiber Supplements. Patient Education: Fiber Supplements. https://www.ucsfhealth.org/education/fiber-supplements
10. Position of the Academy of Nutrition and Dietetics: Health Implications of Dietary Fiber Dahl, Wendy J. et al. Journal of the Academy of Nutrition and Dietetics, Volume 115, Issue 11, 1861 – 1870
11. FDA.gov [fda.gov] . Interactive Nutrition Facts Label-Dietary Fiber. accessdata.fda.gov. https://www.accessdata.fda.gov/scripts/interactivenutritionfactslabel/assets/InteractiveNFL_DietaryFiber_October2021.pdf
12. FDA. (n.d.). How to Understand and Use the Nutrition Facts Label. The Nutrition Facts Label. https://www.fda.gov/food/nutrition-facts-label/how-understand-and-use-nutrition-facts-label
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