Nutrition

Soluble vs. Insoluble Fiber: What's The Difference?

5 min read
Not all fiber is created equal—they each have unique benefits.
Not all fiber is created equal—they each have unique benefits.

Article Content

How much do you know about fiber? While many recognize that fiber is an important part of a healthy diet, fewer are clear on the specifics—like the difference between soluble fiber and insoluble fiber, for example, or the amount of fiber that should be consumed daily. This is where knowledge really comes in handy: By having an awareness of the facts, you’re arming yourself with the information and tools needed to create a habit that sticks—whether the goal is to make better food choices, break a sweat more often, or just remember to take your multivitamins.

When it comes to the science, there’s no two ways about it: Fiber provides several health benefits and consuming enough of it is important for supporting intake needs of this essential macronutrient. Here’s the catch, though: Despite all evidence pointing to the value and importance of getting enough fiber, most people in the United States aren’t coming anywhere near the recommended levels of daily fiber intake—despite believing otherwise. Recent data reveals that only about 6 percent (yep, you read that right) of the U.S. adult population ages 19-50 meets current recommendations.* (1, 8)

Translation? The fiber intake gap is real. And the first step to bridging it (and consequently reaping the benefits), is to get informed. Here, we break down the two different types of dietary fiber—soluble fiber and insoluble fiber—their unique benefits, and some foods to incorporate from each group. Let’s get down to business!

Fiber 101: Soluble vs. insoluble fiber

Before we dive into the different types of fiber, let’s cover the basics first, starting with fiber itself. Dietary fiber refers to the indigestible part of plant material—that is, the part of plant-based food that passes through the digestive system mostly intact, meaning that it cannot be easily digested, especially in the small intestine. (10)

Dietary fiber is often divided into two groups: Soluble fiber and insoluble fiber. Though they offer different benefits, one thing is clear—they’re both important for supporting digestive health. Soluble fiber dissolves in water and transforms into a gel-like substance during digestion. “Soluble fiber slows the movement of food through the digestive system and helps prevent certain fats and/or sugars from being broken down and absorbed,” explains Dr. Mastaneh Sharafi, PhD, a registered dietitian and Ritual’s VP of Scientific Affairs. (It’s also present in psyllium, which is commonly used as a fiber supplement.) Insoluble fiber, on the other hand, does not dissolve in water. “Rather, it draws water, promoting the movement of materials through the digestive tract, resulting in an increased stool bulk,” says Dr. Mastaneh.* (11, 12)

To keep it simple: Soluble fiber dissolves in water, and is shown to help slow digestion and increase the bioavailability of some minerals, while insoluble fiber does not dissolve in water, and is therefore left intact as food moves through the gastrointestinal tract, promoting digestive health. And eating a high-fiber diet—or at the very least, making an effort to include fiber-rich foods on the plate—can help support digestive health.* (9)

What foods to seek out

The not-so-great news is that many of us are falling short on fiber requirements. (The Academy of Nutrition and Dietetics recommends that adult women† aim to eat around 25 grams of fiber per day, while adult men aim for around 38 grams.) Fortunately, there are many sources of both soluble and insoluble fibers, with the majority of plant foods containing some of each—another reason to load up on a variety of colorful produce. (7)

Sources of soluble fiber include legumes (like lentils and dried beans), guar gum seeds, oats, oat bran, barley, citrus fruits, apples, carrots, and peas. Sources of insoluble fiber include wheat bran, whole grains (whole wheat flour counts, too), brown rice, nuts, seeds (think chia seeds and flaxseeds), green beans, celery, cauliflower, potatoes, and the skins of many fruits and vegetables. (Need some more inspo? Here’s a list of 21 high-fiber foods to explore—all are good sources for upping intake.)

What about fiber supplements?

They’re worth considering depending on life stage, specific needs, and typical dietary intake. While we recommend a food-first approach to nutrition—that is, aiming to meet nutrient needs through a balanced diet of carbohydrates, protein, and healthy fats—a fiber supplement can certainly be a helpful addition to a routine, especially if someone struggles with eating fibrous whole foods (whole grains, veggies, fruits, legumes, and nuts) on a regular basis. Studies show that fiber supplements can help shore up intake and support the health effects of dietary fiber, providing many of the same benefits as their food counterparts. (Just remember that supplements are intended to be just that: supplements to a healthy lifestyle, rather than a substitute for good choices.)* (1)

The essential takeaway

Fiber has health benefits, and many of us are coming up short. Dr. Mastaneh suggests keeping it simple: “When it comes to fiber, instead of focusing on specific types, we should be aiming to get enough overall.” We suggest making it a habit to eat a balanced, fiber-rich diet full of whole grains, vegetables, and fruits—and incorporating a fiber supplement if and when extra support is needed.*

References:

  1. James W Anderson, Pat Baird, Richard H Davis, Jr, Stefanie Ferreri, Mary Knudtson, Ashraf Koraym, Valerie Waters, Christine L Williams, Health benefits of dietary fiber, Nutrition Reviews, Volume 67, Issue 4, 1 April 2009, Pages 188–205.
  2. Quagliani, D., & Felt-Gunderson, P. (2016). Closing America's Fiber Intake Gap: Communication Strategies From a Food and Fiber Summit. American journal of lifestyle medicine, 11(1), 80–85.
  3. Barber, T. M., Kabisch, S., Pfeiffer, A., & Weickert, M. O. (2020). The Health Benefits of Dietary Fibre. Nutrients, 12(10), 3209. https://doi.org/10.3390/nu12103209
  4. Kay R. M. (1982). Dietary fiber. Journal of lipid research, 23(2), 221–242.
  5. Holscher H. D. (2017). Dietary fiber and prebiotics and the gastrointestinal microbiota. Gut microbes, 8(2), 172–184.
  6. El-Salhy, M., Ystad, S. O., Mazzawi, T., & Gundersen, D. (2017). Dietary fiber.. (Review). International journal of molecular medicine, 40(3), 607–613.
  7. Dahl, W. J., & Stewart, M. L. (2015). Position of the Academy of Nutrition and Dietetics: Health Implications of Dietary Fiber. Journal of the Academy of Nutrition and Dietetics, 115(11), 1861–1870.
  8. USDA, Agricultural Research Service. Usual Nutrient Intake from Food and Beverages, by Gender and Age, What We Eat in America, NHANES 2015-2018. 2021.
  9. Dahl, W. J., & Stewart, M. L. (2015). Position of the Academy of Nutrition and Dietetics: Health Implications of Dietary Fiber. Journal of the Academy of Nutrition and Dietetics, 115(11), 1861–1870.
  10. Mayo Clinic. Nutrition and Healthy Eating. Dietary fiber: Essential for a healthy diet. Last updated Jan. 6, 2021. Accessed June 22, 2021.
  11. Chutkan, R.; et al. Viscous versus nonviscous soluble fiber supplements: Mechanisms and evidence for fiber-specific health benefits. J Am Acad Nurse Pract. 2012, 24(8):476-87. (Abstract)
  12. U.S. Department of Health and Human Services, Food and Drug Administration (FDA). Interactive Nutrition Facts Label. Dietary Fiber Fact Sheet. March 2020.

Share

Meet Our Experts

This article features advice and has been reviewed by members of our Science Team.

Science Thumb — Mastaneh

Dr. Mastaneh Sharafi, PhD, RD, VP of Scientific Affairs

Dr. Mastaneh Sharafi has a PhD in Nutritional Sciences and is a Registered Dietitian. She received her training from Penn State University and University of Connecticut where she researched dietary patterns, chemosensory perception and community nutrition. Her dietetic work is focused on promoting healthy eating habits by translating the science of nutrition into practical information for the public.

Science Thumb — Mastaneh

Dr. Mastaneh Sharafi, PhD, RD, VP of Scientific Affairs

Dr. Mastaneh Sharafi has a PhD in Nutritional Sciences and is a Registered Dietitian. She received her training from Penn State University and University of Connecticut where she researched dietary patterns, chemosensory perception and community nutrition. Her dietetic work is focused on promoting healthy eating habits by translating the science of nutrition into practical information for the public.

Shop Multivitamin

Multivitamin

Shop Protein
New

Protein

Shop Pregnancy

Pregnancy

Shop Bundles

Bundles