Dietary fiber is the part of plant foods that our bodies canât digest. Unlike other nutrients that are broken down and absorbed, fiber passes through the digestive system relatively intact. You can find fiber in a variety of plant-based foods such as fruits, vegetables, legumes, seeds, and whole grains. Many high-fiber plant foods contain both soluble and insoluble fiber. Although all prebiotics are fiber, not all fiber is a prebiotic. So, what exactly qualifies certain fibers as prebiotics?
What Are the Classifications for a Prebiotic?
For a fiber to be considered a prebiotic, it must meet specific criteria:
- Resists gastric acidity, enzymatic hydrolysis, and absorption in the GI tract
- Fermented by the intestinal microflora
- Stimulates the growth and/or activity or intestinal bacteria
Now that we understand what prebiotics are, lets break down the two types of dietary fiber you’ll most commonly encounter: soluble and insoluble.
Soluble vs. Insoluble Fiber: Whatâs the Difference?
There are two main types of fiberâsoluble and insolubleâand both play important roles in digestive health.
- Soluble fiber dissolves in water and forms a gel-like substance in the gut. Itâs typically fermented by the beneficial bacteria in your colon. Foods rich in soluble fiber include oats, barley, legumes (like beans and peas), fruits (such as apples and citrus), carrots, broccoli, and root vegetables.
- Insoluble fiber doesnât dissolve in water and is not usually fermented by gut bacteria. Instead, it adds bulk to the stool, helping to keep bowel movements regular. Sources include the skins of fruits and vegetables, whole grains, potatoes, corn bran, leafy greens, and seeds. Insoluble fiber components like cellulose, hemicellulose, and lignin can be found in foods such as tomatoes, kiwi, whole grains, and nuts.
Understanding the types of fiber is important – but how much do we really need?
How Much Fiber Do We Actually NeedâAnd Are We Getting Enough?
The general daily fiber recommendations are:
- Women: 25 grams
- Men: 38 grams
Despite these guidelines, many individuals fall short. In recent decades, the rise of ultra-processed foods in Western diets has drastically reduced the amount of fiber people consume on a regular basis. In fact, studies show that average fiber intake in the U.S. and Europe falls about 30% below the recommended levels, leaving many of us missing out on the important health benefits fiber has to offer.
So, why is fiber so important? Let’s take a look at the many ways a fiber-rich diet can benefit your health?
What are the health benefits of a high-fiber diet?
Adding more fiber to your meals can offer a wide range of health benefits:
- Promotes regular bowel movements â Insoluble fiber helps absorb water and adds bulk to stool, making it easier to pass and preventing constipation or loose stools.
- Supports colon health â A fiber-rich diet may reduce the risk of developing diverticular disease, lessen symptoms of hemorrhoids, and lower the risk of colorectal cancer.
- Lowers cholesterol levels â Soluble fiber binds to cholesterol in the small intestine, reducing absorption and helping to lower blood cholesterol.
- Stabilizes blood sugar levels â By slowing the digestion and absorption of carbohydrates, soluble fiber helps regulate post-meal blood glucose and insulin levels. It also helps prolong the feeling of fullness by delaying gastric emptying.
- Aids in weight management â High-fiber diets are linked to lower body weight, reduced BMI, and decreased body fat thanks to increased satiety and better blood sugar control.
- Reduces risk of chronic diseases â Regular fiber intake is associated with a lower risk of type 2 diabetes, heart disease, and stroke. It may also contribute to a stronger immune system.
Fiber plays a vital role in maintaining overall health, but how can you increase your intake in a way that your body can tolerate?
How to incorporate more fiber into your diet â slowly increasing might by beneficial
While high-fiber foods and a high-fiber diet are great for your health, it may take some time to adjust. Suddenly incorporating a variety of high-fiber foods may lead to stomach cramping, bloating, and gas. It may be best to slowly add more high fiber foods over a few weeks. This will allow natural bacteria in your digestive system to adjust.
Make sure to stay hydrated when incorporating higher amounts of fiber. Fiber functions at its best when it absorbs water, allowing for stools to pass more easily. You can read more gut health blog tips here!Â
References
Akbar, A., & Shreenath, A. P. (2025). High Fiber Diet. In StatPearls. StatPearls Publishing. http://www.ncbi.nlm.nih.gov/books/NBK559033/
Barber, T. M., Kabisch, S., Pfeiffer, A. F. H., & Weickert, M. O. (2020). The Health Benefits of Dietary Fibre. Nutrients, 12(10), Article 10. https://doi.org/10.3390/nu12103209
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), 1861â1870. https://doi.org/10.1016/j.jand.2015.09.003
Fu, J., Zheng, Y., Gao, Y., & Xu, W. (2022). Dietary Fiber Intake and Gut Microbiota in Human Health. Microorganisms, 10(12), 2507. https://doi.org/10.3390/microorganisms10122507
Koh, A., De Vadder, F., Kovatcheva-Datchary, P., & Bäckhed, F. (2016). From Dietary Fiber to Host Physiology: Short-Chain Fatty Acids as Key Bacterial Metabolites. Cell, 165(6), 1332â1345. https://doi.org/10.1016/j.cell.2016.05.041
Slavin, J. L. (2008). Position of the American Dietetic Association: Health implications of dietary fiber. Journal of the American Dietetic Association, 108(10), 1716â1731. https://doi.org/10.1016/j.jada.2008.08.007
