By now, you're probably no stranger to fiber for gut health. After all, fiber plays a key role in gut health and digestion. What you might not be as familiar with is prebiotic fiber, which serves as a fuel source for your gut microbes and is essential for a healthy microbiome (the community of trillions of microbes living in your gut).
With rates of colorectal cancer on the rise in people under 50, researchers are starting to investigate not only the link between fiber and colon health, but also between the gut microbiome and colorectal cancer. This article will explore how fiber supports gut bacteria and emerging research on the connection between fiber, the gut microbiome, and colorectal cancer.
What Is the Gut Microbiome and Why Does It Matter?
The gut microbiome is the diverse community of bacteria, fungi, viruses, and other microbes that live in your large intestine. Your personal gut microbiome is as unique as a fingerprint. While it is difficult to define exactly what a "healthy" microbiome looks like, a diverse microbiome is a key marker of a healthy gut, and less diverse microbiota are associated with several inflammatory diseases.1
You can think of the microbiome like a vegetable garden. If you eat only one type of vegetable, your body may not be getting the diverse range of nutrients it needs to function optimally. But if you eat a range of different vegetables, you provide your body with a wide range of nutrients that promote health.
The same can be said of the microbiome. Different microbes have different roles and produce different metabolic byproducts (and in some cases, certain vitamins), so having a diverse community of microbes ensures that your body is getting a range of beneficial nutrients and byproducts.
How Does Fiber Support a Healthy Microbiome?
Eating enough fiber from diverse sources is critical for overall gut microbiome health. In particular, prebiotic fiber, which resists digestion in the small intestine and instead reaches the colon intact, is an important fuel source for your gut microbiome.
But while eating enough fiber is one part of the equation, it's equally important to eat a wide variety of foods high in fiber because different foods provide different types of fiber.
Two types of fiber are soluble and insoluble fiber. Soluble fiber dissolves in water, forming a gel-like substance that slows digestion, stabilizes blood sugar, and lowers cholesterol levels. Insoluble fiber does not dissolve; instead, it remains intact as it travels through the digestive tract. Insoluble fiber mechanically stimulates the gut, acting like a broom to sweep food and waste through your digestive tract and keep your bowel movements regular.2
Soluble fiber act as prebiotics, whereas insoluble fiber does not. That doesn't mean insoluble fiber isn't important—it is—but when it comes to feeding your gut microbes, soluble fiber is the clear winner.
When soluble fiber reaches your colon, it gets fermented by your gut bacteria. This produces metabolic byproducts, such as short-chain fatty acids (SCFAs). SCFAs, especially butyrate, help support a strong intestinal lining and gut barrier, and have been linked with lower levels of inflammation in the body.3
Our microbiome is made up of trillions of microbes, each needing unique fuel sources. This highlights the importance of not only eating enough fiber but also eating a variety of fiber types.4 Eating a variety of different high-fiber foods, including beans and legumes, oats, berries, apples, leafy greens, whole grains, nuts, and seeds, ensures you're giving your body enough diverse fibers to fuel all the different microbes in your gut.
One strategy I like to use with clients is encouraging them to eat 30 different plant foods each week. This helps ensure you're getting both enough fiber overall while also getting the variety your gut microbiome needs to thrive.
Why Are Experts Concerned About Rising Rates of Colon Cancer in Younger Adults?
Early-onset colorectal cancer is defined as colorectal cancer diagnosed in people under 50.5 Research shows that while the incidence of colorectal cancer has decreased in older adults, rates in adults under 50 in the United States have nearly doubled since the early 1990s.6
While there are likely many contributing factors to this rise in cases, the link between colorectal cancer, diet, and microbiome health is an active area of research. Scientists are investigating how dietary patterns, obesity, lifestyle factors, and microbiome changes may be contributing to the rise in cases of early-onset colorectal cancer.
What Does Emerging Research Say About the Microbiome and Colon Health?
It's thought that the microbial species that make up your own unique microbiome play a critical role in shaping the physical and chemical environment of your gut. For example, beneficial microbes ferment prebiotic fibers to produce the SCFAs needed to nourish your colon cells and maintain a strong gut barrier.
In contrast, when there's an imbalance or disruption to your microbiome (known as "dysbiosis"), there may be more harmful microbes than beneficial microbes. These microbes may produce harmful metabolites that increase inflammation, weaken the gut lining, or create an environment that makes your colon cells more vulnerable to damage.
However, while initial research suggests a relationship between the microbiome and colon health, this field continues to evolve, with researchers actively working to understand this complex relationship and its relation to rising rates of early-onset colorectal cancer. Studies are investigating the unique microbial communities in tumors from younger patients, as well as specific alterations in their baseline microbiome, to identify potential microbial markers associated with early-onset colorectal cancer.7,8
Key Takeaway
Keeping your microbiome healthy starts with a consistent, fiber-rich diet that includes a wide variety of high-fiber foods to support beneficial gut bacteria. Increasing your fiber intake by choosing more plant-based foods and using a fiber supplement when needed are evidence-based strategies for supporting digestive health, microbial diversity, and overall colon wellness.
And remember—you don't need to overhaul your diet all at once. Small, sustainable changes like switching to whole grains or adding legumes to your meals can make a big difference. These small shifts add up over time.
Support Your Daily Fiber Intake
Most Americans consume less fiber than recommended, making it challenging to fully support microbiome health through diet alone.
Doctor's Best gut health products, like Sunfiber Prebiotic Powder and Postbiotic Butyrate Capsules, can help complement a balanced diet and provide additional support for digestive health and healthy gut bacteria.
FAQs
How much fiber should adults consume each day?
Most adults should aim for approximately 25–38 grams of fiber daily, depending on age and sex.
What does fiber do for the gut microbiome?
Fiber serves as food for beneficial gut microbes, helping them produce compounds that support digestive and colon health.
What are the best foods for a healthy microbiome?
Fiber-rich foods such as fruits, vegetables, legumes, whole grains, nuts, and seeds help nourish beneficial gut bacteria.
Is there a connection between the microbiome and colorectal cancer?
Researchers are actively studying how changes in the gut microbiome may influence colorectal cancer risk, though more research is needed to understand the relationship.
Can a fiber supplement help increase daily fiber intake?
Yes. Fiber supplements can help fill dietary gaps and support digestive health when used alongside a balanced, fiber-rich diet.
References
- Pickard, J. M., Zeng, M. Y., Caruso, R., & Núñez, G. (2017). Gut microbiota: Role in pathogen colonization, immune responses, and inflammatory disease. Immunological Reviews, 279(1), 70-89. https://doi.org/10.1111/imr.12567
- Ariyarathna, P., Mizera, P., Walkowiak, J., & Dziedzic, K. (2025). Physicochemical and Functional Properties of Soluble and Insoluble Dietary Fibers in Whole Grains and Their Health Benefits. Foods, 14(14), 2447. https://doi.org/10.3390/foods14142447
- Cong, J., Zhou, P., & Zhang, R. (2022). Intestinal Microbiota-Derived Short Chain Fatty Acids in Host Health and Disease. Nutrients
- Vinelli, V., Biscotti, P., Martini, D., Marino, M., Meroño, T., Nikoloudaki, O., Calabrese, F. M., Turroni, S., Taverniti, V., Caballero, A. U., Andrés-Lacueva, C., Porrini, M., Gobbetti, M., Angelis, M. D., Brigidi, P., Pinart, M., Nimptsch, K., Guglielmetti, S., & Riso, P. (2022). Effects of Dietary Fibers on Short-Chain Fatty Acids and Gut Microbiota Composition in Healthy Adults: A Systematic Review. Nutrients, 14(13), 2559. https://doi.org/10.3390/nu14132559, 14(9), 1977. https://doi.org/10.3390/nu14091977
- Barot, S. V., Sangwan, N., Nair, K. G., Schmit, S. L., Xiang, S., Kamath, S., Liska, D., & Khorana, A. A. (2024). Distinct intratumoral microbiome of young-onset and average-onset colorectal cancer. EBioMedicine, 100, 104980. https://doi.org/10.1016/j.ebiom.2024.104980
- Dharwadkar, P., Zaki, T. A., & Murphy, C. C. (2022). Colorectal cancer in younger adults. Hematology/Oncology Clinics of North America, 36(3), 449. https://doi.org/10.1016/j.hoc.2022.02.005
- Barot, S. V., Sangwan, N., Nair, K. G., Schmit, S. L., Xiang, S., Kamath, S., Liska, D., & Khorana, A. A. (2024). Distinct intratumoral microbiome of young-onset and average-onset colorectal cancer. EBioMedicine, 100, 104980. https://doi.org/10.1016/j.ebiom.2024.104980
- Yang, Y., Du, L., Shi, D., Kong, C., Liu, J., Liu, G., Li, X., & Ma, Y. (2021). Dysbiosis of human gut microbiome in young-onset colorectal cancer. Nature Communications, 12, 6757. https://doi.org/10.1038/s41467-021-27112-y
About the Author
Sarah is a registered dietitian specializing in gut health. With over eight years of experience in the health and wellness industry, she combines clinical expertise with lived experience with gut health issues to inform everything she writes. Her goal as a writer is to ensure that complex health information is simplified without losing context so people can make informed decisions about their health. She currently lives in British Columbia, Canada, where she enjoys lifting weights, reading sci-fi/fantasy books, and crocheting in the company of her husband and two cats.