Fiber is a hot topic, and for good reason! Dietary fiber is a star when it comes to alleviating constipation and diarrhea, improving metabolic health, feeding the helpful microbes that inhabit our gut, and protecting cardiovascular health. With all this positive press directed towards dietary fiber, many companies are producing and marking fiber supplements with a multitude of health claims. So how do you know if you get enough fiber each day, and if a fiber supplement is right for you?
Fibers are carbohydrate components of plant foods that our bodies cannot digest on their own. Instead of being digested in the small intestine, fiber is either fermented (broken down) by gut microbes or passes through the GI tract largely intact. Having enough fiber in our diet is one way to keep these microbes healthy and abundant, providing balance to the ecosystem that lives within us. When our gut microbiome is thriving, we experience improved digestion and nutrient absorption, immunity, and better mental health through the gut-brain axis.
There are many different types of fiber that interact with our digestive tract and microbiome in a variety of ways. Broadly, fiber is classified as soluble or insoluble. Soluble fiber dissolves in water and forms a gel, while insoluble fiber does not dissolve in water. We can break it down even further:
Viscous (gel-forming) fibers:
- These soluble fibers absorb water and form a gel-like substance.
- What they do:
- Slow digestion and gastric emptying
- Help regulate blood sugar and cholesterol
- Can normalize stool (help both constipation and diarrhea)
- Examples: psyllium, beta-glucan, partially hydrolyzed guar gum (PHGG)
Fermentable (prebiotic) fibers:
- These are broken down by gut bacteria.
- What they do:
- Feed beneficial microbes (prebiotic effect)
- Produce short-chain fatty acids (SCFAs) that support gut and metabolic health
- Can cause gas/bloating in some people, especially those with IBS
- Examples: inulin, fructooligosaccharides (FOS), resistant starch
Non-viscous (bulking) fibers:
- These add bulk and speed transit through the GI tract.
- What they do:
- Helpful for constipation (increasing stool mass)
- Less impact on cholesterol or glycemic control
- Examples: wheat bran, cellulose
We can see that not all fiber works the same way, and that selecting the incorrect type of fiber may actually worsen symptoms rather than make an improvement. It is also important to be aware of how much fiber our body needs. Increasing fiber too quickly can worsen bloating, gas, or discomfort, so gradual increases of 2-3 grams/day paired with adequate fluid intake are key.
General recommendations are about 25 grams/day for women and about 38 grams/day for men. A more specific way to calculate fiber needs is about 14 grams of fiber per 1,000 calories eaten in a day. Based on data from the National Health and Nutrition Examination Survey, most people fall well short of these targets. A dietitian can use this information to help you calculate your specific fiber needs and provide recommendations for the type of fiber that is most appropriate for you.
The most important takeaway is that food sources of fiber are always preferred to supplements! Fiber-rich foods provide more than just fiber—they also contain vitamins, minerals, antioxidants, and a variety of fiber types working together. Whole foods provide a diversity of fibers, which supports a more diverse and resilient gut microbiome—something a single isolated supplement can’t replicate. While fiber supplements can be helpful in some situations, we always work to increase fiber from food sources first.
Here are some high-fiber foods to emphasize:
- Fruits with skin or seeds (berries, kiwi – with skin!, pears, apples)
- Vegetables (leafy greens, carrots, squash)
- Legumes (lentils, chickpeas, black beans)
- Whole grains (oats, quinoa, brown rice)
- Nuts and seeds (soaked chia, flax, almonds)
And, some easy ways to increase fiber from food:
- Add chia or flax to yogurt, oatmeal, or smoothies
- Swap refined grains for whole grains
- Include a fruit or vegetable at most meals/snacks
- Use beans or lentils in soups, salads, or pasta dishes (canned beans and lentils are great no-prep add ons!)
You might be wondering, when is a fiber supplement appropriate? We may recommend our patients use a fiber supplement when fiber intake is consistently below needs despite dietary changes or during temporary situations, such as post-surgery, travel, or illness. Gastrointestinal symptoms can also play a role, so when we are working to manage symptoms such as constipation or diarrhea, targeting a specific type of fiber may be needed. Fiber supplements can also be a great tool when barriers such as low appetite or poor chewing ability are present, or when access to higher-fiber foods is limited.
When it comes to fiber supplements, unless recommended by a healthcare provider, avoid the hype and focus on fiber-rich plant foods first. If you are unsure how much fiber you eat in a day, how much your body needs, or feel a fiber supplement might be right for you, reach out to a dietitian or your doctor for more guidance.
References:
Aune, D., Chan, D. S. M., Lau, R., Vieira, R., Greenwood, D. C., Kampman, E., & Norat, T. (2011). Dietary fibre, whole grains, and risk of colorectal cancer: Systematic review and dose–response meta-analysis of prospective studies. BMJ, 343, d6617. https://doi.org/10.1136/bmj.d6617
Barber, T. M., Kabisch, S., Pfeiffer, A. F. H., & Weickert, M. O. (2020). The health benefits of dietary fibre. Nutrients, 12(10), 3209. https://doi.org/10.3390/nu12103209
Gibson, G. R., Hutkins, R., Sanders, M. E., et al. (2017). The ISAPP consensus statement on the definition and scope of prebiotics. Nature Reviews Gastroenterology & Hepatology, 14(8), 491–502. https://doi.org/10.1038/nrgastro.2017.75
Makki, K., Deehan, E. C., Walter, J., & Bäckhed, F. (2018). The impact of dietary fiber on gut microbiota in host health and disease. Cell Host & Microbe, 23(6), 705–715. https://doi.org/10.1016/j.chom.2018.05.012
McRorie, J. W., Jr, & McKeown, N. M. (2017). Understanding the physics of functional fibers in the gastrointestinal tract: an evidence-based approach to resolving enduring misconceptions about insoluble and soluble fiber. Journal of the Academy of Nutrition and Dietetics, 117(2), 251–264. https://doi.org/10.1016/j.jand.2016.09.021
Reynolds, A., Mann, J., Cummings, J., et al. (2019). Carbohydrate quality and human health: Systematic reviews and meta-analyses. The Lancet, 393(10170), 434–445. https://doi.org/10.1016/S0140-6736(18)31809-9
U.S. Department of Agriculture & U.S. Department of Health and Human Services. (2020). Dietary Guidelines for Americans, 2020–2025. https://www.dietaryguidelines.gov/
