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Unpacking Dietary and Supplemental Fiber: When to Take Fiber Supplements

Benefits of Fiber and the Difference Between Food and Supplements

Key Takeaways
  • Eating foods rich in fiber is the most beneficial way to add fiber into your diet.
  • Supplemental fiber is a late-stage intervention to try after a standard GI protocol (including diet and probiotics).
  • If you’re on a special diet like keto, low FODMAP, or SCD, you may need supplemental fiber.

Fiber supplements might seem like a simple addition to your diet to help move things along, but they have the potential to tax your digestive system unnecessarily if they aren’t used strategically. 

In our clinic at the Ruscio Institute for Functional Medicine, we always recommend that our patients take fiber supplements only after implementing a comprehensive gut protocol, which includes probiotics, dietary changes, and other foundational approaches.

If you skip a more holistic approach and go straight to fiber supplements, you could be putting your digestive system under stress. That’s because introducing a fiber supplement to an already struggling system can further irritate and inflame the bowels, resulting in potential side effects like diarrhea, constipation, cramping, bloating, and nausea [1, 2].

Roughly 95% of Americans fail to eat the recommended amount of fiber each day [3]. The Mayo Clinic recommends that women aim for 21-25 grams of fiber per day and men shoot for 30-38 grams [4]. That being said, dietary guidelines around how much fiber is too much fiber aren‘t consistent across individuals. Your own health status (especially gut health) will greatly determine how much fiber you can tolerate in a meal or in a day.

Unpacking Dietary and Supplemental Fiber: When to Take Fiber Supplements - high%20fiber%20foods Landscape L

Eating more fiber-rich foods (like fruits, veggies, seeds, and whole grains) as part of an overall healthy diet is a far more preferable way to increase your total fiber intake. The health benefits of eating fiber-rich food far outweigh those of simply taking a dose of Metamucil, and in fact, some studies show very little clinical benefit of taking fiber supplements when compared to a high-fiber diet [5, 6, 7, 8].

All this said, there are certain instances in which it would make sense to take supplemental fiber. Those who have been following special diets like low FODMAP, keto, or the SCD (specific carbohydrate diet) and aren‘t feeling great may benefit from adding in some fiber, for example. 

Let’s go over when to take fiber supplements, the potential benefits and risks, and some of the best options if supplementing is, in fact, the right course of action for you.

When to Take Fiber Supplements

Fiber should generally be a later-stage intervention for most patients. Sometimes a well-meaning GI doctor will recommend fiber to a patient experiencing constipation or diarrhea, only for the patient’s symptoms to get worse over time. That’s because, as a rule, fiber supplements aren’t going to address the root cause of gut challenges.

It’s important to start out with the fundamentals when it comes to gut healing. For most people, this means an anti-inflammatory diet, and often probiotics and/or digestive enzymes. Next, a few more specialized gut-healing supplements such as L-glutamine, zinc, and/or vitamin D may come into play. It’s only after this fundamental approach fails to yield positive results that we consider fiber supplements.

Keep in mind that when to take fiber supplements can be as important as which supplements you take. Supplemental fiber can certainly be helpful for some people, but introducing it at the wrong time can be hard on your gut and may complicate the healing process. 

Fiber Supplements for Specialized Diets: Keto, Low FODMAP, and SCD

Special diets geared toward addressing gut challenges like SIBO (small intestinal bacterial overgrowth), IBS (irritable bowel syndrome), IBD (inflammatory bowel disease), or diverticulitis tend to lean away from carbs and toward proteins and fats. Although some of these diets do allow for adequate sources of dietary fiber, it’s easy to fall into a habit of not eating enough fiber when on these diets. 

Importantly, these ways of eating aren’t meant to be undertaken for the long-term. Rather, these diets should only be used for several days to achieve remission from an acute relapse or flare-up, at which point, dietary fiber should be slowly increased to recommended amounts, according to Belgian researchers [9].

The Ketogenic Diet

The ketogenic diet aims to replace most of the calories you’d generally take in from carbohydrates with calories from fat. And as a result of this swap, you’re likely dramatically reducing your total intake of high-fiber foods. While the keto diet has swept the internet with promises of dramatic weight loss and endless energy, the research doesn’t support this way of eating in the long-term, especially when it comes to cardiovascular health and digestive health.

A study done with women on the keto diet found that every participant experienced an increase in LDL cholesterol (the kind associated with heart disease) [10]. And a 2021 literature review looked at the effects of the keto diet on gut health and found that without a diet rich in fiber, gut microbes pulled carbon from the gut lining, resulting in increased gut permeability over time [11]. Gut permeability (aka leaky gut) is associated with poor immunity, inflammatory diseases, and a host of other systemic problems.

If you’re on the ketogenic diet and are having diarrhea or difficulty with bowel movements, you could benefit from fiber supplements. But talk to your healthcare provider to find out how long you can safely stay on this diet and when it’s appropriate to add fiber-rich foods back into your diet.

Low FODMAP and Specific Carbohydrate Diet (SCD)

The benefits of supplemental fiber also extend to those on the low FODMAP diet and the specific carbohydrate diet (SCD) [12]. Both of these diets are designed to limit very specific types of fiber (often prebiotic fiber) for a period of time to reduce inflammation, kill harmful bacteria, and allow your digestive tract to heal. 

In the case of the low FODMAP diet, you’re generally trying to starve out bacteria living in your small intestine by limiting the fiber those bacteria like to eat. 

In the case of SCD, this diet was designed specifically for celiac patients to help them avoid gluten and other irritants found in cereal grains, and other fibers found in starchy vegetables and fructooligosaccharides [13].

Again, these ways of eating are meant to be temporary diets, not lifestyle diets. They’re designed to address a specific issue that may require a temporary reduction in dietary fiber intake. If one of these diets causes diarrhea or constipation, it’s a good time to take a fiber supplement.

Unpacking Dietary and Supplemental Fiber: When to Take Fiber Supplements - how%20to%20get%20more%20fiber%20with%20a%20sensitive%20gut Landscape L

The Best Fiber Supplements

Fiber, in general, is indigestible by the human digestive tract. One of the many (many, many) benefits of probiotics is their ability to digest and assimilate fibers that we as humans cannot. We benefit from this digestion, but the health benefits are far greater when the fiber comes from food, rather than supplements [14].

A wide swath of healthy plant-based foods contain fiber (fruit, vegetables, grains, legumes, nuts, seeds — especially omega 3-rich flax seeds and chia seeds), but if you’re in a position that prevents you from eating enough of these foods, functional (supplemental) fiber is the best approach. Functional fiber is made up of isolated carbohydrates that have been shown in clinical research to be beneficial to human physiology [8, 14].

If the answer to the question of when to take fiber supplements is “now,“ the best fiber to take is psyllium husks, a functional fiber that‘s been shown to improve cholesterol, lower blood sugar levels, and relieve constipation and diarrhea [6, 8, 14].

According to a 2017 comprehensive literature review, randomized controlled trials on fiber supplements have shown that psyllium husk (Metamucil) has a wider range of positive benefits for cholesterol, blood glucose, and stool regularity than other well-researched fiber supplements with health benefits, including large-particle wheat bran, guar gum, and beta-glucan from oats [14].

In contrast, some types of fiber supplements, including wheat dextrin (Benefiber), inulin (usually from chicory), and methylcellulose (Citrucel), have not shown any of these benefits [14].

Again, dietary fiber is the clear winner when it comes to the biggest health benefits of fiber. When consumed in high amounts, dietary fiber from the plant sources I listed above is largely associated with a reduced risk of stroke, heart attack, heart disease, and cancer, and has been shown to support colon health, gut health, heart health, healthy weight, and metabolic health [3, 6, 8, 14, 15, 16].

But if you‘re on a diet that restricts these foods, psyllium husks are a good supplemental option for the short-term, until you can begin adding some of these foods back into your diet.

Fiber Supplements: To Take or Not to Take, and When?

Fiber is decidedly more beneficial to your health if it’s sourced from whole foods in your healthy diet. While the amount of fiber you eat each day is individual to your own health needs, a diet rich in dietary fiber is associated with improved cardiovascular health, digestive health, reduced cancer risk, improved blood pressure and blood sugar, and more.

If you’ve gone through the standard GI protocol of reducing inflammatory foods, plus adding in probiotics, enzymes, and other gut-supporting supplements, but aren’t seeing the results you’re looking for, it might be time to take fiber supplements.

Certain diets require a restriction of specific carbohydrates, which can have an impact on how much dietary fiber you‘re able to eat during the time you‘re on that diet. If you‘re feeling badly or experiencing diarrhea and/or constipation on a diet like the ketogenic diet, low FODMAP, or SCD, it’s a good idea to add in a functional supplemental fiber like psyllium husks, which is the main ingredient in Metamucil.

Navigating digestive challenges can be stressful and time-consuming. But we’re here to help. Head over to our patient portal to become a patient with us.

The Ruscio Institute has developed a range of high-quality formulations to help our patients and audience. If you’re interested in learning more about these products, please click here. Note that there are many other options available, and we encourage you to research which products may be right for you.

➕ References
  1. Nagarajan N, Morden A, Bischof D, King EA, Kosztowski M, Wick EC, et al. The role of fiber supplementation in the treatment of irritable bowel syndrome: a systematic review and meta-analysis. Eur J Gastroenterol Hepatol. 2015 Sep;27(9):1002–10. DOI: 10.1097/MEG.0000000000000425. PMID: 26148247.
  2. Christodoulides S, Dimidi E, Fragkos KC, Farmer AD, Whelan K, Scott SM. Systematic review with meta-analysis: effect of fibre supplementation on chronic idiopathic constipation in adults. Aliment Pharmacol Ther. 2016 Jul;44(2):103–16. DOI: 10.1111/apt.13662. PMID: 27170558.
  3. Quagliani D, Felt-Gunderson P. Closing america’s fiber intake gap: communication strategies from a food and fiber summit. Am J Lifestyle Med. 2017 Feb;11(1):80–5. DOI: 10.1177/1559827615588079. PMID: 30202317. PMCID: PMC6124841.
  4. High-fiber foods – Mayo Clinic [Internet]. Available from:
  5. Wagenaar CA, van de Put M, Bisschops M, Walrabenstein W, de Jonge CS, Herrema H, et al. The effect of dietary interventions on chronic inflammatory diseases in relation to the microbiome: A systematic review. Nutrients. 2021 Sep 15;13(9). DOI: 10.3390/nu13093208. PMID: 34579085. PMCID: PMC8464906.
  6. White N. A Guide to Recommending Fiber Supplements for Self-Care. Am J Lifestyle Med. 2020 Dec;14(6):589–91. DOI: 10.1177/1559827620947375. PMID: 33117099. PMCID: PMC7566180.
  7. Dahl WJ, Stewart ML. Position of the academy of nutrition and dietetics: health implications of dietary fiber. J Acad Nutr Diet. 2015 Nov;115(11):1861–70. DOI: 10.1016/j.jand.2015.09.003. PMID: 26514720.
  8. Lambeau KV, McRorie JW. Fiber supplements and clinically proven health benefits: How to recognize and recommend an effective fiber therapy. J Am Assoc Nurse Pract. 2017 Apr;29(4):216–23. DOI: 10.1002/2327-6924.12447. PMID: 28252255. PMCID: PMC5413815.
  9. Vanhauwaert E, Matthys C, Verdonck L, De Preter V. Low-residue and low-fiber diets in gastrointestinal disease management. Adv Nutr. 2015 Nov 13;6(6):820–7. DOI: 10.3945/an.115.009688. PMID: 26567203. PMCID: PMC4642427.
  10. Burén J, Ericsson M, Damasceno NRT, Sjödin A. A Ketogenic Low-Carbohydrate High-Fat Diet Increases LDL Cholesterol in Healthy, Young, Normal-Weight Women: A Randomized Controlled Feeding Trial. Nutrients. 2021 Mar 2;13(3). DOI: 10.3390/nu13030814. PMID: 33801247. PMCID: PMC8001988.
  11. Crosby L, Davis B, Joshi S, Jardine M, Paul J, Neola M, et al. Ketogenic diets and chronic disease: weighing the benefits against the risks. Front Nutr. 2021 Jul 16;8:702802. DOI: 10.3389/fnut.2021.702802. PMID: 34336911. PMCID: PMC8322232.
  12. El-Salhy M, Ystad SO, Mazzawi T, Gundersen D. Dietary fiber in irritable bowel syndrome (Review). Int J Mol Med. 2017 Sep;40(3):607–13. DOI: 10.3892/ijmm.2017.3072. PMID: 28731144. PMCID: PMC5548066.
  13. North American Society for Pediatric Gastroenterology, Hepatology, and Nutrition. CarbDiet PDF final.pdf.
  14. McRorie JW, McKeown NM. Understanding the Physics of Functional Fibers in the Gastrointestinal Tract: An Evidence-Based Approach to Resolving Enduring Misconceptions about Insoluble and Soluble Fiber. J Acad Nutr Diet. 2017;117(2):251–64. DOI: 10.1016/j.jand.2016.09.021. PMID: 27863994.
  15. Akbar A, Shreenath AP. High Fiber Diet. In: StatPearls. Treasure Island (FL): StatPearls Publishing; 2022. PMID: 32644459.
  16. Barber TM, Kabisch S, Pfeiffer AFH, Weickert MO. The health benefits of dietary fibre. Nutrients. 2020 Oct 21;12(10). DOI: 10.3390/nu12103209. PMID: 33096647. PMCID: PMC7589116.

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