Although gut health is not the hottest nutrition topic right now (protein, we’re looking at you!), the importance of healthy digestive function is undeniable. From managing constipation and diarrhea to food sensitivities and preventing disease, your gastrointestinal (GI) system can help you feel strong and vibrant or in the toilet, literally.
At the center of good gut health? Fiber—a nutritional powerhouse we simply can’t overlook.
Unfortunately, most people don’t get enough fiber, and some avoid it altogether due to discomfort. But with a little knowledge and the right approach, you can reap all the benefits fiber has to offer.
Let’s explore what fiber is, its benefits, and how to incorporate it into your diet for better health and vitality.
What is fiber?
Fiber is a type of carbohydrate found in plant-based foods that humans can’t fully digest because we lack the appropriate digestive enzymes. While we can’t digest or absorb fiber, it offers countless health benefits as it travels through our digestive system.
At the highest level, fiber is divided into two types:
- Dietary fiber: Naturally present in plant foods like fruits, vegetables, grains, and legumes. This is what you see listed on Nutrition Facts Labels.
- Functional fiber: Isolated or synthetic forms of fiber, added to foods or sold as supplements, proven to provide health benefits.
Dietary and functional fiber have unique properties that affect how they function in your body:
- Solubility: Soluble fiber dissolves in water, while insoluble fiber does not.
- Fermentability: Fermentable fibers (prebiotics) feed the beneficial bacteria in your gut. Non-fermentable fiber is indigestible by us and our gut bugs.
- Viscosity: Viscous fibers soak up water and digestive juices in the digestive tract, forming a thick gel. Viscosity is determined by the:
- Solubility of the fiber,
- pH (i.e., acid level) of the GI tract,
- Size of the fiber particles, and
- Amount of processing done to the fiber before consumption.
- Adsorption: Fiber binds to substances such as nutrients, enzymes, hormones, and toxins in the intestine, aiding in detoxification.
Each of these characteristics determines how fiber supports your health.
Here is a summary of the types of fiber and their properties:
| Fiber Types | Dietary or Functional? | Soluble? | Fermentable? | Viscous? | Adsorption? |
|---|---|---|---|---|---|
| Cellulose | Both | No | Poorly | No | Unknown1 |
| Hemicellulose | Dietary | Both | Both | No | Some |
| Pectin | Both | Yes | Yes | Highly | Yes |
| Lignin | Both | No | Poorly | No | Yes |
| Gums | Both | Yes | Yes | Yes | Yes |
| Beta-glucans2 | Both | Yes | Yes | Highly | Yes |
| Fructans3 | Both | Yes | Yes | No | Some (inulin for sure) |
| Glucomannan | Both | Yes | Yes | Highly | Yes |
| Resistant Starch Type 1: Located within the cellulose wall Type 2: Located in granules within plant cells Type 3: “Retrograde starch” Type 4: Chemically modified starch | 1, 2, 3 = Dietary 4 = Functional | No | 1, 2 = Yes 3, 4 = Partially | No | Unknown1 |
| Chitin and Chitosan | Functional | Some chitosans only | Poorly | Yes | Some chitosans only |
| Polydextrose and polyols | Functional | Yes | Partially | Yes | Some |
| Psyllium | Functional | Yes | Yes | Yes | Yes |
| Resistant dextrins | Functional | Yes | Yes | No | Unknown1 |
1: Inadequate information is available.
2: Beta-glucans are a type of hemicellulose, but are separated here as they have been found to adsorb cholesterol, therefore, lowering the risk of heart disease.
What does fiber do for your body?
Even though we consume it, the purpose of fiber is not to provide energy to our bodies. Rather, fiber is a multi-tasking superhero for your digestive system and beyond.
Depending on its type, fiber can:
Soluble vs. Insoluble fiber
- Soluble fiber slows digestion, helping to:
- Prolong feelings of fullness (a win for weight management),
- Reduce diarrhea by slowing gut transit time, and
- Stabilize blood sugar levels by reducing glucose absorption.
- Insoluble fiber speeds up digestion, helping to:
- Prevent constipation by increasing stool bulk, and
- Keep waste moving efficiently through your intestines.
Fermentable vs. Non-fermentable fiber
- Fermentable fiber feeds and encourages the reproduction of beneficial gut bacteria, who then:
- Help keep unhelpful gut bugs in check;
- Produce short chain fatty acids (SCFAs), which:
- Increase absorption of sodium and water in the colon,
- Provide energy to the cells of the colon,
- Improve blood flow to the colon, which improves constipation,
- Encourage growth of new cells in the colon,
- Inhibit formation of tumors (i.e., reduces the risk of colon cancer), and
- Boost immune system function; and
- Release vitamins, including K, B12, biotin, folate and thiamine, which can be absorbed into the blood stream
- Non-fermentable fiber adds bulk to stool, aiding in regularity without feeding gut bacteria—a bonus for those with bloating or IBS.
Important Note: Feeding beneficial gut bacteria is important for our health. After all, you can take all the probiotics you want, but if you don’t feed them, they won’t stick around to provide health benefits. On the other hand, people who struggle with bloating, excessive flatulence, and IBS may feel worse when consuming fermentable fiber.
Viscous fiber
Viscous fibers absorb water to form a thick gel, which:
- Increases the volume of the stool for easier elimination,
- Speeds up the transit time, aiding in regularity,
- Reduces the nutrients available for absorption by interfering the with interaction between digestive enzymes and food, and
- Slows nutrient absorption, which helps prevent a blood sugar spike.
Adsorption
Adsorbing fiber binds to various substances in your digestive tract so they cannot be absorbed, such as:
- Bile salts, which lowers blood cholesterol,
- Toxins, nitrogenous waste, and carcinogens, which lowers the risk of some cancers and other diseases,
- Excess hormones like estrogen, and
- Nutrients such as fat, calcium, magnesium, zinc, iron, carotenoids and some phytonutrients.
What are fiber’s health benefits?
Fiber’s benefits can be felt throughout the body, even though it is never absorbed into the blood stream. Incorporating enough fiber into your diet supports:
- Digestive Health: Preventing constipation, diarrhea, and gut discomfort,
- Heart Health: Lowering LDL and total cholesterol and reducing heart disease risk,
- Blood Sugar Control: Preventing blood sugar and insulin spikes and protecting against type 2 diabetes,
- Weight Management: Helping you feel fuller for longer,
- Hormone Balance: Reducing the risk of hormone-related cancers, such as prostate, endometrial, breast, and ovarian cancer,
- Detoxification: Binding with toxins to eliminate them from the body,
- Immune System Support: Reducing inflammation, strengthening the immune system, and reducing the risk of allergies, and
- Longevity: Studies link high fiber intake to longer, healthier lives—even in people with chronic illnesses.
How much fiber do you need?
According to the National Academies of Science, the following are the minimum amounts (or Adequate Intake [AI]) for daily fiber intake.
| Age | Females* | Males* |
|---|---|---|
| < 1 year | N/A | N/A |
| 1 – 3 years | 14 g | 14 g |
| 4 – 8 years | 17 g | 20 g |
| 9 – 13 years | 22 g | 25 g |
| 14 – 18 years | 25 g | 31 g |
| 19 – 30 years | 28 g | 34 g |
| 31 – 50 years | 25 g | 31 g |
| 51+ years | 22 g | 28 g |
| Pregnant 1st trimester 2nd trimester 3rd trimester | 25 – 28 g 31 – 34 g 34 – 36 g | N/A |
| Lactating | 31 – 34 g | N/A |
* “Female” is for those assigned female at birth or with an estrogen-dominant profile and “Male” is for those assigned male at birth or with a testosterone-dominant profile.
The FDA sets the daily value for fiber at 28 g based on a 2,000 calorie diet.
Aim for at least these amounts, adjusting based on your health and goals.
What are the best food sources of fiber?
All plant foods contain fiber, as fiber is a form of carbohydrate that creates structure and form. Here are some of the best sources for each type of fiber:
- Cellulose: bran (including from wheat, barley, rice, corn and oats), legumes, nuts, seeds, peas, root vegetables, cruciferous vegetables (including cabbage, brussels sprouts, cauliflower and broccoli), and apples
- Hemicellulose: bran, nuts, legumes, skin of some fruits and vegetables, including beets, potatoes and tomatoes
- Pectin: most fruits, but especially apples, apricots, cherries, quince, plums, gooseberries, oranges and other citrus fruits; some vegetables (like carrots, beets and cabbage) and legumes
- Lignin: the stems and seeds of most fruits and vegetables, especially wheat, mature root vegetables, flaxseed, fruits with edible seeds (like raspberries), and bran
- Gums: found naturally in oats, barley and legumes, but often extracted from plants and used as a thickener in various foods (you’ll recognize it on the label as gum arabic, gellan gum and guar gum). Note: studies have shown eating a large amount of gums, which is really only possible when consuming it as a food additive, causes digestive upset for some people.
- Beta-glucans: oats and barley (primarily), rye, wheat, baker’s yeast and some mushrooms
- Fructans: wheat, rye, barley, onions, leeks, garlic, Jerusalem artichokes, asparagus, corn, beets, brussels sprouts, broccoli, savoy cabbage, radicchio, fennel, chicory, peas, cashews, pistachios, nectarines, peaches and watermelon
- Glucomannan: elephant yam (aka, konjac), which is used to make shirataki noodles and konjac gel, is the only food source that I could find and seems to be the beginning material of glucomannan supplements
- Resistant Starch (types 1, 2 and 3): whole grains, legumes, seeds, unripe bananas, plantains, raw potatoes, cooked and cooled starches (including rice, pasta, corn and potatoes)
If you are consuming lots of vegetables and fruits (especially with the skin on, where appropriate), legumes, nuts, seeds, and whole grains (the more “whole” the better), then you will be getting plenty of fiber. In fact, this is one of the reasons that a plant-centric diet is so beneficial to our health!
That said, it’s important to note that consuming grains—especially in large amounts—may not align with your health goals. While whole grains do contain fiber, many grain-based products are so highly processed that they lose their fiber content. Additionally, whole grains lack the vibrant phytonutrients found in colorful vegetables and fruits, such as those in red, orange, green, purple, blue, or black produce that are essential to our overall health. Finally, if you have sensitivities to gluten or other components of grains, it’s essential to avoid them to prevent adverse reactions, even while striving to increase your fiber intake.
How do I increase my fiber intake?
Boosting your fiber intake can be simple and manageable when done step by step. Start by adding more whole fruits and vegetables to your daily meals. For example, try eating an extra apple or a handful of baby carrots each day. Once that becomes a habit, build on it by adding another serving of fruits or vegetables, and continue to gradually increase from there.
You can also make small dietary swaps to increase your fiber intake. Choose whole grain bread for your sandwich instead of white bread. Swap your morning cereal for chia seed pudding. Add a spoonful of ground flaxseed to your oatmeal for a fiber-rich start to the day.
If you find it challenging to meet the recommended fiber intake from whole foods alone, consider incorporating a fiber supplement into your routine. Supplements can be a helpful addition on days when your diet falls short. (See below for my recommendations.)
That said, don’t rush to make all these changes at once! Increasing fiber gradually is key to avoiding digestive discomfort. Your body needs time to adjust to higher fiber levels, and taking it slow helps ensure a smoother transition. As your system adapts, you can continue to increase your intake until you reach the recommended amount for your age group.
If digestive issues persist despite these changes, it’s a good idea to consult a healthcare provider who can help identify and address any underlying concerns.
What if I have constipation or increasing my fiber intake constipates me?
The most common cause of constipation is dehydration. Your body needs adequate water to keep your stool soft and easy to pass. If you struggle with constipation, increase your fluid intake before adding more fiber to your diet.
If you’re not currently constipated, it’s still essential to drink more water as you increase your fiber intake. Without enough fluid, fiber can become dense and hard, potentially leading to constipation.
If drinking more water and eating more fiber doesn’t resolve constipation, consult a healthcare provider to identify the root cause of your digestive issues and find an appropriate solution.
Are fiber supplements healthy?
While it’s ideal to get all the nutrients your body needs from food, meeting your daily fiber needs through diet alone can be challenging at times. A fiber supplement can be a helpful tool, especially if it improves your digestion. For example, I personally use a fiber supplement most days because I’ve found it supports regularity, even when I’m eating plenty of plant-based foods.
If you choose to use a fiber supplement, look for one that is as natural as possible. Avoid highly processed functional fibers and overly commercialized products.
Ideally, select one that has both soluble and insoluble fiber, as indicated on the Nutrition Facts Label. Although solubility isn’t more important than other characteristics, it often relates to fermentability and viscosity, as all viscous fibers and most fermentable fibers are soluble.
Here are the fiber supplements that I recommend:
- Garden of Life Super Seed: My go-to for ~15 years, though other Garden Life fibers are also excellent.
- Thorne FiberMend
- Ther-Biotic BiotaGen: A capsule option for those who prefer not to use powders.
- NOW Foods Supplements Psyllium Husk Powder
- Ground flaxseeds: Store whole flaxseeds in the fridge to prevent rancidity and grind small amounts as needed.
Important Note: Many fibers can bind to nutrients, vitamins, minerals, and medications, potentially reducing their effectiveness. To avoid this, don’t take supplements or medications within 30 minutes of a fiber supplement. Taking fiber between meals can also ensure better absorption of nutrients from your food.
How do FODMAPs fit into the fiber equation?
FODMAPs—short for Fermentable Oligosaccharides, Disaccharides, Monosaccharides, And Polyols—are fermentable carbohydrates that can cause digestive issues for some people. Research from Monash University in Australia has shown that some individuals who believe they are gluten-sensitive may actually be reacting to FODMAPs found in wheat, rye, and barley.
For people with Irritable Bowel Syndrome (IBS), a low-FODMAP diet may be recommended. However, this diet is highly restrictive and can be difficult to follow. I believe in removing as few foods as possible to find relief, while also addressing the underlying causes of digestive discomfort, which may not be a food sensitivity.
For some individuals, following a low-FODMAP diet might be the only way to achieve complete relief, in which case the restrictions may be worth it. However, I encourage a tailored approach that balances symptom relief with dietary flexibility.
Conclusion
Adding fiber to your diet doesn’t have to be overwhelming and can yield incredible benefits throughout your body. Start by incorporating more plant-based foods into meals and snacks, remembering that a variety of fibers offers the greatest benefits!
If you’re not sure where to start with your personalized fiber plan, book a 1-on-1 consultation and together we’ll create a plan that works for you.
Image by Stephanie Dunne.
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— National Institutes of Health Office of Dietary Supplements. Daily Values. In Dietary Supplement Label Database. Accessed on November 20, 2024.
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— Xu, X., Zhang, J., Zhang, Y., Qi, H., & Wang, P. (2022). Associations between dietary fiber intake and mortality from all causes, cardiovascular disease and cancer: a prospective study. Journal of Translational Medicine, 20(1). https://doi.org/10.1186/s12967-022-03558-6
