Fiber Deep Dive

Fiber has long been recognized as a food component that helps keep you regular. But its health benefits go far beyond your bowel movements.

The more we learn about fiber, the more we realize its importance to long-term health. For everything from cancer prevention to immune function, fiber plays a supportive role in regulating body systems and optimizing health.

Let’s look closer at fiber and its role in making your diet the best it can be. We’ll cover:

• What fiber is and the different types
• How fiber works in your gut to support microbiome and intestinal health
• The health benefits of fiber
• How to get the fiber you need

What is Fiber?

Fiber is the name given to components of plant foods that are indigestible by the human body. While their biochemical structure is technically that of a carbohydrate, the small intestine, which is responsible for breaking food down into digestible parts, lacks the enzymes to break down fiber.

Fiber passes through the digestive tract without being absorbed, meaning it doesn’t provide any calories. If this sounds useless, think again. All that fiber adds bulk to your stool, preventing constipation and keeping you regular. But it does so much more, providing unseen benefits that prevent disease.

Fiber comes in many forms, each providing unique benefits.

Soluble Fiber

Soluble fiber attracts and absorbs water, forming a gel-like substance as it passes through the digestive tract. Its main benefits are:

• Slows digestion, helping you feel full sooner and for longer
• Stabilizes blood sugar after a meal
• Captures cholesterol from the digestive tract and causes it to be excreted through stool, helping to lower overall cholesterol levels
• Provides food for the diverse microbes in the gut (more on that later!)

Food sources of soluble fiber include apples, bananas, citrus fruits, beans and legumes, oats, nuts, and psyllium.

Insoluble Fiber

Insoluble fiber does not dissolve in water. Its main benefits are:

• Provides bulk to stools, making them soft and easy to pass
• Keeps food moving through the digestive tract, preventing constipation

Food sources of insoluble fiber include whole grains, nuts, seeds, broccoli, spinach, berries, and wheat bran.

Resistant Starch

While not technically fiber, resistant starches act like fiber by evading digestion in the small intestine and arriving in the colon intact and providing many of the same health effects as soluble fiber. Its main benefits are:

• Providing food for the microbiome
• Regulating blood sugar
• Promotes regular bowel movements
• Supports feelings of satiety after a meal

Food sources of resistant starch include green bananas, oats, barley, white beans, lentils, and cooked and cooled rice and potatoes.

The Many Health Benefits of Fiber

The most well-known of fiber’s actions is the way it supports healthy stools. Pooping may not seem like that interesting of a bodily function, but its effects on overall health are many.

Regular, soft, well-formed bowel movements are important for:

• The removal of waste and toxins
• Managing nutrient and fluid balance
• For women, the secretion of excess estrogen

Fiber keeps these functions humming along smoothly.

Beyond bowel movements, fiber plays an important role in the microbiome

Fiber and the microbiome

The microbiome is the community of microbes, including yeast, fungi, and bacteria, that naturally live in your gut. Your body works in synergy with your microbiome, and the healthier your microbiome, the healthier your entire body will be.

The microbiome influences many critical body functions: [1]

• The digestion and absorption of nutrients
• Immune system regulation
• Protection from pathogens
• Protection against inflammation
• Supporting healthy metabolism and weight control
• Brain health through the gut-brain axis
• And more!

We’re still learning about all the microbiome does.

A healthy microbiome is made up of a diverse balance of microbes. These microbes rely on fiber as their primary food source. So, while your digestive enzymes may not be able to break down fiber, the bacteria in your microbiome take that fiber and ferment it to provide themselves with nourishment. [2]

Fiber and Short-Chain Fatty Acids

When the bacteria in the microbiome ferment fiber, they produce a variety of compounds, the most common and beneficial of which are short-chain fatty acids (SCFAs).

SCFAs are produced in the colon by specific bacteria that ferment fiber and resistant starch. The most common SCFAs are acetate, propionate, and butyrate. Together, these SCFAs perform many beneficial functions and are one of the primary reasons fiber is so important. [3]

• Increase the diversity and quantity of beneficial microbes in the gut
• Improve the function of the intestinal barrier
• Reduces inflammation
• Lowers appetite by stimulating the release of GLP-1s
• Improves insulin sensitivity
• May reduce cancer cell proliferation
• And so much more!

Health Benefits of a High Fiber Diet

A wealth of research has examined the effects of high fiber diets on everything from weight control to cancer prevention. There are decades of data supporting the significant benefits of fiber.

Individuals who consume high-fiber diets have more diverse microbiomes with a better mix of beneficial bacteria. [4] The diversity and robustness of your microbiome can significantly influence your health.

High-fiber diets and a diverse microbiome support:

• Healthy weight maintenance [5]
• Improved insulin sensitivity and a reduced risk of type 2 diabetes [6]
• Reduced risk of cardiovascular disease [7]
• Healthy blood pressure [8]
• Lower cholesterol [9]
• Reduced risk of certain types of cancer [10]

How Much Fiber Do You Need

The standard American diet is sadly lacking in fiber. In fact, as few as 5% of people meet the minimum recommended amount of fiber each day. [11]

Current guidelines recommend a minimum of 14 grams of fiber for every 1000 calories you eat in a day. [12] For most people, that comes out to between 25 to 35 grams of fiber per day.

A good rule of thumb is to aim for a minimum of 30 grams of fiber each day, or 10+ grams at each meal.

Any food that comes from plants contains fiber, though some have more than others. Fruits, vegetables, whole grains, beans and legumes, nuts, and seeds are all good sources of fiber and should feature heavily at every meal.

Tips to Eat More Fiber

• Have a smoothie that includes greens, berries, almonds, and chia seeds
• Add berries and chia seeds to a bowl of oatmeal
• Switch to whole grains, for example, brown rice instead of white, whole-grain bread instead of white bread, high-fiber tortillas instead of regular ones, etc.
• Keep fresh fruits and vegetables around for snacking. Try baby carrots, sliced apples, a pear, sliced peppers, etc.
• Add beans or lentils to soups, salads, and pasta dishes.
• If you struggle with constipation or irregular bowel movements, consider adding psyllium fiber to smoothies or oatmeal.

Final Word

Consuming more fiber is an easy way to significantly improve the healthfulness of your diet. Fiber combats many of the current urgent health crises, including obesity, heart disease, type 2 diabetes, and cancer.

Adding more high-fiber foods to your diet doesn’t require you to upend your current eating pattern, just to sneak in more of the foods you know are good for you anyway. The result will be a diet packed with more nutrients and health-promoting power.

References

1. Sorboni, Shokufeh Ghasemian et al. “A Comprehensive Review on the Role of the Gut Microbiome in Human Neurological Disorders.” Clinical microbiology reviews vol. 35,1 (2022): e0033820. doi:10.1128/CMR.00338-20

2. Fu, Jiongxing et al. “Dietary Fiber Intake and Gut Microbiota in Human Health.” Microorganisms vol. 10,12 2507. 18 Dec. 2022, doi:10.3390/microorganisms10122507

3. Xiong, Ruo-Gu et al. “Health Benefits and Side Effects of Short-Chain Fatty Acids.” Foods (Basel, Switzerland) vol. 11,18 2863. 15 Sep. 2022, doi:10.3390/foods11182863

4. Cronin, Peter et al. “Dietary Fibre Modulates the Gut Microbiota.” Nutrients vol. 13,5 1655. 13 May. 2021, doi:10.3390/nu13051655

5. Menni, C et al. “Gut microbiome diversity and high-fibre intake are related to lower long-term weight gain.” International journal of obesity (2005) vol. 41,7 (2017): 1099-1105. doi:10.1038/ijo.2017.66

6. Salamone, Dominic et al. “The relationship between gut microbiota, short-chain fatty acids and type 2 diabetes mellitus: the possible role of dietary fibre.” Acta diabetologica vol. 58,9 (2021): 1131-1138. doi:10.1007/s00592-021-01727-5

7. Papadopoulos, Panagiotis D et al. “The Emerging Role of the Gut Microbiome in Cardiovascular Disease: Current Knowledge and Perspectives.” Biomedicines vol. 10,5 948. 20 Apr. 2022, doi:10.3390/biomedicines10050948

8. Xu, Chudan, and Francine Z Marques. “How Dietary Fibre, Acting via the Gut Microbiome, Lowers Blood Pressure.” Current hypertension reports vol. 24,11 (2022): 509-521. doi:10.1007/s11906-022-01216-2

9. Soliman, Ghada A. “Dietary Fiber, Atherosclerosis, and Cardiovascular Disease.” Nutrients vol. 11,5 1155. 23 May. 2019, doi:10.3390/nu11051155

10. Hu, Jun et al. “Use of Dietary Fibers in Reducing the Risk of Several Cancer Types: An Umbrella Review.” Nutrients vol. 15,11 2545. 30 May. 2023, doi:10.3390/nu15112545

11. Quagliani, Diane, and Patricia Felt-Gunderson. “Closing America's Fiber Intake Gap: Communication Strategies From a Food and Fiber Summit.” American journal of lifestyle medicine vol. 11,1 80-85. 7 Jul. 2016, doi:10.1177/1559827615588079

12. U.S. Department of Agriculture and U.S. Department of Health and Human Services. Dietary Guidelines for Americans, 2020-2025. 9th Edition. December 2020. Available at DietaryGuidelines.gov.