Published 13th June 2022

Fiber: All you need to know

Diets rich in fiber are associated with good heart health, metabolic health, and gut health. In this article, we’ll dive into what fiber is and how it benefits your health. We’ll also explain how much fiber you should eat and outline some good dietary sources of fiber.

Fiber feeds your gut microbiome — the trillions of microorganisms that live in your gut. Boosting your gut bacteria with fiber helps explain some of the health benefits of a fiber-rich diet.

ZOE scientists are at the forefront of gut microbiome research, running the world's largest nutrition study to date. As a result, we're continuously learning more about how your gut bacteria influence your overall health. 

If you'd like to learn more about the bacteria in your gut, start by taking our free quiz today.

What is fiber?

Fiber is a type of carbohydrate that your body can’t digest. So, instead of being broken down into sugar like other carbohydrates, it passes through your body.

Experts recommend that adult women consume about 25 grams (g) of fiber per day, and adult men should aim for about 35 g per day. 

There are two main categories of fiber: soluble and insoluble. Both are important to include in your diet.

Soluble fiber

Soluble fiber dissolves in water, turning into a gel-like substance in your gut. This helps slow digestion, which can help you feel fuller for longer and reduces the risk of spikes in blood sugar. 

This type of fiber may also help control the amount of “bad” cholesterol in your blood. Soluble fiber is present in oats, barley, nuts, seeds, beans, and some fruits and vegetables.

Insoluble fiber

Insoluble fiber doesn’t dissolve in water. This fiber helps food move through your body and can prevent constipation. Insoluble fiber is present in whole grains — such as brown rice, wheat bran, and quinoa — leafy greens, nuts, seeds, vegetables, and skin-on fruits.

Some specific types of naturally occurring fiber include:

  • Cellulose: Insoluble fiber found in many whole grains, fruits, and vegetables.

  • Lignins: Insoluble fiber found in wheat, corn, nuts, flaxseeds, and vegetables.

  • Pectins: Soluble fiber found in fruit, such as apples and berries.

  • Inulins: Soluble fiber found in onions, asparagus, and chicory root.

Experts also categorize fiber as fermentable or nonfermentable. Fermentable fiber includes those that feed the bacteria in your gut.

Conversely, nonfermentable fiber passes through your intestines and can help promote regular bowel movements.

The health benefits of fiber

Eating enough fiber is an essential part of any healthy diet. For instance, one study involving over 4,600 participants found that a diet rich in fiber was associated with up to 31% lower risk of developing many chronic diseases.

Here are some of the specific health benefits of fiber:

Regular bowel movements

Both soluble and insoluble fiber can help promote regular bowel movements and protect against constipation

As soluble fiber dissolves in water, it produces a gel-like substance, which helps bulk up and soften stool, making it easier to pass. In addition, insoluble fiber interacts with the lining of your intestine, causing water and mucus to enter the colon and promote movement.

Fiber can also help keep you regular by feeding your gut bacteria. As the bacteria in your gut eat and ferment the fiber, water is drawn into your intestines, making your stool softer and easier to pass.

A healthy gut

As we’ve learned, certain types of fiber act as food for the trillions of microorganisms living in your gut, collectively called your gut microbiome

A healthy, diverse gut microbiome can affect many aspects of your health, including the health of your immune system and your metabolic health. It may also protect against other conditions, such as arthritis and eczema. 

Among other factors, how much fiber you eat affects the health of your gut microbiome. For example, in an animal study in the journal Nature, scientists reported that when mice ate a low-fiber diet for 4 weeks, they experienced a 60% decrease in microbe diversity. 

A 2-week clinical trial with human participants showed that switching to a high-fiber diet significantly increased the participants' good bacteria.

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Lower cholesterol

Cholesterol is vital for many bodily functions, but too much cholesterol in the blood increases the risk of cardiovascular diseases, including stroke and heart attack.

A fiber-rich diet lowers cholesterol in a few different ways. For instance, soluble fiber traps cholesterol in the gut. This prevents it from being absorbed back into the blood. Instead, it leaves your body in poop.

Also, fiber feeds the “good” bugs in your gut. As the bacteria break down fiber, they produce short-chain fatty acids (SCFAs). These fatty acids reduce cholesterol production in the liver, lowering blood cholesterol levels.

When SCFAs enter the blood, they also help regulate your metabolism.

Heart health

According to the American Heart Association, heart disease is the leading cause of death worldwide. However, a wealth of evidence suggests that eating a fiber-rich diet is associated with a lowered risk of heart disease and death

In addition to lowering cholesterol levels, a high-fiber diet is associated with reducing other risk factors for heart disease, such as high blood pressure and obesity.

Blood sugar control

After you eat, most of the carbohydrates in your food are broken down into sugar. This sugar enters your blood and gets transported to your cells to use for energy. 

Increases in blood sugar are normal, but a lot of sugar entering your blood at once can cause blood sugar spikes, and over time, this can negatively affect your health.

Fiber can help your blood sugar levels rise more gradually. During digestion, soluble fiber dissolves in water, creating a gel that slows digestion and allows the sugars in your food to enter your bloodstream at a slower pace. 

ZOE scientists have shown that everyone’s blood sugar levels respond differently to foods.

Even identical twins can have different responses to the same food. As part of our at-home test, we measure your blood sugar levels after you eat, helping you understand how you respond to food.  

Protection against some cancers

Higher fiber intake is associated with a lower risk of colorectal, breast, and esophageal cancers and cancer mortality.

In one study involving more than 90,000 premenopausal women, researchers found that the women who ate fiber-rich diets during childhood and early adulthood had a 25% lower risk of developing breast cancer than those who ate the lowest amount of fiber.

Possible weight loss

As mentioned above, fiber can help you feel fuller longer. If you’re looking to lose weight, fiber might be able to help.

At ZOE, we know how challenging weight loss can be. We also know that there is no one-size-fits-all approach to weight loss because everyone responds differently to food. This is why personalized nutrition is important.

Unpublished data from ZOE shows that people who closely followed our personalized nutrition program lost an average of 9.4 pounds after 3 months. Around 80% said they didn’t feel hungry and had more energy. 

To find out more about the ZOE program, take our free quiz today.

What foods are high in fiber?

Vegetables, skin-on fruit, whole grains, beans, seeds, and nuts are generally good sources of fiber. To help build a diverse, healthy gut microbiome, eat a range of different fibers from various sources.

If you’re looking to add more fiber to your diet, consider adding foods such as:

  • pinto beans: 15 g of fiber per cup

  • baked beans: 14 g of fiber per cup

  • lima beans: 13 g of fiber per cup

  • bran cereal: 10 g of fiber per half cup 

  • raspberries: 8 g of fiber per cup

  • whole-wheat pasta: 6 g of fiber per cup

  • dried prunes: 6 g of fiber per 10 prunes

  • artichoke: 6 g of fiber per one medium artichoke

  • baked potato with skin: 5 g of fiber per medium potato

  • canned pumpkin: 5 g of fiber per half cup

  • kiwi: 5 g of fiber per cup

  • brown rice: 4 g of fiber per cup 

  • peas: 4 g of fiber per half cup

  • pears: 4 g of fiber per 1 medium pear 

  • blueberries: 4 g of fiber per cup

While it’s best to get fiber from natural, whole-food sources, fiber supplements and fiber-fortified foods are also available. Additionally, doctors may prescribe supplements to some people. 

Tips for a high-fiber diet

If you want to add more fiber to your diet, here are some tips to get you started.

  • Start small with plenty of water. Adding too much fiber too quickly or without enough water can lead to uncomfortable side effects like cramping, excessive gas, or constipation.

  • Be active. Movement is important when you increase your fiber intake, to avoid constipation.

  • Eat the skin. Most of the fiber in fruits and vegetables is present in the skin. Eat potatoes, apples, and pears, for example, with the skin on. Just make sure to rinse them first.

  • Switch to whole grains. Whole grains have far more fiber than their refined-grain counterparts. Whole grain pasta, breads, oats, barley, brown rice, quinoa, and other whole grains are widely available in most grocery stores.

  • Try plant-based proteins. Beans, lentils, split peas, and other plant protein sources are typically high in fiber and can be added to or take the place of meat. For example, try swapping half of your ground meat with black beans next taco night.

  • Add fruits and vegetables. An easy way to boost the fiber in your favorite dishes is to add fruits or vegetables. For example, toss spinach into chicken noodle soup. Add berries and oats to your morning yogurt. The possibilities are endless.

  • Enjoy nuts and seeds. You can sprinkle these on salads and soups, and include them in smoothies. 

ZOE’s research has shown that there is no one-size-fits-all approach to nutrition. That’s why we focus on understanding which foods suit your body best.

When you join ZOE, you’ll take an at-home test to measure how your blood sugar and blood fat levels respond to food. We’ll also analyze your gut microbiome. 

Using this information, we can give you tailored nutrition advice to ensure that you’re eating the best foods for your body and your gut microbiome. 

Take our free quiz today to find out more. 

Summary

Fiber is a type of carbohydrate that your body doesn’t digest. There are two main types of fiber, soluble and insoluble, and both are good for your health.

Eating enough fiber benefits your health, including promoting heart and gut health. Fiber may also help you control your blood sugar, reduce cancer risk, and possibly lose weight.

Sources

Association between dietary fiber and lower risk of all-cause mortality: A meta-analysis of cohort studies. American Journal of Epidemiology. (2015). https://academic.oup.com/aje/article/181/2/83/2739206

Carbohydrate quality and human health: a series of systematic reviews and meta-analyses. The Lancet. (2019). https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(18)31809-9/fulltext#seccestitle10

Chronic constipation: is a nutritional approach reasonable? Nutrients. (2021). https://www.mdpi.com/2072-6643/13/10/3386/htm

Diet and lifestyle factors and risk of atherosclerotic cardiovascular disease — a prospective cohort study. Nutrients. (2021). https://www.mdpi.com/2072-6643/13/11/3822

Dietary fiber and blood pressure control. Food & Function. (2016). https://pubmed.ncbi.nlm.nih.gov/26923351/

Dietary fiber, gut microbiota, and metabolic regulation - current status in human randomized trials. Nutrients. (2020). https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7146107/

Dietary fiber intake in young adults and breast cancer risk. Pediatrics. (2016). https://www.publications.aap.org/pediatrics/article-abstract/137/3/e20151226/81373/Dietary-Fiber-Intake-in-Young-Adults-and-Breast?redirectedFrom=fulltext

Dietary fibers reduce obesity-related disorders: mechanisms of action. Clinical Nutrition and Metabolic Care. (2020). https://journals.lww.com/co-clinicalnutrition/Abstract/2020/11000/Dietary_fibers_reduce_obesity_related_disorders_.12.aspx

Dietary Guidelines for Americans. (2020). https://www.dietaryguidelines.gov/sites/default/files/2020-12/Dietary_Guidelines_for_Americans_2020-2025.pdf

Diet-induced extinction in the gut microbiota compounds over generations. Nature. (2016). https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4850918/

Fiber. (n.d.). https://www.hsph.harvard.edu/nutritionsource/carbohydrates/fiber/

Fiber in foods chart. (n.d.) https://www.med.umich.edu/mott/pdf/mott-fiber-chart.pdf

Food ingredients that inhibit cholesterol absorption. Preventive Nutrition and Food Science. (2017). https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5503415/

Heart disease and stroke statistics — 2021 update. Circulation. (2021). https://www.ahajournals.org/doi/10.1161/CIR.0000000000000950

High-fiber, whole-food dietary intervention alters the human gut microbiome but not fecal short-chain fatty acids. mSystems. (2021). https://journals.asm.org/doi/10.1128/mSystems.00115-21

Management of chronic constipation in adults. United European Gastroenterology Journal. (2016). https://journals.sagepub.com/doi/10.1177/2050640616663439

Role of the gut microbiota in nutrition and health. BMJ. (2018). https://www.bmj.com/content/361/bmj.k2179

Short-chain fatty acids in control of energy metabolism. Critical Reviews in Food Science and Nutrition. (2016). https://web.archive.org/web/20190224214544id_/http://pdfs.semanticscholar.org/5e5d/eb4d34ccac839dea0bf938a8bfdd00f6a350.pdf

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