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Soluble vs. Insoluble Fiber: What’s the Difference?
Aug 20, 2024
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Different types of fiber have different effects on the body. Learn more about soluble and insoluble fiber and how they contribute to a healthy diet.
Key Takeaways
- Fiber is a type of carbohydrate that can’t be broken down by the digestive system.
- Experts recommend women consume 22–25 grams (g) of fiber daily and men consume 28–34 g daily.
- More than 90% (300 million) of U.S. men and women don’t get enough fiber in their diet.
- Soluble fiber can help regulate bowel movements, blood sugar, and cholesterol levels.
- Other benefits of eating enough fiber include weight management, colon cancer prevention, and reduced inflammation.
Eating well at any age includes balancing your diet with health-promoting foods. Fiber is a part of the diet that most people overlook, yet it has many benefits for digestive health and even chronic disease prevention. Read on to learn more about the difference between fiber types, the benefits of fiber in the diet, and how you can ensure you get enough.
What is fiber?
Fiber is a type of carbohydrate that is part of the structure of plants. Although carbohydrates, such as starches found in wheat flour or potatoes, can be broken down into sugars by the digestive system and used for energy, fiber can’t be digested because humans lack the enzymes needed to do so. Yet fiber is an essential part of a healthy diet that can help with digestion and blood sugar regulation.
Soluble vs. insoluble fiber
There are two types of fiber: soluble and insoluble. Both pass through the digestive tract in different ways and have different effects on digestion.
Soluble fiber can dissolve in water. It absorbs water and forms a gel-like substance to make stool “bulky” but also easier to pass. It slows down the rate of digestion and can help with decreasing cholesterol absorbed into the blood. Soluble fiber can be found in foods like beans, oats, apples, avocados, and okra. Foods with soluble fiber are often used to naturally thicken foods when added to liquid, for example, oats in oatmeal and oranges in marmalade.
The following are types of soluble fiber and where they come from:
- Pectin: Found in fruits and vegetables, apples, bananas, beets, citrus, and okra
- Gums: Found in grains, beans, seaweed, and legumes
- Mucilage: Found in plants that secrete a gluey substance around the roots or seeds, such as psyllium
Insoluble fiber can’t dissolve in water. It passes through your digestive system whole and helps stimulate the movement of contents through the digestive system. Insoluble fiber helps control blood sugar and stimulates regular bowel movements. It can be found in foods such as whole wheat flour, seeds, and the skins of fruits and vegetables.
The following are types of insoluble fiber and where they come from:
- Cellulose: Found in all plant foods, especially the outer layers (peels and stems)
- Hemicellulose: Found in all plant foods and may be used to make vegetarian capsules
- Lignin: Found in woody plants; fruits with edible seeds; brazil nuts; and tougher, more fibrous vegetables
- Bran: Found in the outer layer of whole grains
Both soluble and insoluble fiber are important for proper digestion, regular bowel movements, and a healthy metabolismⓘ The processes in the body that convert and use energy, for example, digesting food or using your muscles. .
What are the benefits of fiber?
Fiber isn’t only good for digestion; it also benefits blood glucose, cholesterol levels, weight management, and more.
Regular bowel movements
Dietary fiber comes from plant foods and adds bulk to food passing through the digestive system. Soluble fiber attracts water to make the stool bulky but also comfortable to pass. Insoluble fiber remains unchanged to add bulk to stool and help with regular bowel movements. Fiber helps regulate bowel movements in people with constipation and irritable bowel syndrome (IBS). Regular bowel movements are important in preventing the long-term effects of constipation, such as abdominal discomfort, hemorrhoids, anal fissures, and inflammation.
Blood sugar regulation
Fiber regulates blood sugar by slowing down the rate at which food is digested and passes through the gut. When mixed with liquids during digestion, soluble fibers form a thick gel, which can trap other carbohydrates from being digested quickly, reducing the amount of glucose (sugar) absorbed into the blood at a time.
Minimizing glucose spikes in the blood after meals helps with the body’s insulin responseⓘ A hormone that the pancreas secretes in response to food intake. It signals for the body’s cells to take in sugar from the blood for energy. In type 2 diabetes, the body doesn’t respond properly to insulin’s signal. as well, which is important in preventing and managing metabolic conditions like diabetes.
Lowering cholesterol
Similar to how fiber can trap carbohydrates and slow their absorption, fiber can also lower the amount of dietary cholesterol absorbed. Dietary fiber can lower total cholesterol and LDL cholesterolⓘ A test measuring the concentration of low-density lipoprotein (LDL) cholesterol in the blood. LDL cholesterol is sometimes called “bad” cholesterol because its high concentrations are associated with increased risk of heart attack and stroke. in the blood. Beta-glucans (β-glucans) are a type of fiber found in plants such as oats and bran that help reduce cholesterol levels in the blood by trapping fats and bile salts (a substance that binds to cholesterol in the gut).
Weight management
In addition to helping with blood sugar control, dietary fiber can help with maintaining healthy weight goals. Soluble fiber slows down stomach emptying and the rate of digestion, meaning it can help you feel full after a meal and regulate your appetite. One review found that people with obesity ate fewer calories, felt fuller, and lost weight just by adding 14 g of fiber to their daily diet.
Read our review of the best weight loss programs to learn more about diets that can support healthy weight management.
Prevention of colon cancer
Colon cancer is a common and serious form of cancer among Americans. People who consume more fiber in their daily diet are less likely to develop colon cancer. Though the exact reasons why are still being studied, fiber may prevent the development of colon cancers through its effects on regulating bowel movements and its anti-inflammatory benefits.
Experts recommend colon cancer screening for all adults ages 45–75. Talk to your primary health care provider to stay up to date with your health screenings.
Overall health and lifespan
Similar to the way fiber helps with colon cancer prevention, studies have found that it also reduces inflammation. One reason is our gut bacteria. Although the human body can’t digest fiber on its own, human gut bacteria can digest some fibers (sometimes called prebiotics) and produce substances that can help reduce inflammation, improve metabolism, and regulate appetite.
Since inflammation is a major factor in the development and management of many chronic diseases, dietary fiber can also help reduce the risk of depression, digestive conditions like IBS, and even heart disease. Because of its many benefits, dietary fiber has also been associated with a decreased risk of death due to any cause.
Risks of too much fiber
It’s possible to have too much fiber. In people who aren’t used to eating a certain amount of fiber, too much fiber can lead to bloating, gassiness, or diarrhea. In addition, when there’s not enough water or fluid intake, people can become constipated or have bowel obstruction. Drinking more water and slowly increasing your daily fiber intake are ways to decrease the side effects of too much fiber.
People with the following conditions may need health care professionals to monitor their fiber intake:
- Crohn’s disease
- Ulcerative colitis
- Intestinal obstruction
- Malabsorption
- Bowel surgery recovery
Because of changes in their intestinal elasticity, older adults are more at risk of constipation and intestinal obstructions. It’s important to drink enough water daily to avoid constipation while eating high-fiber foods.
Every person responds differently to foods, especially when changing dietary habits. That’s why it’s important to consult with a health care provider to ensure your dietary changes will support your overall health.
How much fiber do you need?
Most U.S. adults don’t get enough fiber in their diets. About 96% of men and 92% of women in the United States—more than 300 million Americans— don’t meet their recommended daily intake of fiber. The U.S. Department of Agriculture (USDA) Dietary Guidelines for Americans recommend that adults eat 22–34 g of fiber daily. Your daily recommended intake of fiber depends on your age, gender, and other factors like your health conditions and goals.
Table 1 Recommended daily fiber intake according to the USDA
| Age | Men | Women |
|---|---|---|
| 18–50 | 31–34 g | 22–28 g |
| 51 and older | 28 g | 22 g |
Tips for getting more fiber
Here are some ways to incorporate high-fiber foods into your diet and make sure you meet your recommended daily fiber intake:
1. Add high-fiber breakfast foods.
Here are some high-fiber foods you can add to your breakfast:
- One cup of bran flakes cereal: 10 g of fiber
- Half a cup of oatmeal, made with steel-cut oats: 8 g of fiber
- One medium orange: 3 g of fiber
- Three fresh figs: 4 g of fiber
2. Switch to whole grains.
Whole grains, such as whole wheat and brown rice, have not had the outer bran and germ layers removed. Refined grains (white flour, white rice) have been processed to remove the bran and germ, reducing the fiber content. Two slices of white bread contain 1 g of fiber, while two slices of whole wheat bread have 4 g of fiber. Choosing whole wheat flour and brown rice instead of white rice are easy ways to increase your fiber intake..
Other examples of whole grains are bulgur, couscous, quinoa, buckwheat, and whole oats.
3. Incorporate pulses and beans as ingredients.
Beans are a type of pulse, the seeds of a legume plant. Not all pulses are beans. Examples of pulses are lentils, peas, chickpeas, and soybeans. Beans and other pulses are great ingredients that incorporate a good amount of fiber (and plant-based proteins) into your diet. You can add them to salads, make them into soups (e.g., lentil soup or white bean soup), serve as side dishes (e.g., bean chili or baked beans), or swap them for grains in desserts (e.g., black bean brownies). Here’s how much fiber is in some common pulses and beans:
- One cup of cooked lentils: 8 g of fiber
- Half a cup of cooked pinto beans: 8 g of fiber
- Half a cup of cooked black beans: 8 g of fiber
- One cup of cooked green peas: 9 g of fiber
4. Choose high-fiber fruits and vegetables.
Choosing fruits and vegetables in the form of fresh produce is a way to add more fiber and more whole foods to your diet. Some examples of fruits and vegetables high in fiber:
- One cup of cooked artichokes: 10 g of fiber
- One cup of cooked Brussels sprouts: 6 g of fiber
- One cup of cooked parsnips: 6 g of fiber
- One cup of cooked broccoli: 5 g of fiber
5. Snack on fiber-rich foods.
Snacks like snack cakes and potato chips tend to be highly processed and low in fiber. Nuts, seeds, fruits, and vegetables can make for tasty snacks that help you reach your daily fiber goals. A few examples of fiber-rich snacks:
- One ounce pumpkin seeds: 5 g of fiber
- One ounce of almonds: 4 g of fiber
- One cup of blackberries: 8 g of fiber
- One medium pear: 6 g of fiber
- One cup of raw carrots: 4 g of fiber
Bottom line
Fiber is an important part of a healthy diet. Soluble fiber absorbs water and can help with regularity, blood sugar control, and cholesterol control. Insoluble fiber stays unchanged while going through the digestive system and helps with bowel regularity and blood sugar control. Dietary fiber can also help with weight management, colon cancer prevention, and overall health.
Most Americans don’t meet their daily recommended intake of fiber, which is between 22–34 g. You can get more fiber in your diet by choosing high-fiber foods and whole grains throughout the day instead of processed foods. People with digestive issues or who are starting on a high-fiber diet should work with their health care team to form a nutrition plan that works for them.
Have questions about this article? Email us at reviewsteam@ncoa.org.
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