What's the Difference between Soluble and Insoluble Fiber?

By Tiffany W. | Updated: Jun 22, 2020

What's the Difference between Soluble and Insoluble Fiber?

Dietary fiber occurs naturally in plant foods, and it is essential to a healthy and fully functioning digestive system. Without fiber, the digestive system stops working properly - causing constipation and putting itself at risk of infections as well as chronic diseases.

Fiber helps prevent colon cancer and hemorrhoids, regulates cholesterol levels, and lowers blood sugar. A strong immune system is based on smooth digestion and a healthy stomach flora. In order to keep the both working smoothly, both soluble and insoluble fiber are included in the Centers for Disease Control and Prevention's (CDC) dietary guidelines.

All plant-based foods offer two types of dietary fiber: soluble and insoluble fiber, but, what is the difference between them?

What does Soluble Fiber do?

Soluble fiber absorbs water and turns into a sort of gel that protects the gastrointestinal muscles around the colon - normalizing contractions. Soluble fiber also slows down digestion, soothing and regulating the digestive tract. This type of fiber relieves constipation by softening fecal matter.

Soluble fiber is highly beneficial for people with Irritable Bowel Syndrome (IBS).

Foods high in soluble fiber are seeds, such as chia, flax, and psyllium, as well as fruits, chiefly raspberryapple, and blueberry.

What Does Insoluble Fiber Do?

This is the type of dietary fiber most people are familiar with. The most important benefits of insoluble fiber are:

  • Promoting healthy digestion and relieving constipation. Insoluble fiber helps regulate bowel movements by bulking up stool, which helps it to pass through the digestive track at a faster pace. Insoluble fiber consumption is absolutely necessary for digestive health, but it must be consumed in moderation.

  • Reducing cholesterol. Insoluble fiber has the ability of binding with fats in the intestinal tract and helping eliminate the excess with the stools, thus contributing to significantly lower cholesterol levels.

  • Lowering blood sugar. Once it reaches the stomach, insoluble fiber slows down digestion, allowing the body to properly absorb the nutrients in food and preventing sugar spikes after heavy meals.

The best sources of insoluble fiber are whole grains, like barley, wheat , and sorghum; nuts, like almond, Brazil nut, and pecans; legumes, mainly peanuts, peas, lentils, and beans, as well as vegetables, particularly avocado , and leafy greens, such as spinach.

How to Consume Healthy Amounts of Fiber

Did you know?

The daily fiber intake among adults in the United States averages 15 grams a day, which is about half the recommended daily allowance (RDA) of 25 grams.

A healthy diet requires a balanced amount of both types of fiber, soluble and insoluble, in order to create optimal digestive function. If dietary restrictions prove fiber intake difficult, there are supplements available to aid with digestion. However, eating well-balanced meals is all that you need in order to keep digestion running smoothly.

Some healthy breakfast suggestions for a balanced morning intake of dietary fiber can include a quinoa breakfast bowl, a cup of overnight oatmeal with berries, or a nutritious flax and psyllium bread with chia blueberry jam.

You will know when your body is lacking fiber. The good news is that you can easily make some dietary adjustments to fix the problem.


  • Colorado State University, Extension, Dietary Fiber
  • Harvard University, School of Public Health, The Nutrition Source, Fiber
  • Oregon State University, Linus Pauling Institute, Fiber
  • University of California, San Francisco, UCSF Medical Center, Increasing Fiber Intake
  • MedlinePlus Herbs and Supplements, Soluble vs. insoluble fiber