Soluble and Insoluble Fiber: What’s the Difference?

Reviewed by Kathleen M. Zelman, MPH, RD, LD on July 23, 2015

Fiber does way more than just keep you regular. The rough stuff can also help lower cholesterol, keep your blood sugar stable, make it easier to lose weight,, and even help keep you alive longer.

To get all those benefits, there are two types of fiber that your body needs: soluble and insoluble. Both come from plants and are forms of carbohydrates. But unlike other carbs, fiber can’t be broken down and absorbed by your digestive system. Instead, as it moves through your body it slows digestion and makes your stools softer and easier to pass.

Most foods contain both insoluble and soluble fiber but are usually richer in one type than the other. The easiest way to tell them apart: Soluble fiber absorbs water, turning into a gel-like mush (think of what happens when you add water to oatmeal) while insoluble fiber doesn’t (think of what happens when you add water to celery).

Soluble Fiber

Foods rich in this type of fiber include oatmeal, nuts, beans, apples, and blueberries.

The health benefits include:

Heart protection: Inside your digestive system, soluble fiber attaches to cholesterol particles and takes them out of the body, helping to reduce overall cholesterol levels and the risk of heart disease. Oatmeal may offer the most heart protection.

Diabetes protection: Because soluble fiber isn’t well absorbed, it doesn't contribute to the blood sugar spikes that can put you at risk for type 2 diabetes and heart disease. If you already have diabetes (either type 1 or type 2) soluble fiber can even help keep your condition under control.

Weight loss: Soluble fiber can also help you get to -- or stay at -- a healthy weight by keeping you feeling full without adding many calories to your diet.

Healthy bowel movements: Soluble fiber soaks up water as it passes through your system, which helps bulk up your stool and guard against constipation and diarrhea. In fact, most fiber supplements contain mostly soluble fiber.

Insoluble Fiber

This is found in the seeds and skins of fruit (so always eat your peels) as well as whole-wheat bread and brown rice.

The health benefits include:

Weight loss: Like soluble fiber, insoluble fiber can play a key role in controlling weight by staving off hunger pangs.

Digestive health: Eating lots of insoluble fiber also helps keeps you regular, and if you do get constipated, adding more of it to your diet can get things moving. Insoluble fiber can also improve bowel-related health problems, like constipation, hemorrhoids, and fecal incontinence (problems controlling your bowel movements.)

Show Sources


Oregon State University Linus Pauling Institute: Micronutrient Information Center: "Fiber."

University of Colorado, Colorado Springs: "Soluble Fiber vs. Insoluble Fiber."

Cleveland Clinic: "Improving Your Health with Fiber." "Healthy Diet in Adults."

Harvard School of Public Health, The Nutrition Source: "Fiber."

Academy of Nutrition and Dietetics Oncology Nutrition: "Constipation, Diarrhea and Fiber."

Kaiser Permanente: "Fiber Facts: Why Fiber Is Important."

Montefiore Medical Center: "Don't Forget the Fiber in Your Low-Carb Diet."

Tracie Jackson, RD, LMNT, CDE, nutrition therapist, Nebraska Medicine. "Patient information: High-fiber diet (Beyond the Basics)."

Rebecca Blake, RD, director of clinical nutrition, Mount Sinai Beth Israel.

Oregon State University Extension Service: "Fiber - The Fabric of Heart Health."

University of Massachusetts Medical School: "What you can do to LOWER your TRIGLYCERIDES."

Towson University: "Fiber Facts."

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