The Difference Between Soluble and Insoluble Fiber

What’s the difference between soluble and insoluble fiber, and why should we care? Dietary fiber is an important part of your diet.  That much is clear.  But you often hear of the terms soluble and insoluble fiber.  What does that mean? Let’s take a quick look.

Dietary Fiber

Before we get to soluble vs. insoluble fiber, lets learn what fiber is.  Fiber is basically an indigestible component of plants.  Fiber is important for digestion as it impacts how foods are digested and make their way through the intestine.  Fiber also makes you feel full longer, so a diet with an adequate supply of fiber will help to control your appetite.  Both soluble and insoluble fiber are good for you.

For a healthy diet, you should aim for at least 25 grams of fiber every day.  It is not as important what the breakdown of soluble vs. insoluble fiber is in that 25 grams.  Just hitting that number in total is a great start.  Now let’s look at the difference.

Soluble Fiber

Soluble fiber absorbs water in the colon and ferments, changing into a gas.  In fact, soluble fiber dissolves in water.  Some studies have shown that this fermented fiber helps the body to absorb minerals.  When soluble fiber absorbs water it turns into a gel that slows down digestion.  This is what makes you feel full longer.

Good sources of soluble fiber include oatmeal, legumes, some common fruits like the inside of apples and pears, carrots, sweet potatoes, and psyllium.

Insoluble Fiber

Insoluble fiber absorbs water in the colon but does not ferment.  Therefore no byproduct or gas is created.  Insoluble fiber does not change but simply moves through the colon and aids in digestion.  Insoluble fiber helps to prevent constipation.  Insoluble fiber won’t dissolve in water.  Since it doesn’t change in your system it simply moves things along and speeds up the process.

Good sources of insoluble fiber include whole grains, bran and barley, nuts and seeds, green beans, and brown rice.

Fiber Calories


One thing you may not know is that fiber does not technically add calories to your diet.  Because fiber passes through your system instead of being digested by it, energy is not used.  Thus, fiber is a calorie free component of your food.  However, there is debate over the presence of calories in soluble fiber due to the fact that some energy appears to be absorbed during the fermentation process.  Don’t worry though, the number is very low.

Now that you know that both soluble and insoluble fiber are good for you, aim to get your 25 or more grams per day.  A variety of fiber supplements are also available if you need a little help to get there from time to time.

To sum it up, fiber is an indigestible component found in plants. We should get at least 25 grams of fiber each day. Soluble fiber ferments as it passes, aids in digestion, and makes you feel full while insoluble fiber does not change as it passes and keeps you regular. Now you know the difference between soluble and insoluble fiber.

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