Soluble and Insoluble Fiber: What You Need to Know

Two Types of Fiber That Have Big Benefits for Your Health

A close-up view of wheat.
A close-up view of wheat. Vadim Karpus/EyeEm/Getty Images

Fiber is important for everyone, but that's especially true if you have diabetes. That's because fiber can help with weight and blood sugar control. There are two main types of fiber—soluble and insoluble fiber—and they perform different functions in your body.

What Is Fiber?

Dietary fiber is the part of whole plant foods that your body can't break down. It helps you to feel full, helps keep your bowels regular, aids in pulling bad cholesterol out of the body, and helps you digest food more slowly, preventing spikes in blood sugar.

Fiber-rich whole foods can improve your nutrition, glucose tolerance, and blood fat profiles, reducing the risk of type 2 diabetes, cardiovascular disease, and obesity.

You'll also find that prepared foods may have added fiber—also called functional fiber. It is debatable as to whether it provides the same health benefits as fiber from natural plant sources, but certainly can't hurt.

Insoluble Fiber

Insoluble fiber is the kind that's bulky and doesn't dissolve in water. It speeds up the movement of food through the digestive system. Think of insoluble fiber as a scouring pad moving food through the digestive system and polishing your intestines as it goes through. This type of fiber acts as a laxative, preventing constipation.

You can find insoluble fiber in nuts, seeds, vegetables, and whole grains. Think of the woody or grassy surfaces of nuts and seeds, apple peels and the flecks of "whole grain" that you see in stone-ground flour. As a functional fiber, you might see it listed on food labels as cellulose.

Soluble Fiber

Soluble fiber dissolves in water but it does not break down completely. Instead it attracts water and turns into a gel-like substance that slows digestion. Soluble fiber comes from the part of the plant that stores water. It can form a gel such as mucilage, gum, or pectin. An example of this type of gel is the gooey inside of cactus pads or the thickened boiling water after you boil beans.

Soluble fiber slows your digestion by making it harder for your body to break down carbohydrates, convert them to glucose, and absorb glucose into your bloodstream. This helps prevent dramatic increases in blood sugar levels, which then helps insulin work better. This type of fiber also helps to block some fat absorption. Soluble fiber can help lower cholesterol, promote weight loss and reduce risk for stroke, diabetes, gastrointestinal disorders, heart disease, and some cancers. It also helps you to feel full and reduces cravings.

You can find soluble fiber in beans, citrus fruits, apples, carrots, barley, oats, flax seeds, and psyllium husks. On food labels, insoluble fiber might be listed as gum or pectin.

Fiber Recommendations

The 2015-2020 Dietary Guidelines for Americans bases their fiber recommendation on total calorie intake. It is recommended that American adults consume 14 g of fiber per 1,000 calories ingested. For example, if you consume about 2,000 calories per day, you should be eating 28 grams of fiber daily. If this is confusing, you can follow the position of the American Academy of Nutrition and Dietetics that states, woman should consume at least 25 grams of fiber per day and men 38 grams daily. Depending on age, children should consuming about 14 grams per day. The problem is that most Americans are falling short. The average American only gets around 17 grams per day, with only 5 percent of the population eating the Adequate Intake. 

Adding Fiber to Your Diet

Try to get the recommended amount of fiber, but don't go overboard. Too much fiber, or a lot of fiber when your body is not used to it, can be bad too, causing gas, bloating, diarrhea and cramps. If you're not used to eating much fiber, increase gradually, every few days. Try to eat small amounts throughout the day rather than getting a lot of fiber at one meal and drink plenty of water.

Some simple ways to start is: 

  • Aim to eat 3-5 servings of non starchy vegetables per day: 1/2 cup cooked, or 1 cup raw
  • Consume about two serving of fruits daily: high fiber choices include berries, apples, and pears
  • Choose whole grains, such as whole grain bread, oatmeal, ancient grains, such as quinoa, bulgar, barley, farro, millet, freekah, etc.
  • Eat unsalted nuts daily—one serving is 1/4 cup or one handful
  • Sprinkle some ground flax, hemp, or chia seed into your yogurt 
  • Toss some legumes, such as chickpeas into your salad for a protein and fiber boost
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