Types of Fiber: Soluble and Insoluble Fiber

Medically Reviewed by Zilpah Sheikh, MD on January 17, 2024
6 min read

Fiber is a type of carbohydrate your body can't digest. We often think of fiber as the food that relieves constipation, but fiber has other health benefits as well. The two main types of dietary fiber are soluble fiber and insoluble fiber, but within each of those labels are many different kinds of this nutrient.

All types of soluble fibers slow digestion, so it takes longer for your body to absorb sugar (glucose) from the foods you eat. This helps prevent quick spikes in your blood sugar levels, which is an important part of managing diabetes. Soluble fibers also bind with fatty acids, flushing them out of the body and helping lower LDL (bad) cholesterol. Foods rich in this type of fiber include oatmeal, nuts, beans, apples, and blueberries.

Insoluble fibers help hydrate and move waste through your intestines. That helps prevent constipation, keeping you regular. Insoluble fiber is found in the seeds and skins of fruit (so always eat your peels). It is also found in whole wheat bread, brown rice, and leafy green vegetables such as kale.


This chart shows the most common types of dietary fiber and explains where they come from and how they can keep you healthy.

Types of FiberSoluble or InsolubleSourcesHealth Benefits
Cellulose, some hemicelluloseInsolubleNaturally found in nuts, whole wheat, whole grains, bran, seeds, edible brown rice, and skins of produce."Nature's laxative": Reduces constipation, lowers diverticulitis risk, and can help with weight loss.
Inulin oligofructoseSolubleExtracted from onions and byproducts of sugar production from beets or chicory root. Added to processed foods to boost fiber.May increase "good" bacteria in the gut and enhance immune function.
LigninInsolubleFound naturally in flax, rye, and some vegetables.Good for heart health and possibly immune function. Use caution if you have celiac disease or are gluten intolerant.
Mucilage, beta-glucansSolubleNaturally found in oats, oat bran, beans, peas, barley, flaxseed, berries, soybeans, bananas, oranges, apples, and carrots.Helps lower bad LDL cholesterol and reduces the risk of coronary heart disease and type 2 diabetes. Use caution if you have celiac disease or are gluten intolerant.
Pectin and gumsSoluble (some pectins can be insoluble)Naturally found in fruits, berries, and seeds. Also extracted from citrus peel and other plants. Boosts fiber in processed foods.Slows the passage of food through the intestinal GI tract and helps lower blood cholesterol.
Polydextrose polyolsSolubleAdded to processed foods as a bulking agent and sugar substitute. Made from dextrose, sorbitol, and citric acid.Adds bulk to stools and helps prevent constipation. May cause bloating or gas.
PsylliumSolubleExtracted from rushed seeds or husks of Plantago ovata plant. Used in supplements and fiber drinks and added to foods.Helps lower cholesterol and prevent constipation.
Resistant starchSolubleStarch in plant cell walls. Naturally found in unripened bananas, oatmeal, and legumes. Also extracted and added to processed foods to boost fiber.May help manage weight by increasing fullness. Helps control blood sugars, increases insulin sensitivity, and may reduce the risk of diabetes.
Wheat dextrinSolubleExtracted from wheat starch, and widely used to add fiber to processed foods.Helps lower cholesterol (LDL and total cholesterol) and may lower blood sugar and reduce the risk for heart disease; more research is needed. Avoid if you have celiac disease or are gluten intolerant.

The health benefits include:

Heart protection. Inside your digestive system, soluble fiber attaches to cholesterol particles and takes them out of the body, helping 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.

The health benefits include:

Weight loss. Like soluble fiber, insoluble fiber can play a key role in controlling weight by making you feel full.

Digestive health. Eating lots of insoluble fiber also helps keep 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, such as constipation, hemorrhoids, and fecal incontinence (problems controlling your bowel movements).

Generally, "prebiotic fiber" refers to a fiber that's a food source for the microorganisms in your gut. Fiber is nondigestible, so it makes its way to your colon more or less intact. There, microorganisms ferment it and use it as food, in the process creating short-chain fatty acids. These short-chain fatty acids can do things such as nourish colon cells and help produce mucus in your gut, which potentially protects against harmful compounds.

Prebiotics can also:

  • Help your body absorb calcium and phosphorus to improve bone density
  • Regulate your bowel movements
  • Improve your immune system's defense
  • Reduce the development of allergy-related diseases

Not every prebiotic will do all these things, as different microorganisms feed on different prebiotics. According to a study reported by the American Society for Nutrition, the foods with the greatest amounts of prebiotics per gram of food are:

  • Dandelion greens
  • Jerusalem artichokes
  • Garlic
  • Leeks
  • Onions

Other prebiotic-rich foods include onion rings, cowpeas, asparagus, and Kellogg’s All-Bran cereal, according to the study.

Most nutritionists suggest getting fiber from whole foods because they're healthy in other ways, too. Foods with fiber include fruits, vegetables, nuts, beans, and grains.

But if you don’t get enough from your diet, fiber supplements can help fill in the gap. "Functional" fiber is extracted from its natural sources and then added to supplements or fortified foods and drinks to boost their fiber content. Fiber supplements come in powders, capsules, or gummies.

Some of the most common ingredients in fiber supplements are:

  • Psyllium
  • Inulin
  • Wheat dextrin
  • Acacia gum
  • Calcium polycarbophil
  • Flaxseed
  • Methylcellulose
  • Arabinoxylan

A study found that taking too much inulin (30 grams) caused people to get a spike in body inflammation. However, one study participant reported decreased inflammation at this high dose. It seems that people may respond differently to different fiber supplement ingredients and amounts.

Only 5% of Americans get the recommended amount of fiber (around 30 grams) in their diets. The average American only gets about half of this amount daily. Research shows that low income is linked to low fiber intake. The chart below gives the daily fiber nutritional goals, according to the U.S. Department of Agriculture and U.S. Department of Health and Human Services' Dietary Guidelines for Americans, 2020-2025.

19-3028 grams34 grams
31-5025 grams31 grams
51 and older22 grams28 grams

While most people don't get enough fiber, it's possible to overdo it, especially if you're on a vegan or raw food diet. Eating too much fiber can cause:

  • Intestinal gas
  • Abdominal bloating
  • Abdominal cramping

To avoid these, increase the amount of fiber in your diet gradually, so your body gets used to it.

Most Americans don't eat enough fiber. Fiber is important for regular bowels, controlling weight, lowering cholesterol, and preventing spikes in blood sugar. You can get fiber from fruits, vegetables, oatmeal, beans, nuts, and seeds. Aim to eat a wide variety of fiber-rich foods.

Is there a difference between fiber and dietary fiber?

Yes, fiber is found in all plants. Dietary fiber is the fiber that you might eat but not be able to digest. It's a type of carbohydrate.

Which type of fiber is the best?

Both soluble and insoluble fibers are important. You should eat a variety of fruits, vegetables, whole grains, and nuts because different types of fibers are found in different foods.