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How to Understand the Difference Between Soluble and Insoluble Fiber

Fiber is an essential nutrient needed by the human body. Some of the benefits of fiber include the aiding of digestion and elimination of waste in the body, as well as helping control caloric intake. Fiber is considered a complex carbohydrate because it contains multiple linked glucose molecules. Because of the benefits of eating fiber when consumed with fats and other foods, the Institute of Medicine recommends consuming fiber at most meals. Many times food labels break down dietary fiber into two categories - soluble and insoluble fiber. Understanding the difference, and what each type of fiber does can make it easier when choosing foods based on fiber content.


  1. 1
    Define fiber by type. Total fiber, according to the Institute of Medicine, should be broken into two categories, functional fiber and dietary fiber.
    • Functional fiber is a carbohydrate that is not digested and has physiological health benefits, such as blood sugar stability. Functional fiber can come from plant or animal sources or it can be synthetic. Some examples of functional fiber are gums, pectins, polydextrose and inulin.
    • Dietary fiber is composed of a carbohydrate and lignin (non-carbohydrate or woody components of fruits or vegetables; cellulose is an example of a lignin) that are not digested by the body and are not used for energy. Dietary fiber is also known as roughage and helps with elimination of waste and the bulking of stools. Soluble and insoluble fiber are two categories of dietary fiber. The Institute of Medicine recommends 14 g of fiber per 1000 calories to get the maximum health benefits from fiber.
    • Soluble fiber is dietary fiber that will dissolve in liquid. It will form a gel in the body that has been linked to the slowing of fat absorption and the feeling of fullness. Some of the soluble fibers are more viscous than others and form thicker gels, which work very well at the slowing of fat absorption and the formation of fat to an extent. Some of the health benefits of soluble fiber are regulated blood glucose levels, lower LDL cholesterol, and lower risk of heart disease. With the exception of psyllium fiber, it does not have a laxative effect.
    • Insoluble fiber is dietary fiber that does not dissolve easily in liquid or form a gel. It does add bulk to stool to ease the passing of waste and it also helps food digest and pass through intestines and stomach quicker. Insoluble fiber has a laxative effect. Some health benefits of insoluble fiber include a lower risk of heart disease and regulation of caloric intake.
  2. 2
    Know what foods contain insoluble and soluble fiber. There are many foods that contain fiber, including all whole fruits and vegetables, but the amounts of insoluble and soluble fiber may vary. Since this information does not have to be listed on the nutrition facts panel it is useful to know keys foods containing each type of fiber.
    • Soluble fiber can be found in, but is not limited to, nuts, whole wheat flours, peas, oats, bran, citrus, apple, strawberry and barley.
    • Insoluble fiber can be found in, but is not limited to, cabbage, carrots, apple skin, beets, potato skin, whole wheat, sweet potatoes, turnips, brussel sprouts and cauliflower.
  3. 3
    Identify key components of food that contribute to soluble and insoluble fiber. Since many foods contain fiber, it is important to know the key attributes in a food that is high in fiber. Most foods containing fiber contain both soluble and insoluble fiber to certain degrees, with some having a higher degree of one fiber or the other.
    • The food is a whole grain, nut, legume or seed. These foods contain both soluble and insoluble fibers. Be sure to purchase 100% whole grain when buying ready to eat products. With whole grains, nuts or seeds it can be more beneficial to purchase these already ground because they are often harder for the body to digest completely, and, in order to get the benefit from the fiber, they must be small enough to participate in biochemical processes.
    • The food looks fibrous. Foods like sweet potatoes and carrots look very fibrous. This is good indication that the food is high in fiber.
    • The food is a whole fruit or vegetable. Processed fruits and vegetables tend to retain soluble nutrients, but lose the fiber. The best way to get the fiber from fruits and vegetables is to eat them whole. They don’t have to be raw and frozen whole vegetables work just as well as fresh.
    • The food becomes soft and creates a “sauce” when cooked. Foods like beans, oats and rice contain starch and fiber that are responsible for the creamy consistency. This is a good indication the food will be high in soluble fiber.
    • The food is a fruit, vegetable or whole grain and does not dissolve readily in your mouth. A good example of this is potato skin; it is edible, but requires extra chewing. The same is true for many fruits, like pears and apples. This is a good indication the food contains fair amounts of insoluble fiber.
    • Many processed foods have added fiber, either to replace what was lost during processing or add extra health benefits. If these foods do not state added fiber on the label, check the nutrition facts panel and ingredient statement to find out. The food should contain 1 or more g of dietary fiber. This can be naturally occurring or it can be added. The added fiber is considered functional fiber, but may also be classified as dietary fiber. Some of the added fibers, that are mostly soluble, are cellulose, gums (guar gum, carrageenan, etc.), inulin, and pectin. Some of the added fibers, that are mostly insoluble, are polydextrose and bran.

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    • Following a balanced diet rich in fruits, vegetables and whole grains will provide all the necessary fiber for a day.
    • Psyllium fiber, a common fiber supplement sold under the brand name Metamucil, is 70% soluble fiber and 30% insoluble fiber and has the health benefits of both types of dietary fiber.


    • The Institute of Medicine has recommended moving away from the terms soluble and insoluble for fiber, and, instead, using fermentability and viscous to describe the different types of dietary fiber. Nutritionists feel that measuring these instead of solubility gives a more accurate portrayal of the health benefits of fiber by category.
    • Too much fiber in the diet can cause bloating and gas, and it may interact with certain medications. Be sure to check with a doctor before taking fiber supplements or consuming a higher than recommended amount of fiber.

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    Español: entender la diferencia entre fibra soluble e insoluble, Italiano: Capire la Differenza tra le Fibre Solubili e Insolubili, Português: Entender a Diferença Entre Fibras Solúveis e Insolúveis, Русский: понимать разницу между растворимой и нерастворимой клетчаткой

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