Fiber: Soluble vs Insoluble

Fiber: Soluble vs Insoluble

Fiber is a special type of carbohydrate which the body lacks the ability to digest. Though we do not absorb any calories from fiber, it is an important nutrient which aids in many bodily functions, specifically those in the digestive system. Fiber has been linked to a decreased risk of heart disease and some forms of cancer.

Fiber is found mostly in unprocessed foods such as fruits, vegetables and whole grains. With an increased prevalence of diets relying on ready to eat, convenience foods, many Americans do not get adequate amounts of this crucial nutrient. Though we look at fiber as a single nutrient, there are actually two different types, each with unique characteristics and benefits.

Soluble Fiber

Soluble fiber is soluble in water. Once it enters the digestive tract, it attracts water and turns into a gel. This slows down nutrient absorption which stabilizes blood sugar levels. Soluble fiber also lowers cholesterol, decreasing the risk of heart disease. Because soluble fiber absorbs excess water, it can alleviate diarrhea.

  • alleviates diarrhea
  • slows digestion
  • stabilizes blood sugar
  • softens stool
  • lowers cholesterol
  • sources: oats, barley, nuts, seeds, beans, lentils, peas and some fruits and vegetables

Insoluble Fiber

Insoluble fiber is not soluble in water. It adds bulk to the stool and decreases digestion time. Insoluble fiber acts as a natural laxative as it can alleviate constipation.

  • alleviates constipation
  • speeds up digestion
  • adds bulk to stool
  • sources: wheat bran, peels of fruit, vegetables and whole grains

Daily Fiber Intake

The Institute of Medicine makes recommendations for all nutrients based on gender, age and other health considerations such as pregnancy and lactation status. The current recommendation for daily fiber intake ranges from 19 grams per day for children to 38 grams per day for adult men.

  • Children: 19-25 grams per day
  • Males (age 9+): 30-38 g/d
  • Females (age 9+): 21-26 g/d
  • complete tables

The Bottom Line

Soluble and insoluble fiber are mainly found in unprocessed foods. With an increased consumption of processed and fast foods, fiber intake tends to nosedive. Fiber prevents cancer and heart disease, stabilizes blood sugar levels, treats diarrhea and constipation and increases satiety. These important health benefits make it imperative to consume a wide variety of foods high in fiber.


  1. Fiber. (2015, August 05). Retrieved March 13, 2016, from
  2. Fiber. (n.d.). Retrieved March 13, 2016, from
  3. Soluble vs. insoluble fiber: MedlinePlus Medical Encyclopedia. (2014, August 11). Retrieved March 13, 2016, from

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