What's The Difference Between Soluble and Insoluble Fibre?

RNDr. Tomáš Novotný
RNDr. Tomáš Novotný
31 Oct 2024
Reviewed by Mgr. Kristýna Kovářová
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What's The Difference Between Soluble and Insoluble Fibre?
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  • Fibres are categorised into two types based on their behaviour in water: soluble and insoluble.
  • Soluble fibre forms a viscous gel when combined with water, while insoluble fibre also binds water but does not dissolve.
  • Consuming both types of fibre offers various health benefits.

Fibre is sometimes an overlooked aspect of nutrition, yet adequate intake has been shown to lower cholesterol, promote satiety, and support prebiotic functions. Higher fibre intake also has a protective effect against colorectal cancer.

Fibre is a heterogeneous group composed of various indigestible oligo- and polysaccharides. Based on their solubility, they are classified as either soluble or insoluble. While both types benefit the body, they exhibit distinct properties within the digestive tract.

Fibre and its types

Fibre refers to oligo- and polysaccharides that are neither digested nor absorbed in the small intestine, allowing them to pass unchanged to the large intestine. There, they are metabolised by the intestinal microflora to form simple organic acids. The recommended daily fibre intake for adults is at least 25g. However, for individuals with higher energy needs, such as athletes, fibre intake can be up to twice as high.

How much fibre per day?

EFSA, 2010WHO, 2023DACH, 2021
25g per day> 25g per day> 30g/day
(> 14.6g/1000 kcal)

Dietary fibre is a heterogeneous mixture of various oligo- and polysaccharides that meet the criteria of indigestibility. These include beta‑glucans, resistant oligosaccharides, and resistant starches. For simplicity, fibre is divided into two groups: soluble and insoluble. Although they differ in physical properties, both types have unique effects on the human body.

Soluble fibre

Soluble fibre binds the water present in the digestive tract and dissolves to form a viscous gel. This gel passes through the small intestine and is fermented by intestinal microflora in the large intestine.

Probiotic microorganisms metabolise soluble fibre to produce short‑chain fatty acids (SCFAs), which are then absorbed into the bloodstream. This process increases satiety after meals and reduces the glycaemic response, thus having a positive effect on insulin sensitivity and generally exerting a protective effect against the development of type 2 diabetes.

In addition to short‑chain fatty acids, lactic acid formation also occurs, which lowers the pH in the colon. This environment selectively promotes the growth of beneficial microorganisms such as Lactobacillus and Bifidobacterium.

Soluble fibre in food

Soluble fibre constitutes roughly one‑third of daily fibre intake but plays a vital role in prebiotic function. Common sources of soluble fibre include:

  • Pectin‑rich foods, such as fruits, vegetables, and potatoes
  • Vegetable gums used as thickeners (e.g., carrageenan, guar gum, xanthan gum)
  • Resistant oligosaccharides, including fructooligosaccharides (FOS) and galactooligosaccharides (GOS)
  • Hemicellulose, particularly arabinoxylan, which is found in sources like psyllium
What's The Difference Between Soluble and Insoluble Fibre?

Insoluble fibre

Insoluble fibre does not dissolve in water but can bind to it, increasing its volume in the digestive tract. Like soluble fibre, it passes through the small intestine unchanged. However, it is not absorbed in the large intestine and is eventually excreted in the stool.

Insoluble fibre accelerates the passage of digestive material through the digestive tract, supporting healthy intestinal peristalsis and regular bowel movements. To avoid constipation, ensure you’re drinking enough water, as insufficient hydration can counteract the benefits of insoluble fibre.

Insoluble fibre in food

Insoluble fibre makes up a significant portion of daily dietary fibre intake. It is commonly found in nuts, seeds, legumes, whole grains, and the skins of fruits and vegetables. Key sources include:

  • Cellulose – found in vegetable skins and whole grains
  • Resistant starch – present in potatoes, corn, and tapioca flour
  • Lignin – a polysaccharide in woody plants, though it is less common in human nutrition

Bottom line

Fibre is an essential yet often overlooked nutrient. It provides numerous health benefits, from lowering cholesterol to promoting regular bowel movements, and its prebiotic properties help nourish the gut microflora.

Fibre is typically divided into two types: soluble and insoluble. Soluble fibre forms a viscous gel in the digestive tract and serves as food for the gut microflora, which then produces short‑chain fatty acids. These acids help reduce the glycaemic response and increase satiety.

Insoluble fibre acts as a "brush" for the intestines, supporting peristalsis. Like soluble fibre, it binds water in the digestive tract, further enhancing satiety.

RNDr. Tomáš Novotný
RNDr. Tomáš Novotný
Author
RNDr. Tomáš Novotný

A trained chemist who specializes in nutrition and the production of food and supplements. He works as a production manager at Aktin and is involved in the development of dietary supplements.

RNDr. Tomáš Novotný
RNDr. Tomáš Novotný
Author
RNDr. Tomáš Novotný

A trained chemist who specializes in nutrition and the production of food and supplements. He works as a production manager at Aktin and is involved in the development of dietary supplements.

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