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Soluble and insoluble fibre

It’s important to include a wide variety of foods in your diet in order to obtain a broad spectrum of different types of fibre.
Asparagus
© BBC Good Food

It’s important to include a wide variety of foods in your diet in order to obtain a broad spectrum of different types of fibre.

Let’s take a closer look at the various forms of fibre you might include in your diet.

Soluble fibres

First up, soluble types of fibre. These are the types that dissolve in water and become gel-like, they include:

Inulin

Found naturally in bananas, onions and asparagus, inulin slows digestion. It is not digested or absorbed in the stomach but reaches the bowel where it acts as food for the beneficial bacteria that live there. Inulin is known as a type of fructans (more on this later). Be aware that some people find this type of fibre upsets their system and causes them digestive discomfort.

Strawberries
Pectin is found in fruits like strawberries

Pectin

This is found in large amounts in fruits like strawberries and apples as well as vegetables like carrots and potatoes. Pectin fibres are well liked by our gut microbes! They can be helpful for managing cholesterol levels and because they delay stomach-emptying, they keep you feeling fuller for longer – helping to manage both your appetite and your blood sugar levels.

Insoluble fibres

Insoluble types of fibre, these cannot dissolve in water and include:

Cellulose

The main component of plant cell walls. When cellulose is eaten it passes unchanged through the gut, promoting the wave-like motion of the intestines. We call this movement peristalsis. It’s this muscular movement that drives food and waste through the digestive system. Legumes, nuts and wheat bran are all examples of foods that supply insoluble fibre.

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Sources of lignin include avocados

Lignin

Like cellulose, lignin forms part of the cell walls of plants. As the plant matures, the amount of lignin increases and the plant becomes tough and stringy. Think of the texture of older celery stalks or green beans – even after you boil them the tough, stringy texture is not broken down – this is lignin. Until recently it was thought that our gut bacteria couldn’t ferment lignin as well as other fibres. However, new research suggests gut bacteria can at least partially break down lignin, converting it into a fuel source they can benefit from. Sources include flaxseeds, whole grains, peas as well as avocados.

© BBC Good Food
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Fibre, Fermentation & the Gut with BBC Good Food

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