What is Fibre?

See also: What is Fat?

Fibre (fiber in the U.S.) comes exclusively from plants; there is no fibre in meat, fish or animal products (including dairy).

Fibre is a complex carbohydrate (type of sugar) but unlike other carbohydrates, which are broken down by the body to provide fuel in the form of glucose, fibre cannot be digested by the human body.

See our page: What are Carbohydrates? for more information.

We gain no nutrients or energy from fibre, it holds no calories as it is not digested, but passes through our digestive systems.

Fibre or ‘roughage’ does, however, provide an important function in the body; it is essential to a well-tuned digestive system and can help the body remove potentially harmful waste.

Nutritionists usually recommend that people increase their intake of high fibre foods. Studies have shown that most western diets contain only about half the recommended fibre.

The Benefits of Fibre Include:

  • High fibre foods help to fill you up. Fibre is bulky and takes up space in our stomachs, making us feel full and leaving less room for other foods containing calories. This can be helpful if you are trying to reduce your calorie intake and lose or maintain weight.
  • Foods that are high in fibre keep you feeling fuller for longer. It takes the body longer to process fibre and move it through the digestive system. This means your stomach stays fuller for longer after eating high fibre foods.
  • Fibre is well known for sustaining regular bowel movements and helping to prevent constipation as it stimulates the digestive system.
  • Fibre is useful for maintaining healthy colon function and high fibre diets may help prevent colon and other types of cancer.
  • People who eat a lot of fibre are more likely to be slimmer and less likely to put weight on than those who eat less fibre.

Types of Fibre

There are two main types of fibre - soluble and insoluble - both are beneficial to health.

Soluble Fibre

Soluble fibre dissolves in the stomach creating a sticky gel-like substance – a type of glue. This ‘glue’ traps certain components of food, fats and sugars, making them more difficult for the body to absorb.

This means that sugars (carbohydrates) are absorbed more slowly and blood sugar levels are kept steadier for longer.  Foods high in fibre and complex carbohydrates tend to have lower GI scores, sugars are released more slowly.

See the section about Glycaemic Index (GI) on our: Carbohydrates page for more information.

When soluble fibre dissolves it can also bind to certain fats in our stomachs. People who have high fibre diets are less likely to suffer from high cholesterol. Fibre can bind to and absorb cholesterol in the intestine before it can enter the bloodstream.  This is especially the case for low-density lipoproteins (LDL) the ‘bad’ cholesterol which, in high levels, can lead to serious health problems. People who want to lower their cholesterol are therefore advised to eat high fibre foods as well as reducing their intake of saturated and trans fats.

See our page: What is Fat? for more information.

Foods that contain good levels of soluble fibre include:

  • Oats and barley
  • Most beans and peas
  • Whole grains – as found in cereals and brown bread
  • Nuts and seeds
  • Fruit and vegetables

Insoluble Fibre

Insoluble Fibre does not dissolve in water or your stomach.

Rather it absorbs water and increases in size – as insoluble fibre passes through your digestive system it provides bulk and moisture to stools, a natural laxative effect, thus reducing the symptoms of constipation.  Bulkier stools are also helpful in cleaning the wall of the intestine removing wastes and promoting a healthy colon.

People who suffer from Irritable Bowel Syndrome (IBS) should be cautious about eating foods high in insoluble fibre on an empty stomach.  Although insoluble fibre is important to a healthy diet it may trigger symptoms of IBS, it is therefore recommended that sufferers mix high insoluble fibre foods with other less fibrous foods to minimise problems.

Foods that contain good levels of insoluble fibre include:

  • Whole grain wheat – as it includes bran
  • Corn (including popcorn)
  • Oats and oat bran
  • Nuts
  • Fruit and vegetables (especially the skins).


Bran is the hard outer layer of cereals including wheat, barley, oats and rice.

As the name indicates 'whole grain' foods contain the whole grain including the bran. Processed foods often include grains that have had the outer casing (bran) removed.  Such foods, like white bread, have less nutritional value than whole-wheat or wholemeal alternatives as they hold less fibre. To increase your fibre choose brown, granary or seed breads, brown rice and brown pasta.

Bran is also known for containing many essential fatty acids that are vital to health and can aid digestion.

See Fibre in Action

Make some porridge (oatmeal cereal)

Porridge is a popular, inexpensive and healthy breakfast dish. Making oat porridge is a simple experiment that demonstrates how fibre works in the body.

Ingredients: 1 part rolled oats to 2 parts liquid (milk, water or a combination).

Make porridge by heating up the ingredients to boiling point and then simmering until the desired consistency is reached. (The easiest way is in the microwave to avoid burning and sticky saucepans).

Oats are a good source of fibre (both soluble and insoluble).

When liquid is added to the oats they immediately start to grow – absorbing the liquid. As the liquid is heated the absorption rate increases, this is, in part, the action of the insoluble fibre adding bulk and moisture to the porridge.  As the porridge continues to cook the oats swell more – porridge can easily boil over, more than doubling in size while cooking, so keep an eye on it!

When cooked, the porridge has changed dramatically, you should notice two differences:

  • The oats have taken on a lot of moisture increased significantly in bulk – this is the action of the insoluble fibre.
  • The consistency of the porridge is a gloopy and somewhat sticky – the soluble fibre has dissolved to create this sticky (viscous) substance.

Finished porridge is quite bland - enjoy it with a some dried or fresh fruit, cinnamon, honey or a little added sugar, golden syrup or a pinch of salt.


One common side-effect of eating a fibre rich diet is flatulence or farting. Although humans cannot digest fibre, the bacteria present in our intestine and colon can - at least to some extent.

The by-product of the bacterial digestion of fibre is gas.  Levels of bacteria and their ability to digest different types of fibre vary in different people and at different times, this is why some people are more likely to suffer from flatulence than others.

In Summary

It is a well-known fact that fibre plays an important part in a healthy diet.

Although we gain no energy or nutrients from fibre, as we cannot digest it, it helps to keep our digestive systems healthy and can have other beneficial effects – like lowering cholesterol and reducing the risk of certain cancers. Furthermore high fibre foods make us feel fuller for longer and can therefore be useful for weight loss.