The lowdown on fibre

Health Hub staff
Wednesday, December 1, 2010
Low-down on fibre. Image: Getty
High-fibre foods also produce greater bulk in the stomach increasing the feeling of fullness (which is handy if weight is an issue).
Health Hub staff
Probably the best thing you can do to promote healthy bowels is eat a healthy diet which is high in fibre.

The best sources of fibre are plant foods: cereals (bread, rice and pasta), vegetables, legumes, fruit, nuts and seeds. These high-fibre foods give stools bulk, which helps you to pass them more easily.

While the physical presence of fibre in the bowel is important, there is extra value from dietary fibre. Dietary fibre can help slow the rate of digestion and help control blood sugar levels.

High-fibre foods also produce greater bulk in the stomach increasing the feeling of fullness (which is handy if weight is an issue) and, importantly when fibre and resistant starches reach the colon, they are broken down by bacteria.

During this process volatile fatty acids are produced. One of these — butyric acid — helps keep the cells in the walls of the colon healthy and may play a part in lowering your risk of bowel cancer.

What is dietary fibre?
Dietary fibre is defined as the remains of the edible part of plants and other carbohydrates that are not digested in the small intestine but pass to the large bowel where most are completely or partially broken down by bacteria.

Dietary fibres can be characterised as soluble or insoluble:

  • Soluble fibre slows the rate of digestion and absorption of food, and helps reduce cholesterol absorption. Soluble fibre is found mostly in oats, psyllium, barley, vegetables, lentils, beans and fruits.

  • Insoluble fibre maintains bowel regularity and helps keep you healthy on the inside. Insoluble fibre is found mostly in wheat bran, wheat-based cereals and pasta and wholemeal and wholegrain bread.

Resistant starch
Resistant starch also has an important role in bowel health by contributing to stool bulk and production of volatile fatty acids. In fact there is good evidence to indicate fermentation of resistant starch in the large bowel may produce much greater quantities of valuable volatile fatty acids than dietary fibre. But whether starches are digested in the small or large intestine depends on a number of complex structural factors.

The way food is prepared may also alter the site where starches are broken down. For example, the starch in a hot potato is digested by enzymes in the small intestine whereas the starch in the same potato allowed to cool, alters its structural alignment and resists being broken down by enzymes, so it passes instead to the large bowel as "resistant starch".

You can ensure your body receives all the fibre and resistant starch it needs by eating a healthy diet which contains foods high in fibre from a variety of sources.

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