Dietary fibre is found in wholegrains, legumes, fruits and vegetables. Fibre is made up of the indigestible parts or compounds of plants, which pass relatively unchanged through our stomach and intestines. The main role of fibre is to keep the digestive system healthy. Other terms for dietary fibre include ‘bulk' and ‘roughage', which can be misleading since some forms of fibre are water soluble and aren't bulky or rough at all.
Fibre is largely a carbohydrate.The building blocks of all carbohydrates are different types of sugars and they can be classified according to how many sugar molecules are combined in the carbohydrate:
Dietary fibre is mainly needed to keep the digestive system healthy. It also contributes to other processes, such as stabilising glucose and cholesterol levels. In countries with traditionally high fibre diets, diseases such as bowel cancer, diabetes and coronary heart disease are much less common than in the West.
Many Australians don't consume enough fibre. On average, Australians consume 18-25g of fibre daily some far less. The Heart Foundation recommends that adults should consume approximately 30g daily. Australian experts suggest that children should eat 10g of fibre a day plus an additional gram for every year of age. For instance, a 10 year old child should eat 15-20g of fibre per day.
Disorders that can arise from a low fibre diet include:
Constipation
Irritable bowel syndrome
Diverticulitis
Heart disease
Some cancers including bowel cancer
Millions of doses of laxatives we swallow each year wouldn't be needed by most people if we ate more fibre. But getting everything working like clockwork isn't the only reason to check your fibre intake. A high-fibre diet also has a role to play in protecting us from heart disease and even some cancers.
Fibre is made up of a number of components of plant foods that aren't digested in the small intestine like other nutrients. However, fibre can be broken down to some extent by bacteria in the large intestine.
There are two main types: insoluble fibre and soluble fibre. A more recent addition to the fibre stable is resistant starch which, while not traditionally thought of as 'fibre', has been found to act in a similar way. All plant foods -- vegetables, fruit, legumes and grains -- contain a mixture of fibres, and each type plays an important role in the body.
Main types of fibre Insoluble fibre This is the type of fibre you probably first think of -- it's important to prevent constipation and associated problems like haemorrhoids. It works by providing bulk to the diet and speeds everything through the bowel. It can also have an influence on the bowel bacteria, which may help prevent bowel cancer.
This type of fibre has started to get a reputation for preventing heart disease. It's made up of things like pectin in fruit and gums in grains such as oats and barley, and legumes. It can lower cholesterol levels in the body and help with constipation, too. There's usually much more insoluble fibre in plant foods than soluble so if you're after a cholesterol-lowering effect, you need to take care to include high-soluble-fibre foods.
Starch is found in many plant foods and has always been thought to be completely digested by the body's normal digestive system. However, we now know that some starch doesn't get digested and ends up as food for bacteria in the large intestine. It's thought to act in a similar way to traditional fibre to improve bowel health. Resistant starch is in foods such as unprocessed cereals and grains, firm bananas, lentils, potatoes and especially in starchy foods that have been cooked then cooled (such as cold potatoes or rice). 'Hi-maize', added to foods such as some white breads and cereals, is also a type of resistant starch.
Most people only eat about two thirds of the fibre they need. At least 30 grams a day is the recommended amount for adults. Aim to get it from a variety of foods because each of the different types of fibre is important to different aspects of your overall health.
It's important that kids get enough fibre, although Australian guidelines don't specify an exact amount. The child's age plus 5 to 10 grams per day is a good amount to aim for.