Dietary fibre

Key points

• Dietary fibre is found mainly in cereal foods, beans, lentils, fruit and vegetables.
• Dietary fibre can not be broken down by human digestive enzymes, although micro-organisms that live in the large intestine are able to digest fibre.
• Dietary fibre promotes a number of physiological effects, such as helping to prevent constipation, and helping to lower blood cholesterol and/or glucose levels.
• In the UK most people do not eat enough fibre (the average intake is 12g per day). The recommended intake for adults is currently 18g per day.
• A low fibre intake is associated with constipation and some gut diseases.
• Foods and food products that contain 6g fibre per 100g or 100 ml may be labeled as a ‘high fibre’ food.

What Is Dietary Fibre?
Dietary fibre used to be known as ‘roughage’.  It comprises the edible parts of plants that are not broken down and absorbed in the human small intestine. Types of dietary fibre may also be categorised according to their physiological effects; helping to prevent constipation or helping to control blood cholesterol and glucose levels. 

There are two broad types of fibre: insoluble and soluble. Oats, fruit, vegetables and pulses (beans, lentils, chickpeas) are good sources of soluble fibre.  Wholegrain cereals  and wholemeal bread are particularly good sources of insoluble fibre.  Because insoluble and soluble fibre are found in different proportions in fibre-containing foods and have different properties, it is important to eat a variety of fibre-containing foods.

Health Benefits of Eating Fibre
Both soluble and insoluble dietary fibre can promote a number of positive physiological effects, helping to prevent constipation, lower blood cholesterol levels and control blood glucose levels. Sources of insoluble fibre can act as bulking (laxative) agents and help prevent constipation.  For fibre to have the best effect on preventing constipation, an increase in fibre intake should be accompanied by an increase in water intake.  Soluble forms of fibre eaten in large amounts can help reduce blood cholesterol levels. They can also help people with diabetes to control their blood glucose levels.

How Much Fibre Do We Eat?
Most people do not eat enough dietary fibre. The average intake in Britain is 12g per day and it has been recommended that this rises to an average of 18g per day for adults. Children need proportionally less. For preschool children however, introduction of fibre-rich foods should be done gradually. Too much fibre can make the diet so bulky that young children become full before they have eaten sufficient food to satisfy their need for essential vitamins, minerals and energy. The major sources of dietary fibre in the British diet are whole-grain and high-fibre breakfast cereals and bread (because they are rich in fibre and are eaten frequently).

Fibre On The Label
Although there is no UK legislation covering fibre claims, the FSA has issued guidance notes. It recommends that a ‘source’ of fibre should contain 3g per 100g (or per 100ml) or at least 3g in the ‘reasonable expected daily intake of the food’ – i.e. the amount that could reasonably be expected to be eaten in one day. If the food is naturally high in fibre, the claim must take the form ‘a high fibre food’. For a claim of high fibre the food must contain at least 6g per 100g (or per 100ml) or at least 6g in the reasonable expected daily intake of the food.

© British Nutrition Foundation