Fibre

Roles of fibre in the body

Fibre is not technically a nutrient as it is generally resistive to human digestive enzymes. Also known as non-starch polysaccharide or NSP it is not absorbed into the blood stream, however fibre still has important roles in the diet. Fibre absorbs water and therefore tends to fill us up, replacing high calorie foods in the diet. Recommended intake of fibre is around 30g/day. Fibre is found in the outer walls of grains and seeds, they make up the walls of vegetables and fruits. Unrefined foods are therefore higher in fibre than those that have been processed. Generally, people in the UK do not consume enough fibre in the diet. Too much fibre in the diet can lead to increased flatulence and abdominal discomfort. This may occur when increasing fibre intake too rapidly from a very lose base. High fibre diets can reduce the absorption of minerals, especially calcium, iron and zinc by binding to them, reducing the absorption and leading to deficiency. When increasing fibre intake it is important to increase the fluid intake as fibre absorbs fluid, which could lead to constipation.

Classification of fibre

Fibre can be classified into two types according to its solubility in water. These forms have different sources and benefits to health. Water soluble fibre is found in the fleshy part of fruit and vegetables, e.g. citrus fruits and apples, and may help to lower blood cholesterol and, therefore, reduce the risk of CHD. Common foods providing a good source of this type of fibre include oats, kidney beans and the pulp of fruits Water Insoluble is found in the woody, structural part of fruit and vegetables, grain products and bran. This type of fibre stimulates the muscles of the digestive tract preventing constipation, haemorrhoids and diverticulitis. It is also thought to reduce the risk of colon cancer by speeding up the passage of food through the colon. Sources include the skins of fruit/vegetables and outer coating of whole cereals.