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Dietary fibre

Key points

  • Dietary fibre is found in cereal foods, including bread, beans, lentils, fruit & vegetables
  • It cannot be broken down by human digestive enzymes
  • In the UK most people do not eat enough fibre (the average intake is 12.8g/day for women and 14.8g/day for men). The recommended average intake for adults is 18g (NSP) per day.
  • A low fibre intake is associated with constipation and some gut diseases such as bowel cancer
  • A high fibre diet can help reduce cholesterol, reduce the risk of diabetes and can help protect against overweight

What is dietary fibre?

Dietary fibre used to be known as ‘roughage’, and refers to a group of substances in plant foods which cannot be completely broken down by human digestive enzymes. This includes waxes, lignin and polysaccharides such as cellulose and pectin. Originally it was thought that dietary fibre was completely indigestible and did not provide any energy. It is now known that some fibre can be fermented in the large intestine by gut bacteria, producing short chain fatty acids and gases (methane, hydrogen and carbon dioxide). The fatty acids are absorbed into the blood stream and provide a small amount of energy. The amount of gas produced depends on the type of fibre eaten and the gut bacteria present. After a large increase in the amount of fibre in the diet, some people experience symptoms such as abdominal distension, discomfort and wind. However, the large intestine and gut bacteria gradually adapt to the increased intake and symptoms usually decrease.



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