Snapshot series 4: The dietary fibre

Dietary fibre is the indigestible component of foods and drinks which has a bulking effect in the large intestine and provides a substrate for the colonic bacteria. 

Originally, ‘fibre’ was limited to non-starch polysaccharides (such as cellulose) plus lignin from plants. In recent years the definition of fibre has widened to include all food components that are not digested and absorbed in the small intestine, including the non-digestible oligosaccharides (which are between the simple sugars and the starch polymers) and resistant starch. 

There  is also an increasing use of novel, synthetic f ibres in processed foods and drinks. Recent research suggests that a high intake of dietary fibre, particularly cereal fibre and whole  grains, is associated with a reduced risk of cardiometabolic disease and colorectal cancer. 

   Higher intakes of some fibre components are also associated with reductions in serum cholesterol and triacylglycerols as well as blood pressure. 

  As a result, in recent years many countries have raised the recommended intake of dietary fibre to 30 grams (1 oz) or more for adults  –  almost twice the average present intake. The novel fibres, such as polydextrose, are of potential benefit, but evidence is needed to show that they have beneficial effects in the people consuming them. 

Fibre is provided by cereals, legumes and fruit and vegetables. Reduced risk of cardiometabolic disease and colorectal cancer is particularly linked to high intakes of cereal f ibre and wholegrain foods.

 However, simply consuming greater quantities of the novel synthetic fibres should not be encouraged unless clear beneficial effects can be demonstrated (for example, stool bulk, appetite and reduction in serum lipids such as cholesterol.