Fibre effects on intestinal functions (diarrhoea, constipation and irritable bowel syndrome)

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Summary The effects of fibre on intestinal functions and diseases have been the area of a large body of research conducted over the past decades. In this presentation, some aspects of its effects on diarrhoea, constipation and its use in the irritable bowel syndrome (IBS) are discussed. Dietary fibre is difficult to define and difficult to analyse. Some studies on bowel function and intestinal disease have used high-fibre diets, while most have used fibre concentrates such as wheat bran or preparations of isolated non-digestible carbohydrates. Different fibre sources in the diet do not have the same qualitative or quantitative effects on intestinal functions, making general recommendations on fibre type and amount extremely difficult. Increased fibre intake will generally increase stool weight. The magnitude of the increase varies with the fibre source. The contributions of this increase from an elevated bacterial mass, faecal water and undigested fibre also vary markedly with the type of fibre. Data on the use of fibre are most convincing regarding constipation. Fibre increase bowel movement frequency modestly in constipation and improves symptoms. However, there is too little evidence to determine if one treatment is better than another, and to determine the best treatment for different types of patients, or what fibre source which is most effective. The use of fibre for the treatment of diarrhoea is poorly documented outside the area of enteral nutrition. Though effects have been shown, especially on the duration of diarrhoea in children, further research is needed for recommendations to be made. Fibre and bulking agents are commonly used in the treatment of IBS, but the benefits seem to remain unproven despite a large number of trials. Some IBS patients may benefit from fibre supplementation, but there are problems of tolerance in many patients. Some fibre products may be better tolerated than others, but data are too sparse for definite recommendations to be made.