The maintenance of gut health is complex and relies on a delicate balance between the diet, the commensal microflora and the mucosa, including the digestive epithelium and the overlying mucus layer. Superimposed on this balance is the frequent presence of enteric bacteria with pathogenic potential, the proliferation and metabolic activity of which may perturb digestive function, and lead to diarrhoea, poor growth rates and even death. Such enteric infections with pathogenic bacteria are common in young animals and children. Diet has an important influence on gut health, including effects on proliferation of pathogenic bacteria, and it can provide either beneficial or harmful input. Dietary fibre (DF) is a dietary component that has a major influence in this regard. DF is a heterogeneous class of components that are not hydrolysed by digestive enzymes of non-ruminant animals, and consequently are the main substrates for bacterial fermentation in the distal part of the gut. This review presents evidence that some components of dietary fibre may improve gut health, or alternatively enhance gut perturbation and subsequent diarrhoea in young animals (including piglets, chickens and children). This review reports and discusses how DF interacts with the gut epithelium and mucus, directly or by the way of the microflora, and consequently can protect against or enhance enteric infections. (C) 2003 Elsevier Science B.V. All rights reserved.