Advances in dietary fibre characterisation. 1. Definition of dietary fibre, physiological relevance, health benefits and analytical aspects.

Since 1953, the definition of 'dietary fibre' (DF) has evolved significantly following an international debate based on analytical progress, new nutritional and physiological knowledge and also private interests of the food industry. The overall tendency is towards an extension of the definition by including resistant starches as well as non-digestible oligosaccharides. This broadened definition is indeed based on physiological considerations as these compounds are not digested in the small intestine and become substrates for the colonic microflora, resulting in fermentation products that have a variety of local and possibly also systemic effects. A main reluctance to use this definition, however, is linked to the difficulty to quantify, with a universal method, the various compounds that fulfil the characteristics defined by this broad definition. At this point, if such a definition were adopted, there are two options, not necessarily antagonistic, which would be (1) to sum the content of NSP, resistant starches and non-digestible oligosaccharides quantified by distinct methods or (2) to use the Association of Official Analytical Chemists (AOAC) method of DF analysis (AOAC 985.29, 991.43) with complementary analyses of the different non-digestible oligosaccharides likely to be present in the food. With none of these solutions being fully satisfying from a scientific but also from a practical point of view, an innovative method has to be proposed within the next decade. The present review describes the various types of DF, effects of DF consumption on physiology and metabolism, past and current definitions, analytical aspects to measure DF and some aspects of DF claims and food labelling.