Nutritional characterization and measurement of dietary carbohydrates

Abstract

Dietary carbohydrate characterization should reflect relevant nutritional and functional attributes, and be measured as chemically identified components. A nutritional classification based on these principles is presented, with a main grouping into 'available carbohydrates', which are digested and absorbed in the small intestine providing carbohydrates for metabolism, and 'resistant carbohydrates', which resist digestion in the small intestine or are poorly absorbed/metabolized. For the available carbohydrates, the chemical division into the starch and total sugars categories does not adequately reflect the physiological or nutritional attributes of foods. Characterizing carbohydrate release from starchy foods provides insight into some of the inherent mechanisms responsible for the varied metabolic effects. Also, a pragmatic approach to product signposting consistent with guidelines to limit free (or added) sugars is proposed. The most prominent of the resistant carbohydrates are the non-starch polysaccharides (NSP) from plant cell walls, which are characteristic of the largely unrefined plant foods that provide the evidence base for the definition and measurement of dietary fibre as 'intrinsic plant cell-wall polysaccharides' as proposed in conjunction with this paper and endorsed by the scientific update. Indigestibility in the small intestine was not considered to be an adequate basis for the definition of dietary fibre, as there is insufficient evidence to establish public health policy by this approach and concerns have been raised about potential detrimental effects of high intakes of rapidly fermentable resistant carbohydrates. Functional ingredients such as resistant starch and resistant oligosaccharides should therefore be researched and managed separately from dietary fibre, using specific health or function claims where appropriate. This structured approach to the characterization of nutritionally relevant features of dietary carbohydrates provides the basis for establishing population reference intakes, nutrition claims and food labelling that will assist the consumer with properly informed dietary choices.