Dietary guidelines for sugar: the need for evidence

Within the area of public health nutrition, the dietary component arguably most in need of an evidence-based approach is sugar. Since the 1970s, when it was labelled ‘pure, white and deadly’ (Yudkin, 1972), and through the intervening years, when the ills of obesity, heart disease, hyperactivity, diabetes and Crohn’s disease were laid at its door, sugar has been the subject of much discussion and even controversy in the scientific community. As in the case of dietary fat, there are various types of sugar, e.g. sucrose, glucose, lactose and fructose. Unlike dietary fat, there is no accepted definition to categorise sugars, which makes comparisons between surveys and studies rather difficult (Kelly et al. 2003). While many countries express their intake data and dietary guidelines as ‘added sugars’, ‘total sugars’ or sucrose (for review, see Ruxton et al. 1999), the UK was unique in adopting the more complex definition of non-milk extrinsic sugars (NMES) (Committee on Medical Aspects of Food Policy, Department of Health, 1989). The aim of the definition was to differentiate between the array of simple sugars inherent in whole fruits and vegetables, and those of an identical chemical nature that are added to food or are naturally present in juices. The reasoning behind such a differentiation was that NMES were cariogenic, while milk sugars and those of an intrinsic nature had a negligible effect on teeth. However, the evidence supporting the classification of NMES and the selection of a quantitative guideline of 10 % food energy (Committee on Medical Aspects of Food Policy, Department of Health, 1991) have been questioned by some authors (Hussein et al. 1996; Ruxton et al. 1999; Kelly et al. 2003). In a controlled experiment to examine the justification for the NMES classification, Hussein et al. (1996) prepared samples of whole (representing intrinsic sugars) and homogenised and juiced (representing extrinsic sugars) fruits. Ten adult subjects were exposed to a 1 min rinse–chew of each preparation, after which samples of dental plaque were removed and tested for pH. The results were compared with a standard sucrose solution (100 g/l). Statistical analyses of both the minimum pH and the area under the curve demonstrated no significant difference between intrinsic and extrinsic sugars, except for minimum pH after rinsing with orange juice. The authors concluded that the acidogenic potential of intrinsic and extrinsic sugars derived from fruits was similar. The importance of this study was not the finding that intrinsic sugars are potentially cariogenic (in practice fruit consumption does not correlate with dental caries), but the serious questions it raises about the theory underpinning the NMES classification. Even if the NMES classification were scientifically supported, it is not easy to use in practice. There is currently no analytical method available to differentiate intrinsic from extrinsic sugars; thus, assumptions have to be made about the types of sugar present in food products, e.g. tinned fruits are assumed to contain 50 % extrinsic and 50 % intrinsic sugars (Ruxton et al. 1999). A less arbitrary way of defining dietary sugars would undoubtedly assist in designing studies to investigate their effects on health. Perversely, this creates a circular argument; in order to pin down scientifically the definition of sugars, a clear idea of the supposed problem is needed. For example, it is widely acknowledged that fruit is healthgiving (Department of Health, 1997), yet fruit contains glucose, sucrose and fructose that are chemically indistinguishable from those used to sweeten foods and beverages. This suggests that any adverse health effects of sugar cannot be due to their chemical composition but must relate to some other attribute of high-sugar foods. If this is the case, why the need for a quantitative guideline for sucrose? Quantitative guidelines infer that there is a cut-off point beyond which consumers increase or decrease their risk of disease. The widely accepted limits on dietary fat owe their existence to evidence, such as that reviewed by Committee on Medical Aspects of Food Policy, Department of Health (1994), that demonstrates a convincing relationship between cardiovascular disease risk and consumption of saturated fat. The quantitative guidelines for sugars adopted by a number of European countries, which range from 10–25 % food energy, have a rather less convincing foundation. The main reason cited for supporting an upper limit for sugar consumption is the desire to improve dental health, particularly amongst children. While fermentable sugars, such as sucrose, are undoubtedly cariogenic, the available evidence suggests that the deleterious effects of sugars relate to how frequently they are eaten as opposed to the actual quantity consumed per d (Stecksen-Blicks & Borssen, 1999; Tinanoff & Palmer, 2000). This is particularly true in groups of subjects where oral hygiene is poor and the ameliorating effects of fluoride are absent (Gibson & Williams, 1999). When the aetiology of caries is considered (Kandelman, 1997), it makes sense that the number of times that teeth are exposed to sugar should be the key dietary factor in the development of the disease. Such evidence has driven the consideration of dietary guidelines for sugar in some spheres (Arens, 1999; Institute of Medicine, 2002; World Health Organization/Food and Agriculture Organization, 2003) towards the adoption of British Journal of Nutrition (2003), 90, 245–247 DOI: 10.1079/BJN2003922 q The Author 2003