The IAEA is launching a new five-year Coordinated Research Project (CRP) that aims to optimize the use of natural abundance stable isotope ratios of carbon (13C/12C, hereafter the “CIR”) to assess added sugar intake in different populations. This is relevant in terms of the emerging evidence for the role of carbohydrate and free sugar intake in chronic disease, and the recent guidelines issued by the World Health Organization (WHO) which recommend restricting free sugar in the diet to less than 10%, or even 5% of total energy intake for additional health benefits.
In many countries, the intake of refined carbohydrates and cane sugar is high in both adults and children. A biomarker of cane sugar intake, for example, could offer very useful information in dietary surveys. It would allow the assessment of the association of added sugars with chronic disease, within the framework of body fat accumulation. Nevertheless, it has become clear in recent years, based on comparisons with the few established dietary intake biomarkers, that available self-reported dietary assessment approaches have limitations. Objective biochemical measurements provide a useful approach to characterizing dietary exposures; however, to be acceptable for scientific use, the objective measure must provide a suitably accurate estimate of intake variation in study populations.
The natural abundance carbon isotope ratio (CIR, 13C/12C) has great potential as a biomarker for sugar intake due to the elevated CIR characteristic of sugar cane. Worldwide, there are many countries for which cane sugar is the predominant source of free sugars and for which corn is not a major component of either processed foods or animal feeds. In those countries, the CIR is likely to have higher validity and specificity as a biomarker of added sugar intake. The specificity of the CIR for added sugar intake can be improved when it is measured in molecules that favour the incorporation of glucose carbon, such as the amino acid alanine (CIR-ala). Studies in the USA have confirmed that CIR-ala has improved validity and specificity for free sugars/sugar sweetened beverage intake when compared with total CIR.
The CRP aims at testing the utility of total CIR and, if resources allow, CIR-ala as biomarkers of added sugar intake in adults, and to identify and gain knowledge of interfering dietary practices and other limitations. Therefore, adults from different populations outside the USA with different dietary backgrounds, including those who eat corn, millet or sorghum as staple food, will be assessed by comparing the biomarker with accurate measurements of the daily added sugar intake. The Doubly Labelled Water method will be used to validate the accuracy of the dietary recalls.
This CRP will comprise five to seven participating teams. Key elements required for the studies in this CRP will be the ability to recruit adult subjects with a range of habitual added sugar intakes, the ability to perform accurate and detailed dietary recalls, and the ability to collect urine samples and a single blood sample. The ability to work with stable isotopes, and the careful attention to detail in these studies will be critical. Finally, storage for sample aliquots and the ability to ship samples is important. Therefore, successful proposals will have to indicate the sources of added sugar, the range of added sugar intakes and potential dietary confounders (e.g. corn-fed animals), as well as the team’s experience with conducting dietary recalls and using isotope techniques.
