Objective biomarkers are needed to estimate dietary intake of added sugars if accurate associations with disease prevalence are to be generated.  The isotope ratio of carbon is a proposed biomarker as elevated 13C levels are found in both corn and cane sugar.  However, all plants using the C4 photosynthetic pathway have elevated 13C levels, and because animals consume these plants, it is not currently possible to discriminate between the dietary sources responsible for elevated levels of 13C.  Yun and colleagues conducted a study to determine if it was possible to differentiate between sugars and meat intake as the source of 13C.  The results of their study are published in the October 2020 issue of The Journal of Nutrition.

Samples for this work were collected from subjects in the Nutrition and Physical Activity Assessment Study Feeding Study of the Women’s Health Initiative.  The postmenopausal women (n=145) were provided diets for 2 weeks and fasting blood samples were collected at the beginning and end of the 2 week controlled feeding period.  The carbon isotope ratio of alanine, glycine, valine, leucine, isoleucine, proline and phenylalanine in blood were determined.

The carbon isotope ratio of alanine was associated (r= 0.32) with added sugar intake.  When a model of added sugar intake was developed using the carbon isotope ratios of alanine, glycine and isoleucine, as well as smoking, physical activity and body weight the criterion for serving as a biomarker was achieved (R2 = 0.37).  The biomarker was not associated with meat or animal protein intake.  The authors concluded that serum carbon isotope ratios of amino acids, when combined with participant characteristics, could serve as a biomarker of added sugar intake.

O’Connell states in a commentary on this article, that the outcomes of the Yun study further demonstrate the potential of carbon isotope ratios to predict long term added sugar intake from cane, but not beet sources.  O’Connell discusses two challenges associated with using carbon isotope ratios to estimate long term added sugar intake.  One is the issue of validation and the processes used to do so, as well as the issue of causal mechanisms responsible for circulating levels of 13C-amino acids.  O’Connell concludes by saying that the approach requires additional work to improve the technique, as it holds promise as a biomarker once appropriate validations are performed.

References Yun HY, Tinker LF, Neuhouser ML, Schoeller DA, Mossavar-Rahmani Y, Snetselaar LG, et al.  The carbon isotope ratios of serum amino acids in combination with participant characteristics can be used to estimate added sugar intake in a controlled feeding study of US postmenopausal women. The Journal of Nutrition, Volume 150, Issue 10, October 2020, Pages 2764–2771, https://doi.org/10.1093/jn/nxaa195.

O’Connell TC. Rough diamond:  A carbon isotope biomarker of added sugar intake.  The Journal of Nutrition, Volume 150, Issue 10, October 2020, Pages 2615–2616, https://doi.org/10.1093/jn/nxaa237.

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