The carbon isotope ratio of alanine in red blood cells is a new candidate biomarker of sugar-sweetened beverage intake

Abstract

An objective dietary biomarker would help clarify the contribution of sugar-sweetened beverage (SSB) intake to obesity and chronic disease risk. Previous studies have proposed the carbon isotope ratio (δ13C) as a biomarker of SSB intake but found associations that were of modest size and confounded by other components of the diet. We investigated whether the δ13C values of nonessential amino acids (δ13CNEAA) in RBCs could provide valid biomarkers that are more specific to SSBs. We assessed the associations of RBC δ13CNEAA with SSB intake in a study population of 68 Yup'ik people, using gas chromatography/combustion/isotope ratio mass spectrometry to measure δ13CNEAA and four 24-h dietary recalls to assess intake. Among RBC nonessential amino acids, alanine δ13C (δ13Calanine) was strongly correlated with intake of SSBs, added sugar, and total sugar (r = 0.70, 0.59, and 0.57, respectively; P < 0.0001) but uncorrelated with other dietary sources of elevated δ13C. We also evaluated whether sweetener intake could be noninvasively assessed using hair δ13Calanine in a subset of the study population (n = 30). Hair δ13Calanine was correlated with RBC δ13Calanine (r = 0.65; P < 0.0001) and showed similar associations with SSB intake. These results show that δ13Calanine in RBCs provides a valid and specific biomarker of SSB intake for the Yup'ik population and suggest RBCs and hair δ13Calanine as candidate biomarkers of SSB intake for validation in the general U.S. population. Ultimately, these biomarkers could clarify our understanding of whether and how SSB intake contributes to chronic disease. © 2013 American Society for Nutrition.