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

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 (δ¹³C_NEAA) in RBCs could provide valid biomarkers that are more specific to SSBs. We assessed the associations of RBC δ¹³C_NEAA with SSB intake in a study population of 68 Yup'ik people, using gas chromatography/combustion/isotope ratio mass spectrometry to measure δ¹³C_NEAA and four 24-h dietary recalls to assess intake. Among RBC nonessential amino acids, alanine δ¹³C (δ¹³C_alanine) 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 δ¹³C_alanine 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.