(P13-032-24) Animal Protein and Related Intakes Associated With Plasma Carbon and Nitrogen Isotope Ratio Biomarkers in a Controlled Feeding Study of Postmenopausal Women

Objectives: Serum carbon and nitrogen isotope ratios (CIR and NIR, respectively) were previously shown to positively correlate with intakes of animal protein and food groups among women who participated in the Nutrition and Physical Activity Assessment Study Feeding Study (NPAAS-FS). We tested these correlations with intake using CIR and NIR measured in blood plasma.

Methods: The NPAAS-FS, an ancillary study of the Women’s Health Initiative (WHI), was a 2-wk, habitual intake controlled feeding study in postmenopausal women from the Seattle, WA area. We measured CIR and NIR in post-feeding serum and plasma samples from participants (n = 153) who completed the study. We calculated Pearson correlations between serum and plasma isotope ratios, and we determined correlations of plasma CIR and NIR with intakes of total animal protein (g/d) and related food groups to compare to correlations observed with serum isotope ratios. We also determined correlations with plant protein (g/d) and animal protein ratio (APR, animal/total protein). To be consistent with prior analyses, we excluded participants (n = 6) with unstable pre- and post-feeding serum isotope ratios.

Results: The correlations between plasma and serum measures were high for the CIR (r = 0.93, P < 0.0001) and NIR (r = 0.87, P < 0.0001). Associations of plasma CIR and NIR with animal protein and food groups were similar to those observed in serum. Animal protein correlated with both plasma CIR (r = 0.40, P < 0.0001) and NIR (r = 0.36, P < 0.0001). The food group most associated with plasma CIR was red meat (g/d) (r = 0.43, P < 0.0001), and the food group most associated with NIR was fish/seafood (g/d) ( r = 0.57, P < 0.0001). Plasma CIR and NIR were also negatively correlated with plant protein (r = -0.49, P < 0.0001 and r = -0.38, P < 0.0001, respectively). Accordingly, plasma CIR and NIR were more highly correlated with APR (r = 0.59, P < 0.0001 and r = 0.47, P < 0.0001, respectively) than total animal protein.

Conclusions: CIR and NIR associations with intake are consistent when measured in serum and plasma. These appear to be more explanatory biomarkers of APR, an energy-independent measure, than of animal protein intake alone. Next, we will develop a biomarker equation for APR and determine whether it can be used to calibrate intake and adjust disease-risk estimates in a larger WHI cohort.

Funding Sources: NCI, NHLBI