Stable carbon and nitrogen isotopes in whole blood as biomarkers of dietary patterns in a Brazilian population

Stable isotope analysis has become a valuable tool for reconstructing dietary patterns, but whole blood remains an underutilised matrix in these assessments. Therefore, this study investigates how δ¹³C and δ¹⁵N values in whole blood vary according to the frequency of consumption of different meat types in a Brazilian population and examines their associations with physiological and metabolic markers, including body mass index (BMI), cholesterol levels, and glutamic-oxaloacetic transaminase (GOT). Blood samples were collected from 287 individuals across 19 communities in Espírito Santo, Brazil, and analyzed for stable carbon and nitrogen isotope composition. Our findings indicate that higher beef, pork, and fish consumption was associated with enriched δ¹³C values, while both beef and fish consumption were associated with higher δ¹⁵N values. No significant isotopic differences were observed for chicken intake. δ¹³C values were positively associated with BMI and cholesterol levels in men but not in women, suggesting sex-specific metabolic influences on carbon isotopic fractionation. No significant associations were observed between δ¹⁵N and BMI or cholesterol levels, likely due to nitrogen turnover processes such as transamination and deamination. Additionally, a negative association between δ¹⁵N and GOT levels was identified, supporting the hypothesis that transamination may counteract nitrogen enrichment in blood, potentially limiting δ¹⁵N as a direct biomarker of protein intake. These results reinforce the applicability of stable isotope analysis for dietary assessment, demonstrating its potential to distinguish dietary patterns based on isotopic composition. They also highlight the influence of sex-specific metabolic processes on isotopic fractionation, underscoring the need for further research on nitrogen metabolism in dietary studies. This study provides novel insights into the role of stable isotopes in human nutrition and health research, contributing to the refinement of isotopic biomarkers for dietary and metabolic evaluations.