oa Compound-Specific δ13C Profiling of Amino Acids in Scalp Hair and Fingernails Reveal Dietary Habit, Sex and Tissue Type

This study explores how compound-specific stable isotope analysis (CSIA) of individual amino acids (IAAs) in scalp hair and fingernail tissues can be used to distinguish dietary habits and biometric traits. Unlike bulk isotope analysis, which averages isotope values across all AAs in protein-rich tissues, CSIA offers a higher-resolution nutritional biomarker. Samples were collected from 35 healthy adults and d13C values of bulk and 11 IAAs were measured. Multivariate statistical analysis (PCA, MANOVA, and CDA) revealed that AAs- Leucine, Valine, Isoleucine, Phenylalanine, and Tyrosine were key contributors to variation across all samples. Diet had strongest effect on d13C values of essential AAs, accounting for 74% of variance in hair and 62% in nails, while sex differences were more evident in d13C values of aromatic AAs. A random forest classifier predicted dietary group with 80% accuracy and sex with 66% accuracy. Additionally, hair and nail tissues exhibited distinct isotope signatures for d13C values of bulk, Glycine and Tyrosine. The findings highlight potential of CSIA of IAAs for detecting dietary habits and distinguishing phenotypic traits. Future research will aim to refine understanding of how amino acids from diet are metabolized and incorporated into hair and nails, enhancing CSIA’s diagnostic utility in health science.