Stable Isotope Values in Human Dentine Collagen and Fingernails Reveal Age‐Related and Socioeconomic Dietary Patterns in Brazil

ABSTRACT Objectives In this study, we analyzed δ 13 C and δ 15 N values in dentine collagen (reflecting early‐life diet) and fingernail keratin (reflecting recent diet) from 92 living adult individuals, having 75 individuals having paired dentine and fingernail samples available, across Brazilian regions with contrasting socioeconomic conditions. While the sample size was necessarily limited by the availability of paired tissues, it provides a unique dataset for assessing dietary change within the lifespan and its relationship to socioeconomic context. Materials and Methods Using Bayesian linear models and self‐reported dietary intake questionnaires, we investigated the influence of age, geographic region, and socioeconomic status on isotopic composition. Results We found significant regional and socioeconomic effects: individuals from high‐Human Development Index (HDI) municipalities and those reporting greater sugar intake had elevated δ 13 C values, while frequent fish and seafood consumption was associated with higher δ 15 N. Notably, δ 15 N in dentine collagen declined with tooth age, suggesting a historical decrease in the δ 15 N of food sources, likely linked to increased reliance on synthetic fertilizers and nitrogen‐fixing crops. Discussion Both tissues show a consistent regional contrast: participants from the Southeast exhibit higher δ 13 C and lower δ 15 N than those from the Northeast, consistent with greater intake of C 4 ‐derived, corn‐ and sugar‐based processed foods (“supermarket diet”’) and proportionally lower trophic‐level protein in the Southeast, versus lower δ 13 C in the Northeast consistent with diets centered on C 3 staples (rice, beans, manioc) and more limited access to ultra‐processed foods.