The association of protein and carbohydrate intake with successful aging: a combined analysis of two epidemiological studies

Purpose: Previous studies have reported associations between levels of protein and carbohydrate intake with several health outcomes. Yet, their effect on successful (or healthy) aging remains unknown. The purpose of the present work was to investigate the association of protein and carbohydrate intake levels with successful aging. Methods: A cross-sectional analysis was carried out on the participants of two epidemiological studies; the ATTICA and the MEDIS studies. Anthropometrical, clinical and socio-demographic characteristics, dietary habits, and lifestyle parameters were derived through standard procedures. Successful aging was evaluated using a validated index (SAI) composed of 10 health-related social, lifestyle and clinical characteristics. Results: SAI levels were lower in low protein—high carbohydrate diet group (B = − 0.08, p = 0.04), but higher in high protein—high carbohydrate group (B = 0.06, p = 0.04), as compared to low protein and low carbohydrate diet, in participants living in insular areas. Protein—carbohydrate diet was not associated with SAI (all p’s > 0.05) among participants living in urban areas (p for diet—study interaction < 0.001). Conclusions: A high protein diet seems to be beneficial for older islanders in terms of successful aging; stating a hypothesis for a potential diet–environmental interaction that may be related to the quality of foods consumed and, consequently the sources of nutrients.