Macronutrient energy ratios and cognitive health in older adults: A binational study of nonlinear associations and mortality links

Background The impact of dietary macronutrient composition on cognitive aging and Alzheimer's disease risk remains inadequately characterized. Objective To investigate the associations of carbohydrate, protein, and fat energy ratios with cognitive function and all-cause mortality among older adults in this binational study. Methods We analyzed data from the National Health and Nutrition Examination Survey (NHANES, 2011–2014; N = 2510) and the China Health and Nutrition Survey (CHNS, 1997–2006; N = 1600). Cognitive function was assessed using standardized composite z-scores. Associations were evaluated using weighted logistic regression (NHANES) and linear mixed-effects models (CHNS), with restricted cubic splines to examine nonlinearity. Cox models assessed mortality risk in NHANES. Results A higher carbohydrate ratio (CRC) exhibited a nonlinear inverse U-shaped association with the risk of cognitive impairment, with a significant threshold effect observed at approximately 48.5% of total energy intake. Moderate protein intake (PRC = 0.125–0.153, representing approximately 15% of energy from protein) was associated with the lowest risk of cognitive impairment in both cohorts. The fat ratio (FRC) demonstrated a complex nonlinear association, with cognitive risk increasing significantly when FRC fell below 33.2%. Lower CRC was associated with reduced all-cause mortality in the U.S. cohort (HRs for the lower quartiles: 0.68–0.72). Conclusions Modifiable macronutrient ratios are significantly associated with cognitive health and survival in older adults, with consistent findings across U.S. and Chinese populations. These results support dietary strategies that emphasize moderate carbohydrate intake (below approximately 48.5% of total energy) and balanced protein consumption (approximately 15% of energy) to promote cognitive health.