Mediterranean Diet Adherence and Cognitive Function in Older Adults: Heterogeneity in the Association Across BMI Categories

Cognitive decline is a major public health concern among older adults, and both dietary quality and adiposity have been associated with cognitive health. Using data from the 2011-2014 National Health and Nutrition Examination Survey, we conducted a cross-sectional analysis of 2492 U.S. adults aged ≥ 60 years. Adherence to the Mediterranean diet was quantified using the Mediterranean diet index (MEDI) derived from two 24-h dietary recalls, and body mass index (BMI) was classified into four categories: underweight, normal weight, overweight, and obesity. Global cognitive function was computed by standardizing and summing scores from the Consortium to Establish a Registry for Alzheimer's disease immediate and delayed recall tests, the animal fluency test, and the Digit Symbol Substitution test. After multivariable adjustment, higher MEDI scores were associated with better global cognitive function, with positive associations also observed for verbal fluency and processing speed. Restricted cubic spline analysis supported a positive, approximately linear dose-response association between MEDI score and global cognitive function. However, in the linear interaction analysis, this association differed across BMI categories. Among normal-weight participants, higher MEDI scores were associated with better global cognitive function. Underweight status was associated with poorer immediate and delayed recall, whereas overweight status was associated with lower verbal fluency. Overall, greater adherence to a Mediterranean dietary pattern was associated with better cognitive performance, particularly verbal fluency and processing speed, among older U.S. adults. BMI-related heterogeneity in this association supports prospective longitudinal studies and intervention trials incorporating repeated assessments of diet, adiposity, metabolic health, and cognition.