Marbling Matters: Lean and Fatty Red Meat Show Opposing Associations with Brain Structural Indices

Background/Objectives: Red meat is often treated as a single dietary category in nutritional epidemiology, despite substantial heterogeneity in fat content, quality parameters, and preparation methods. This may obscure meaningful associations with brain aging. We tested whether global brain structural associations differed across lean red meat, fatty red meat, pork, processed pork, and organ meat in a large community-based neuroimaging cohort. Methods: Participants were 45,811 UK Biobank adults aged 50 to 80 years with structural MRI, dietary recall, and covariate data. Dietary intake was assessed using up to five administrations of the Oxford WebQ 24 h recall and averaged across available timepoints. Global cortical thickness, total gray matter volume, and total white matter volume were derived from T1-weighted MRI. Continuous predictors were screened for linear quadratic, or spline form prior to grouped penalized variable selection. Final multivariable models incorporated sensitivity analyses stratified by socioeconomic status (SES) and sex. Results: Associations with global brain structure differed by meat type and fat content. Lean red meat showed the most favorable overall pattern, including modest nonlinear favorable association with global cortical thickness and a positive association with white matter volume among higher-SES participants. Fatty red meat showed unfavorable associations with cortical thickness and gray matter volume. Pork showed an unfavorable association with cortical thickness. Organ meat showed an unfavorable association with gray matter volume and with white matter volume among lower-SES participants. Overall, findings suggested that lean red meat tracked with neutral-to-favorable brain structural correlates, whereas fattier red meat and organ meat generally tracked with less favorable structural outcomes. Conclusions: Meat did not relate to global brain structure as a single uniform exposure. Instead, associations differed meaningfully by meat type, fat content, and socioeconomic context. Treating red meat as a single undifferentiated exposure may flatten biologically relevant heterogeneity and contribute to mixed prior findings. These results support more precise dietary phenotyping in brain-health research and suggest that distinctions in meat quality may matter when evaluating long-term brain aging. Findings should not be interpreted to suggest that unlimited meat intake is broadly health-promoting, even if lean, given the established cardiometabolic and vascular risks associated with excess intake of high-fat or processed meats.