The association between total, animal-based, and plant-based protein intake and cognitive decline in older adults

Objective: Epidemiological studies have suggested a potential cognitive benefit of higher protein intake, but findings have been inconsistent and inconclusive. This study examined associations of total, animal-, and plant-based protein intake and cognitive function and decline in older adults. Methods: Data were analysed from 1,339 community-dwelling adults aged 55 + (median age 65.2 y, IQR 61.0;72.1) participating in the Longitudinal Aging Study Amsterdam. Protein intake, measured via a Food Frequency Questionnaire (2014–2015), was expressed as energy percentage (%E) from total, animal-, and plant-based sources. Cognitive domains—global cognition (MMSE), information processing speed (Coding task), episodic memory (15WT), and executive function (Word Fluency)—were measured every three years between 2011 and 2021 and converted to z-scores. Linear mixed models evaluated associations between cognitive function and decline (testing interaction by age), adjusting for confounders including diet quality. Sex interactions were tested. Results: Mean protein intake was 1.1 g/kg/d (SD: 0.3). Higher quartiles of protein intake (%E) were associated with lower episodic memory (Q2–Q4 vs Q1, β_Q4 = − 0.18 (− 0.30; − 0.06)) and faster decline in global cognition (Q3 vs Q1, β = − 0.02 (− 0.03; − 0.00)) and processing speed (Q3 vs Q1, β = − 0.02 (− 0.03; − 0.01)). Results were comparable for total protein intake in g/adjusted kg/d. Animal-based protein intake was associated with faster decline in processing speed (Q3,Q4 vs Q1, β_Q4 = − 0.01 (− 0.02; − 0.00)). Plant-based protein intake was associated with higher processing speed in females only (Q4 vs Q1, β = 0.31 (0.09;0.53)) and lower episodic memory (Q4 vs Q1, β = − 0.16 (− 0.30; − 0.02)). No associations were found for executive function. Conclusion: These findings suggest protein intake does not benefit cognitive function in older adults. Negative associations may relate to protein food sources.