The association between dietary protein intake and mental disorders in older adults: a scoping review

Background Mental disorders are increasingly prevalent among older adults, significantly affecting their quality of life and overall wellbeing. Recent evidence suggests that dietary factors, particularly protein intake, may play a role in mental health outcomes. However, the association between dietary protein intake and mental disorders in older adults remains underexplored. This scoping review aims to examine the relationship between dietary protein intake and mental disorders among older adults. Methods This scoping review was conducted using the Preferred Reporting Items for Systematic Reviews and Meta-Analysis extension for Scoping Reviews (PRISMA-ScR). A comprehensive search was performed in three databases (PubMed, Scopus, and ProQuest Health) using predefined keywords and Boolean operators. The inclusion criteria and exclusion criteria were established. Thematic analysis was performed to synthesize and map the evidence across the included studies. Results From an initial 2,144 records, 13 articles ( n = 13) involving older adults were included. Three themes emerged from the thematic analysis: (1) Animal Protein; (2) Plant-Derived Protein; and (3) Mixed Proteins. Both animal and plant protein sources were examined, with generally favourable associations reported for cognitive health. However, findings were inconsistent, particularly for total protein intake, and varied according to protein source and mental or cognitive outcome. Discussion Associations between dietary protein intake and mental disorders in older populations are heavily dependent on specific protein sources and the synergistic whole-food matrix rather than the isolated protein quantity. While diverse high-quality protein consumption correlates with preserved mental health, the associations may concurrently reflect residual confounding from healthy-user biases and socioeconomic advantages. The cross-sectional design and lack of quality assessment limit causal inference. Thus, robust longitudinal research and targeted intervention studies are warranted to elucidate the independent neurobiological mechanisms of distinct dietary proteins from overarching dietary patterns.