The Association of Amount and Source of Dietary Protein with Muscle Mass and Strength in Old Age

Abstract

Purpose Age-associated losses of muscle mass and strength are important predictors of disability in older persons. Although several mechanisms contribute to the decline in muscle mass and function seen with ageing, the process is accelerated by an inadequate protein intake (Cruz-Jentoft et al, 2019). However, the optimal amount and source of protein and the role of protein intake over the life course remain uncertain (Nishimura et al, 2023). In a sample of community-dwelling adults in Western Norway, the current study examined cross-sectional and longitudinal associations over 20 years of dietary protein intake with appendicular skeletal muscle mass (ASMM) and muscle strength measured by handgrip strength (HGS) in older age. Method Dietary intake was assessed using a paper-based food frequency questionnaire (FFQ) in middle age and a web-based FFQ in older age within the community-based Hordaland Health Study. ASMM was estimated by bioelectrical impedance analysis and HGS was measured using a handheld dynamometer. Results and Discussion Adjusted linear regression analyses revealed a negative cross-sectional association between the substitution of total protein and animal protein, with fat and carbohydrates, on ASMM in women. No longitudinal associations were found between substitution of dietary protein intake and ASMM in either sex. Similarly, no cross-sectional or longitudinal associations were evident between substitution of dietary protein intake and HGS in either sex. Notably, we did not find substitution of animal protein by plant protein to be associated with ASMM or HGS, suggesting that the source of protein may be less important, particularly when the requirement for total energy intake and total protein intake is fulfilled. This is highly relevant considering the predominantly plant-based diet promoted by emerging dietary recommendations, based on diet-health relationships and environmental sustainability concerns. Despite the general perception that older adults may benefit from an increased dietary protein intake, longitudinal evidence linking protein intake in midlife to muscle mass and function in older age is scarce. The current study is a valuable contribution to the knowledge on protein intake adequacy in older adults with high-functional capacity, which may have implications for policymakers establishing dietary recommendations (Sabir et al, 2024).