The Association of Isocaloric Substitution of Dietary Protein in Middle Age with Muscle Mass and Strength in Old Age: The Hordaland Health Study

Background: Age-associated loss of muscle mass and strength is an important predictor of disability in older persons. Although several mechanisms contribute to the decline in muscle mass and function seen with aging, the process is thought to be accelerated by an inadequate protein intake. However, the optimal amount and source of protein and the role of dietary protein intake over the life course remain uncertain.Objectives: In a sample of community-dwelling adults in Western Norway, the current study examined both cross-sectional and longitudinal associations over 20 y of dietary protein intake with appendicular skeletal muscle mass (ASMM) and muscle strength measured by handgrip strength (HGS) in older age.Methods: Dietary intake was assessed using food frequency questionnaires (FFQs) in middle age (46-49 y) and older age (67-70 y) within the community-based Hordaland Health Study.Results: Adjusted, multivariate linear regression analyses revealed a negative cross-sectional association between the substitution of total protein (TP) and animal protein (AP), with fat and carbohydrates, on ASMM in women but not in men. No longitudinal associations were found between substitution of dietary protein intake and ASMM in either sex in adjusted models. Similarly, no cross-sectional or longi-tudinal associations were evident between substitution of dietary protein intake and HGS in either sex in adjusted models.Conclusion: The findings in the current study highlight the need to clarify the role of dietary protein intake in the maintenance of muscle mass and muscle strength in healthy older adults.