Breakfast Protein Quality and Muscle Strength in Japanese Older Adults: A Community-Based Longitudinal Study.

Objectives: The amount of breakfast protein intake is important for maintaining muscle strength. However, the effect of breakfast protein quality (ie, bioavailability) remains unclear. We investigated the association between breakfast protein quality and the incidence of muscle weakness.
Design: Longitudinal study.
Setting and Participants: Healthy older adults age 60-83 years without stroke, arthritis, Parkinson disease, or muscle weakness at baseline (maximum follow-up period and participations were 9.2 years and 5 times, respectively).
Methods: Weakness was defined by the Asian Working Group for Sarcopenia 2019 criteria, using grip strength. Breakfast protein quality was evaluated using the protein digestibility-corrected amino acid score (PDCAAS), where higher scores represent higher quality, calculated from 3-day dietary records. Participants were classified according to sex-stratified tertiles of breakfast PDCAAS (ie, low to high groups). The association between PDCAAS and incident weakness was analyzed using the generalized estimating equation, after adjusting for sex, age, follow-up time, grip strength, body mass index, physical activity, cognition, education, smoking, economics, medical history, lunch and dinner PDCAASs, and energy and protein intake during 3 regular meals at baseline.
Results: Overall, 14.4% of the initial sample was excluded owing to a diagnosis of weakness-related diseases, and 58.3% (n = 701) had at least 1 follow-up measurement for inclusion in the analysis. The mean ± SD follow-up period was 6.9 ± 2.1 years; the cumulative number of participants was 3019, and 282 developed weakness. Using the low PDCAAS group as the reference, the adjusted odds ratios (95% CIs) for incident weakness in the middle and high PDCAAS groups were 0.71 (0.43-1.18) and 0.50 (0.29-0.86), respectively.
Conclusions and Implications: Higher breakfast protein quality was associated with a reduction in incident weakness in older adults, independent of protein intake. These findings may highlight the role of protein quality for muscle health in older adults.
(Copyright © 2021 The Authors. Published by Elsevier Inc. All rights reserved.)