Objectives: Defining an adequate protein intake in older adults remains unresolved. We examined the association between calibrated protein intake and comprehensive frailty by sex in the Kyoto-Kameoka study. Design: Cross-sectional study of baseline data. Setting and Participants: The study included 5679 Japanese participants aged 65 years or older. Methods: Calibration coefficients were estimated from food frequency questionnaires and 7-day dietary records as a reference. Comprehensive frailty was evaluated using the 25-item Kihon Checklist (KCL) and defined as a total KCL score of ≥7points. Sex-specific calibrated protein intakes were presented as % of energy, per kg of actual body weight (BW), and per kg of ideal BW. Results: Multiple logistic regression analysis shoed that calibrated protein intake is inversely associated with comprehensive frailty. The association between protein intake and comprehensive frailty was also evaluated using curve fitting with non-linear regression, a weak U-shaped association was found in males and an L-shaped association in females. Men had a low prevalence of frailty at a calibrated protein intake of 15–17% energy from protein, 1.2 g/kg actual BW/day, or 1.4 g/kg ideal BW/day, and women had a low prevalence of frailty at 17–21% energy from protein or 1.6 g/kg ideal BW/day, with the prevalence of frailty remaining unchanged at higher protein intakes. Meanwhile, the inverse relationship between protein intake per ABW and frailty showed a gradual decrease at 1.4 g/kg ABW/day for protein in women. Conclusions and Implications: A non-linear relationship was found between calibrated protein intake and frailty, with a U-shaped association in men and an L-shaped association in women. Adequate protein intake in healthy Japanese older adults was higher than the current recommended daily allowance.
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