健康な高齢者におけるホエイプロテインとアルカリ補給が筋肉の健康に及ぼす独立した影響：要因計画無作為化比較試験

BACKGROUND: Aging is accompanied by reduced muscle protein synthesis and increased circulating acid, both of which contribute to declines in muscle health. OBJECTIVES: To determine the effects of whey protein (WP) and alkali (potassium bicarbonate, KHCO) supplementation on muscle performance and mass in healthy older adults. METHODS: In this randomized, 2 × 2 factorial, placebo-controlled study, healthy adults aged ≥65 years were assigned to either WP (1.5 g/kg/d) plus KHCO (81 mmol/d), WP plus placebo-KHCO, placebo-WP plus KHCO, or double placebo. Double leg press muscle power (primary outcome), physical performance, lean mass by dual energy x-ray absorptiometry, muscle mass by D-creatine dilution, and serum insulin-like growth factor 1 (IGF-1) were measured at baseline and 24 weeks. Primary analyses estimated main effects of WP compared with placebo-WP and KHCO compared with placebo-KHCO using factorial comparisons "at-the-margins," following CONSORT/SPIRIT recommendations for factorial trials. Between-group differences in the 24-wk outcomes were estimated using analysis of covariance adjusted for baseline value, age, and sex. RESULTS: In the intention-to-treat sample (n = 128), 47.7% were female, mean ± SD age was 74 ± 6 y, and baseline protein intake was 0.85 ± 0.30 g/kg/d. Neither WP nor KHCO affected muscle power compared with their respective placebo {WP to placebo-WP difference 4.7 watts [95% confidence interval (CI): -21.1,30.5; P = 0.72]; KHCO to placebo-KHCO difference -13.6 watts [95% CI: -39.6, 12.4; P = 0.30]}. No group differences were noted in physical performance or muscle mass. However, 24-wk mean IGF-1 level was higher in the WP and KHCO groups compared with their respective placebo [WP to placebo-WP difference 14.2 ng/mL (95% CI: 7.5, 21.0; P < 0.01); KHCO to placebo-KHCO difference 7.2 ng/mL (95% CI: 0.4, 13.9; P = 0.04)]. CONCLUSIONS: In healthy free-living older adults reporting a protein intake at the current recommended daily allowance, neither increasing protein to 1.5 g/kg/d with WP nor adding a KHCO supplement for 24 wk improved measures of muscle power, physical performance, or muscle mass despite achieving higher circulating IGF-1 levels. CLINICAL TRIAL REGISTRY NUMBER: This trial was registered as NCT04048616 at https://clinicaltrials.gov/study/NCT04048616?term=ceglia&rank=1.