Dietary protein intake is not associated with 5-y change in mid-thigh muscle cross-sectional area by computed tomography in older adults: The Health, Aging, and Body Composition (Health ABC) Study

Background A higher protein intake is suggested to preserve muscle mass during aging and may therefore reduce the risk of sarcopenia. Objectives We explored whether the amount and type (animal or vegetable) of protein intake were associated with 5-y change in mid-thigh muscle cross-sectional area (CSA) in older adults (n = 1561). Methods Protein intake was assessed at year 2 by a Block food-frequency questionnaire in participants (aged 70-79 y) of the Health, Aging, and Body Composition (Health ABC) Study, a prospective cohort study. At year 1 and year 6 mid-thigh muscle CSA in square centimeters was measured by computed tomography. Multiple linear regression analysis was used to examine the association between energy-adjusted protein residuals in grams per day (total, animal, and vegetable protein) and muscle CSA at year 6, adjusted for muscle CSA at year 1 and potential confounders including prevalent health conditions, physical activity, and 5-y change in fat mass. Results Mean (95% CI) protein intake was 0.90 (0.88, 0.92) g · kg ^-1 · d ^-1 and mean (95% CI) 5-y change in muscle CSA was-9.8 (-10.6,-8.9) cm 2. No association was observed between energy-adjusted total (β =-0.00; 95% CI:-0.06, 0.06 cm 2; P = 0.982), animal (β =-0.00; 95% CI:-0.06, 0.05 cm 2; P = 0.923), or plant (β = +0.07; 95% CI:-0.06, 0.21 cm 2; P = 0.276) protein intake and muscle CSA at year 6, adjusted for baseline mid-thigh muscle CSA and potential confounders. Conclusions This study suggests that a higher total, animal, or vegetable protein intake is not associated with 5-y change in mid-thigh muscle CSA in older adults. This conclusion contradicts some, but not all, previous research. This trial was registered at www.trialregister.nl as NTR6930.