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 (beta = -0.00; 95% CI: -0.06, 0.06 cm(2); P = 0.982), animal (beta =-0.00; 95% CI: -0.06, 0.05 cm(2); P = 0.923), or plant (beta = + 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 midthigh muscle CSA in older adults. This conclusion contradicts some, but not all, previous research. This trial was registered at www.trialregister.nl as NTR6930.