Kerstetter JE et al. - 46454 N - J Clin Endocrinol Metab 2015 ; : jc20143792.
CONTEXT: It has been assumed that the increase in urine calcium (UCa) that accompanies an increase in dietary protein was due to increased bone resorption. However, studies using stable Ca isotopes have found that dietary protein increases Ca absorption without increasing bone resorption.
OBJECTIVE: To investigate the impact of a moderately-high protein diet on bone mineral density (BMD).
DESIGN: A randomized, double-blind, placebo-controlled trial of protein supplementation daily for 18 months.
SETTING: Two institutional research centers.
PARTICIPANTS: Two hundred and eight older women and men with a BMI between 19 and 32 kg/m2 and a self-reported protein intake between 0.6 and 1.0 g/kg.
INTERVENTION: Subjects were asked to incorporate either a 45 g whey protein or isocaloric maltodextrin supplement into their usual diet for 18 months. MAIN OUTCOME MEASURE: BMD by dual-energy x-ray absorptiometry (DXA), body composition, and markers of skeletal and mineral metabolism were measured at baseline, 9 and 18 months.
RESULTS: There were no significant differences between groups for changes in L-spine BMD (primary outcome) or the other skeletal sites of interest. Truncal lean mass was significantly higher in the protein group at 18 months (p = 0.048). CTX (p = 0.0414), insulin-like growth factor-1 (IGF-1, p = 0.0054) and urinary urea (p <0.001) were also higher in the protein group at the end of the study period. There was no difference in eGFR at 18 months.
CONCLUSION: Our data suggest that protein supplementation above the RDA (0.8 g/kg) may preserve fat-free mass without adversely affecting skeletal or renal function in healthy older adults.