(05-07-11) Whole-body and muscle protein metabolism are not affected by acute deviations from habitual protein intake in older men: the Hormona

Whole-body and muscle protein metabolism are not affected by acute deviations from habitual protein intake in older men: the Hormonal Regulators of Muscle and Metabolism in Aging (HORMA) Study1,2,3,4

1. Kevin E Yarasheski,
2. Carmen Castaneda-Sceppa,
3. Jiaxiu He,
4. Miwa Kawakubo,
5. Shalender Bhasin,
6. Ellen F Binder,
7. E Todd Schroeder,
8. Ronenn Roubenoff,
9. Stan P Azen, and
10. Fred R Sattler
+ Author Affiliations
1. 1From the Department of Medicine, Washington University, St Louis, MO (KEY and EFB); the Jean Mayer US Department of Agriculture, Human Nutrition Research Center on Aging at Tufts University, Boston, MA (CC-S and RR); the Department of Medicine, Division of Biokinesiology, Department of Preventive Medicine, University of Southern California, Los Angeles, CA (JH, MK, ETS, SPA, and FRS); and the Department of Medicine and the Boston Claude D Pepper Older Americans Independence Center, Boston University School of Medicine, Boston, MA (SB).
+ Author Notes
? ↵2 The opinions, findings, conclusions, or recommendations expressed in this publication are those of the authors and do not necessarily reflect the views of the USDA.
? ↵3 Supported in part by NIH R01 AG18169 and NCRR GCRC (M01 RR000043) at the University of Southern California, NCRR GCRC (M01 RR000036) and the Biomedical Mass Spectrometry Facility (RR000954, DK020579 and DK056341) at Washington University School of Medicine, the USDA ARS Cooperative Agreement (58-1950-9-001) and GCRC (M01RR000054) at Tufts University, and NIH U01 AG14369 and R01 DK70534 at Boston Medical Center, Boston University School of Medicine.
? ↵4 Address reprint requests and correspondence to KE Yarasheski, Washington University School of Medicine, 660 South Euclid Avenue, Campus Box 8127, St Louis, MO. E-mail: [email protected].
Abstract
Background: Acute deviations in protein intake before the quantification of protein kinetics in older humans may explain the controversy over the effects of older age on muscle protein synthesis and proteolysis rates.
Objective: We hypothesized that an acute decrease in protein intake from the habitual intake is associated with lower muscle protein synthesis and higher proteolysis rates, whereas an acute increase in protein intake from the habitual intake is associated with higher muscle protein synthesis and lower proteolysis rates.
Design: In 112 community-dwelling healthy men aged 65?90 y, we quantified resting whole-body [1,2-13C2]leucine kinetics, muscle mixed protein fractional synthesis rates (FSRs), and muscle proteasome proteolytic enzyme activities after participants consumed for 3 d controlled research meals (0.9?1.1 g protein ? kg−1 ? d−1) that contained more or less protein than that habitually consumed and that induced alterations in nitrogen balance.
Results: Protein kinetic parameters were not significantly different between the groups, despite controlled research protein intakes that were lower (−0.2 to −0.3 g ? kg−1 ? d−1) or higher (+0.2 g ? kg−1 ? d−1) than habitual intakes and that induced negative (−22 to −25 mg ? kg−1 ? d−1) or positive (22?25 mg ? kg−1 ? d−1) nitrogen balance. Within these acutely altered protein intake and nitrogen balance boundaries, a reduction in protein intake from habitual intake and induction of negative nitrogen balance were not associated with higher proteolysis or lower muscle FSR, and an acute increase in protein intake from habitual intake and induction of positive nitrogen balance were not associated with lower proteolysis or higher muscle FSR. A higher quantitative insulin sensitivity check index was associated with lower whole-body proteolysis rates.
Conclusions: The practice of acutely controlling protein intake, even at intakes lower than habitual intakes that induce negative nitrogen balance, before quantifying human protein kinetics does not significantly reduce muscle protein synthesis or increase proteolysis. Factors other than protein intake explain lower muscle protein synthesis rates with advanced age. This trial is registered at clinicaltrials.gov as NCT00183040.

Source: Am J Clin Nutr July 2011 vol. 94 no. 1 172-181

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