HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Cited by other online articles Google Scholar Articles by Campbell, W. W. Articles by Evans, W. J. Articles citing this Article PubMed PubMed Citation Articles by Campbell, W. W. Articles by Evans, W. J.

The Recommended Dietary Allowance for Protein May Not Be Adequate for Older People to Maintain Skeletal Muscle

^a The Donald W. Reynolds Department of Geriatrics, University of Arkansas for Medical Sciences, Little Rock.
^b The Geriatric Research, Education, and Clinical Center, Central Arkansas Veterans Healthcare System, Little Rock.
^c Metabolism Unit, Shriners Burns Institute and the University of Texas Medical Branch, Galveston.

William J. Evans, Nutrition, Metabolism and Exercise Division, Renolds Department of Geriatrics and GRECC, 4301 West Markham Street, Slot 806, Little Rock, AR 72205 E-mail: evanswilliamj{at}exchange.uams.edu.

Decision Editor: John E. Morley, MB, BCh

Background. Inadequate dietary protein intake results in loss of skeletal muscle mass. Some shorter-term nitrogen balance studies suggest that the Recommended Dietary Allowance (RDA) of protein may not be adequate for older people. The aim of this study was to assess the adequacy of the RDA of protein for older people by examining longer-term responses in urinary nitrogen excretion, whole-body protein metabolism, whole-body composition, and mid-thigh muscle area.

Methods. This was a 14-week precisely controlled diet study. Ten healthy, ambulatory men and women, aged 55 to 77 years, were provided eucaloric diets that contained 0.8 g protein·kg^-1·day^-1. The study was conducted at a General Clinical Research Center using an outpatient setting for 11 weeks and an inpatient setting for 3 weeks. The main outcome measures included urinary nitrogen excretion, postabsorptive and postprandial whole-body leucine kinetics via infusion of L-[1-¹³C]-leucine, whole-body density via hydrostatic weighing, total body water via deuterium oxide dilution, and mid-thigh muscle area via computed tomography scans.

Results. Mean urinary nitrogen excretion decreased over time from Weeks 2 to 8 to 14 (p = .025). At Week 14, compared with Week 2, there were no changes in postabsorptive or postprandial leucine kinetics (turnover, oxidation, incorporation into protein via synthesis, release via breakdown, or balance). Whole-body composition (% body fat, fat-free mass, and protein + mineral mass) did not change over time in these weight-stable subjects. Mid-thigh muscle area was decreased by -1.7 ± 0.6 cm² (p = .019) at Week 14 compared with Week 2. The loss of mid-thigh muscle area was associated with the decrease in urinary nitrogen excretion (Spearman r = .83, p = .010).

Conclusions. The maintenance of whole-body leucine metabolism and whole-body composition is generally consistent with a successful adaptation to the RDA for protein. However, the decrease in mid-thigh muscle area and the association with decreased urinary nitrogen excretion are consistent with a metabolic accommodation. These results suggest that the RDA for protein may not be adequate to completely meet the metabolic and physiological needs of virtually all older people.

This article has been cited by other articles: (Search Google Scholar for Other Citing Articles)

				R. R Wolfe The underappreciated role of muscle in health and disease Am. J. Clinical Nutrition, September 1, 2006; 84(3): 475 - 482. [Abstract] [Full Text] [PDF]

				S. Fujita and E. Volpi Amino Acids and Muscle Loss with Aging J. Nutr., January 1, 2006; 136(1): 277S - 280S. [Abstract] [Full Text] [PDF]

				A. B Newman, J. S. Lee, M. Visser, B. H Goodpaster, S. B Kritchevsky, F. A Tylavsky, M. Nevitt, and T. B Harris Weight change and the conservation of lean mass in old age: the Health, Aging and Body Composition Study Am. J. Clinical Nutrition, October 1, 2005; 82(4): 872 - 878. [Abstract] [Full Text] [PDF]

				L. Holm, B. Esmarck, C. Suetta, K. Matsumoto, T. Doi, M. Mizuno, B. F. Miller, and M. Kjaer Postexercise Nutrient Intake Enhances Leg Protein Balance in Early Postmenopausal Women J. Gerontol. A Biol. Sci. Med. Sci., September 1, 2005; 60(9): 1212 - 1218. [Abstract] [Full Text] [PDF]

				M. Visser, S. B Kritchevsky, A. B Newman, B. H Goodpaster, F. A Tylavsky, M. C Nevitt, T. B Harris, and for the Health, Aging and Body Composition Study Lower serum albumin concentration and change in muscle mass: the Health, Aging and Body Composition Study Am. J. Clinical Nutrition, September 1, 2005; 82(3): 531 - 537. [Abstract] [Full Text] [PDF]

				H. C. Dreyer and E. Volpi Role of Protein and Amino Acids in the Pathophysiology and Treatment of Sarcopenia J. Am. Coll. Nutr., April 1, 2005; 24(2): 140S - 145S. [Abstract] [Full Text] [PDF]

				W. J. Evans Protein Nutrition, Exercise and Aging J. Am. Coll. Nutr., December 1, 2004; 23(suppl_6): 601S - 609S. [Abstract] [Full Text] [PDF]

				J. Bohe, A. Low, R. R. Wolfe, and M. J. Rennie Human muscle protein synthesis is modulated by extracellular, not intramuscular amino acid availability: a dose-response study J. Physiol., October 1, 2003; 552(1): 315 - 324. [Abstract] [Full Text] [PDF]

				T. J. Doherty Invited Review: Aging and sarcopenia J Appl Physiol, October 1, 2003; 95(4): 1717 - 1727. [Abstract] [Full Text] [PDF]

				S. Chevalier, R. Gougeon, K. Nayar, and J. A Morais Frailty amplifies the effects of aging on protein metabolism: role of protein intake Am. J. Clinical Nutrition, September 1, 2003; 78(3): 422 - 429. [Abstract] [Full Text] [PDF]

				E. Volpi, H. Kobayashi, M. Sheffield-Moore, B. Mittendorfer, and R. R Wolfe Essential amino acids are primarily responsible for the amino acid stimulation of muscle protein anabolism in healthy elderly adults Am. J. Clinical Nutrition, August 1, 2003; 78(2): 250 - 258. [Abstract] [Full Text] [PDF]

				L. J. Kruskall, W. W. Campbell, and W. J. Evans The Atwater Energy Equivalents Overestimate Metabolizable Energy Intake in Older Humans: Results from a 96-Day Strictly Controlled Feeding Study J. Nutr., August 1, 2003; 133(8): 2581 - 2584. [Abstract] [Full Text] [PDF]

				A. M. Kenny, L. Dawson, A. Kleppinger, M. Iannuzzi-Sucich, and J. O. Judge Prevalence of Sarcopenia and Predictors of Skeletal Muscle Mass in Nonobese Women Who Are Long-Term Users of Estrogen-Replacement Therapy J. Gerontol. A Biol. Sci. Med. Sci., May 1, 2003; 58(5): M436 - 440. [Abstract] [Full Text] [PDF]

				M. Iannuzzi-Sucich, K. M. Prestwood, and A. M. Kenny Prevalence of Sarcopenia and Predictors of Skeletal Muscle Mass in Healthy, Older Men and Women J. Gerontol. A Biol. Sci. Med. Sci., December 1, 2002; 57(12): M772 - 777. [Abstract] [Full Text] [PDF]

				H. Fouillet, C. Bos, C. Gaudichon, and D. Tome Approaches to Quantifying Protein Metabolism in Response to Nutrient Ingestion J. Nutr., October 1, 2002; 132(10): 3208S - 3218. [Abstract] [Full Text] [PDF]

				M. D Haub, A. M Wells, M. A Tarnopolsky, and W. W Campbell Effect of protein source on resistive-training-induced changes in body composition and muscle size in older men Am. J. Clinical Nutrition, September 1, 2002; 76(3): 511 - 517. [Abstract] [Full Text] [PDF]