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Aging, sarcopenia, and protein intake 

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: Life Stage Nutrition and Metabolism
: protein, aging, sarcopenia, muscle
: Gregory Miller22 15 Oct 2012
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Sarcopenia, or the loss of muscle mass with aging, is a significant public health concern, with some estimating as much as a 1% loss of lean mass per year after the age of 30 years (1,2). Loss of muscle mass and associated declines in strength and mobility may not only adversely affect quality of life for elderly individuals, but also contribute greatly to health care costs. It has been estimated that sarcopenia results in an excess cost to the health care system of the United States of $18.4 billion a year due to associated disability (3,4). There is increasing evidence that one of the central tenants of sarcopenia is that the muscle of elderly individuals may suffer from a reduced responsiveness to anabolic stimuli, in particular to ingestion of dietary protein. Thus, older individuals may benefit from consumption of greater amounts of protein in order to aid in the prevention of sarcopenia; however, protein requirements for different age groups remain a source of considerable debate (5). As an example, recent research in this area has indicated that 25–30 g of high quality protein (i.e., protein that contains all of the essential amino acids) is required to maximally stimulate skeletal muscle protein synthesis (2); while this number may be as high as 40 grams in elderly individuals (6). Furthermore, in addition to the amount of protein consumed there may also be differences between protein sources, with higher quality protein sources (as determined by the quantity and bioavailability of essential amino acids) appearing to be more advantageous for promoting muscle protein synthesis (7,8). Based on these findings, there is general agreement among many experts in the field of protein nutrition that longer term clinical trials are needed to establish the optimal protein intake range for various population groups, older individuals in particular (2). In addition expanding on research examining different protein sources and accounting for bioavailability as well as concentrations of essential amino acids will help elucidate optimal protein sources (7,8,9). Longer term trials that consider endpoints beyond nitrogen balance will address much needed research on the role of dietary protein on quality of life indicators in older populations. Endpoints that have been recommended for sarcopenia research include measures of muscle strength (e.g., hand grip), muscle power (e.g., leg extension power), and gait speed to in order to assess indices of the individual's physical function, MRI and CT scans to determine muscle quality, and functional outcome measures that are translatable to performance daily life activities (3). References 1. Paddon-Jones D, Short KR, Campbell WW, Volpi E, Wolfe RR. Role of dietary protein in the sarcopenia of aging. Am J Clin Nutr. 2008 May;87(5):1562S-1566S. 2. Paddon-Jones D, Rasmussen BB. Dietary protein recommendations and the prevention of sarcopenia. Curr Opin Clin Nutr Metab Care. 2009 Jan;12(1):86-90. 3. Fielding RA, Vellas B, Evans WJ, Bhasin S, Morley JE, Newman AB, Abellan van Kan G, Andrieu S, Bauer J, Breuille D, Cederholm T, Chandler J, De Meynard C, Donini L, Harris T, Kannt A, Keime Guibert F, Onder G, Papanicolaou D, Rolland Y,Rooks D, Sieber C, Souhami E, Verlaan S, Zamboni M. Sarcopenia: an undiagnosed condition in older adults. Current consensus definition: prevalence, etiology,and consequences. International working group on sarcopenia. J Am Med Dir Assoc. 2011 May;12(4):249-56. 4. Janssen I, Shepard DS, Katzmarzyk PT, Roubenoff R. The healthcare costs of sarcopenia in the United States. J Am Geriatr Soc. 2004 Jan; 52(1):80–5. 5. Wolfe RR. The underappreciated role of muscle in health and disease. Am J Clin Nutr. 2006 Sep;84(3):475-82. 6. Yang Y, Breen L, Burd NA, Hector AJ, Churchward-Venne TA, Josse AR, Tarnopolsky MA, Phillips SM. Resistance exercise enhances myofibrillar protein synthesis with graded intakes of whey protein in older men. Br J Nutr. 2012 Feb 7:1-9. 7. Phillips SM, Tang JE, Moore DR. The role of milk- and soy-based protein in support of muscle protein synthesis and muscle protein accretion in young and elderly persons. J Am Coll Nutr. 2009 Aug;28(4):343-54. 8. Tang JE, Phillips SM. Maximizing muscle protein anabolism: the role of protein quality. Curr Opin Clin Nutr Metab Care. 2009 Jan;12(1):66-71. 9. Wilkinson SB, Tarnopolsky MA, Macdonald MJ, Macdonald JR, Armstrong D, Phillips SM. Consumption of fluid skim milk promotes greater muscle protein accretion after resistance exercise than does consumption of an isonitrogenous and isoenergetic soy-protein beverage. Am J Clin Nutr. 2007 Apr;85(4):1031-40.

1) Shalene McNeill15 (15 Oct 2012)
Agree with this post on sarcopenia, particularly given the size of the aging population and the impact of gradual loss of muscle associated with aging on health. Both amount (i.e. intakes within the full spectrum of the AMDR range)as well as source (plant and animal, striated and non-striated)should be considered.