Applied nutritional investigation Glomerular filtration rate after a 12-wk resistance exercise program with post-exercise protein ingestion in community dwelling elderly Alfons Ramel Ph.D. a, * , Atli Arnarson M.Sc. a , Olof G. Geirsdottir Ph.D. a, b , Palmi V. Jonsson M.D. b, c , Inga Thorsdottir Ph.D. a a Unit for Nutrition Research, National University Hospital and Faculty of Food Science and Nutrition, University of Iceland, Reykjavik, Iceland b The Icelandic Gerontological Research Center, National University Hospital and Faculty of Medicine, University of Iceland, Reykjavik, Iceland c Department of Geriatrics, National University Hospital and Faculty of Medicine, University of Iceland, Reykjavik, Iceland article info Article history: Received 20 August 2012 Accepted 11 October 2012 Keywords: Glomerular filtration rate Cockcroft-Gault formula Whey protein Strength Old adults abstract Objective: Increased protein intake and resistance exercise can be beneficial for maintenance of lean body mass (LBM) in older adults. However, these factors could also negatively affect renal function. We investigated changes in renal function after a 12-wk resistance exercise program combined with protein supplementation in community dwelling older adults. Methods: Patients (N ¼ 237, 73.7  5.7 y, 58.2% female) participated in a 12-wk resistance exercise program (3 times/wk) designed to increase strength and muscle mass of major muscle groups. Participants were randomly assigned to one of three dietary supplements consumed directly after training: whey protein drink (20 g whey protein, 20 g carbohydrates), milk protein drink (20 g milk protein, 20 g carbohydrates), or carbohydrate drink (40 g carbohydrates). Renal function was estimated as glomerular filtration rate (GFR, Cockcroft-Gault formula), and dietary intake was measured as 3-d-weighed food record at baseline and endpoint. Results: During the intervention, energy intake did not increase. Carbohydrate intake increased in the carbohydrate group and protein intake increased in the milk group, both approximately in accordance with the supplementation. In the whey group, protein intake did not increase, but carbohydrate intake did. GFR increased after the intervention (þ4.4 mL/min/1.73 m 2 ; P < 0.001), and the changes were similar in men and women or in the age quartiles. Changes in GFR at endpoint were not associated with LBM, dietary supplements, or total protein intake. Conclusions: A 12-wk resistance exercise program combined with protein supplementation in community dwelling older adults does not negatively affect GFR. The supplementation had only minor effects on total dietary intake. Ó 2013 Elsevier Inc. All rights reserved. Introduction Aging is associated with changes in body composition, i.e., decreased lean body mass (LBM), increased fat mass, and a more central distribution of adipose tissue [1]. The loss of LBM accel- erates after the age of 60 and is a contributor to disability, frailty, and functional impairments [2,3]. Higher LBM has also been reported to be a predictor of lower mortality in older adults [4]. There is a large variation between individuals in the changes of LBM during aging partly explained by physical activity, in particular resistance exercise [5,6]. Inadequate dietary intake, especially protein intake, has been associated with decreased LBM [7]. Dietary protein affects muscle mass by the stimulation of muscle protein synthesis after the absorption of amino acids into muscle cells. It has been questioned whether optimal intake for older adults should be higher, e.g., 1.2 g/kg to 1.5 g/kg body weight, [7,8] than the current RDA of 0.8 g/kg body weight [9]. Concerns have been raised about potential detrimental effects of increased protein intake on renal function, as reflected by reduced glomerular filtration [7]. Usually, the glomerular filtration rate (GFR), a parameter of renal function, declines by 1 mL/min per 1.73 m 2 after the age of 50 y [10]. And there is a general agreement that protein intake should be limited in individuals with renal disease because it can contribute to the deterioration of kidney function [11]. However, according to a recent review on protein * Corresponding author. Tel.: þ354 543 8417; fax: þ354 543 4824. E-mail address: alfonsra@hi.is (A. Ramel). 0899-9007/$ - see front matter Ó 2013 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.nut.2012.10.002 Contents lists available at ScienceDirect Nutrition journal homepage: www.nutritionjrnl.com Nutrition 29 (2013) 719–723