ORIGINAL ARTICLE Protein intake and lean body mass preservation during energy intake restriction in overweight older adults EMP Backx 1,2 , M Tieland 1,2 , KJ Borgonjen-van den Berg 1 , PR Claessen 1 , LJC van Loon 2,3 and LCPGM de Groot 1,2 BACKGROUND: Dietary-induced weight loss is generally accompanied by a decline in skeletal muscle mass. The loss of muscle mass leads to a decline in muscle strength and impairs physical performance. A high dietary protein intake has been suggested to allow muscle mass preservation during energy intake restriction. OBJECTIVE: To investigate the impact of increasing dietary protein intake on lean body mass, strength and physical performance during 12 weeks of energy intake restriction in overweight older adults. DESIGN: Sixty-one overweight and obese men and women (63 ± 5 years) were randomly assigned to either a high protein diet (HP; 1.7 g kg - 1 per day; n= 31) or normal protein diet (NP; 0.9 g kg - 1 per day; n= 30) during a 12-week 25% energy intake restriction. During this controlled dietary intervention, 90% of the diet was provided by the university. At baseline and after the intervention, body weight, lean body mass (dual-energy X-ray absorptiometry), leg strength (1-repetition maximum), physical performance (Short Physical Performance Battery, 400 m) and habitual physical activity (actigraph) were assessed. RESULTS: Body weight declined in both groups with no differences between the HP and NP groups (-8.9 ± 2.9 versus -9.1 ± 3.4 kg, respectively; P = 0.584). Lean body mass declined by 1.8 ± 2.2 and 2.1 ± 1.4 kg, respectively, with no significant differences between groups (P = 0.213). Leg strength had decreased during the intervention by 8.8 ± 14.0 and 8.9 ± 12.8 kg, with no differences between groups (P = 0.689). Physical performance as measured by 400 m walking speed improved in both groups, with no differences between groups (P = 0.219). CONCLUSIONS: Increasing protein intake above habitual intake levels (0.9 g kg - 1 per day) does not preserve lean body mass, strength or physical performance during prolonged energy intake restriction in overweight older adults. International Journal of Obesity advance online publication, 3 November 2015; doi:10.1038/ijo.2015.182 INTRODUCTION Muscle mass and strength are main predictors of physical function and health status in older adults. During a period of energy intake restriction, the decline in body weight is accompanied by a significant loss of muscle mass and strength. 1,2 This decline in muscle mass and strength may even offset the metabolic benefits of the reduction of excess body fat. Novel strategies to preserve muscle mass during energy intake restriction are warranted. It has been well established that nutrition is an important factor in regulating muscle mass maintenance. 3,4 Dietary protein intake stimulates muscle protein synthesis and allows postprandial muscle protein accretion. 5 It has been suggested that increasing the protein content of the diet might be an effective interven- tional strategy to preserve muscle mass during prolonged energy intake restriction, thereby maintaining strength and physical performance. Whereas several intervention studies show that increasing protein intake during a period of energy intake restriction can alleviate the loss of lean body mass (LBM) or increase the loss of fat mass (FM), 6–8 other studies have failed to confirm these findings. 9,10 The discrepancy in the literature may be attributed to differences in the selected study population, the applied nutritional intervention and/or compliance and adherence of the subjects to the diet. Most of the previous work investigating the impact of different protein intakes on LBM preservation during energy intake restriction have been conducted in young to middle-aged adults. 7,8,11–16 However, the results of these studies may not be translated to the older population because of differences in muscle mass and the prevalence of anabolic resistance. 17–19 Another explanation for the discrepancy in the literature is the protein content of the applied intervention diets. Previous studies have compared the impact of a wide variety of protein intakes on LBM preservation during prolonged energy intake restriction, ranging from 0.6 to 0.8 versus 1.1 to 2.4 g protein kg - 1 body weight per day. 8,9,20,21 Furthermore, the compliance and adherence to a dietary intervention requires careful attention, with nutrition being provided and consumed under strict supervision. 22,23 In the present study, we investigate the impact of an increase in dietary protein intake on the preservation of muscle mass during prolonged energy intake restriction in overweight, older adults. Maintenance of habitual protein intake (0.9–1.0 g kg - 1 per day) has previously been shown to be required for muscle mass preservation. 24,25 Therefore, we assess the impact of energy intake restriction on LBM preservation with protein intakes being set at 1.7 versus 0.9 g kg - 1 per day. We hypothesize that a high protein (HP) intake can preserve LBM during energy intake restriction in overweight, older adults. To ensure proper compliance and adherence to the intervention diet, a strictly controlled dietary intervention is performed. 1 Division of Human Nutrition, Wageningen University, Wageningen, The Netherlands; 2 Top Institute Food and Nutrition, Wageningen, The Netherlands and 3 NUTRIM School of Nutrition and Translational Research in Metabolism, Maastricht University Medical Centre, Maastricht, The Netherlands. Correspondence: Professor LCPGM de Groot, Division of Human Nutrition, Wageningen University, PO Box 8129, Wageningen 6700EV, The Netherlands. E-mail: Lisette.deGroot@wur.nl Received 25 March 2015; revised 13 August 2015; accepted 23 August 2015; accepted article preview online 16 October 2015 International Journal of Obesity (2015), 1 – 6 © 2015 Macmillan Publishers Limited All rights reserved 0307-0565/15 www.nature.com/ijo