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Dirk Aerenhouts, Jelle Van Cauwenberg, Jacques Remi Poortmans, Ronald Hauspie, and Peter Clarys

This study aimed to estimate nitrogen balance and protein requirements in adolescent sprint athletes as a function of growth rate and physical development. Sixty adolescent sprint athletes were followed up biannually over a 2-yr period. Individual growth curves and age at peak height velocity were determined. Skeletal muscle mass (SMM) was estimated based on anthropometric measurements and fat mass was estimated by underwater densitometry. Seven-day diet and physical activity diaries were completed to estimate energy balance and protein intake. Nitrogen analysis of 24-hr urine samples collected on 1 weekday and 1 weekend day allowed calculation of nitrogen balance. Body height, weight, and SMM increased throughout the study period in both genders. Mean protein intakes were between 1.4 and 1.6 g kg−1 day−1 in both genders. A protein intake of 1.46 g kg−1 day−1 in girls and 1.35 g kg−1 day−1 in boys was needed to yield a positive nitrogen balance. This did not differ between participants during and after their growth spurt. None of the growth parameters was significantly related to nitrogen balance. It can be concluded that a mean protein intake around 1.5 g kg−1 day−1 was sufficient to stay in a positive nitrogen balance, even during periods of peak growth. Therefore, protein intake should not be enhanced in peak periods of linear or muscular growth.

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Brian D. Roy, Katherine Luttmer, Michael J. Bosman, and Mark A. Tarnopolsky

The purpose of this investigation was to determine the influence of post-exercise macronutrient intake on weight loss, protein metabolism, and endurance exercise performance during a period of increased training volume. Ten healthy young female endurance athletes performed 4 60-min bouts of cycle ergometry at ~65% of V̇O2peak on 4 days (day 1, 3, 4, and 6) during 2 separate 1-week periods. On day 7. participants performed a ride to exhaustion at ~75% of V̇O2peak. One of the 7-day periods served as a control condition, where a placebo beverage was consumed following the exercise bouts on days 1, 3, 4, and 6 (CON). During the other 7-day protocol (POST), participants consumed a predefined formula beverage with added carbohydrate following the exercise bouts on days 1. 3,4, and 6. Energy intake and macronutrient proportions were the same between the 2 trials; the only difference was the timing at which the macronutrients were consumed. Calculated fat oxidation was greater during exercise on day 6 during POST as compared to CON (p < .05). Glucose and insulin concentrations were significantly higher (p < .05) following exercise during POST as compared to CON. There was a trend (p = .06) for nitrogen balance to be greater on days 5 and 6 with POST as compared to CON. Time to exhaustion during exercise on day 7 was longer during POST as compared to CON (p < .05). POST resulted in a maintenance of body weight during the 7-day protocol, while there was a significant (p < .05) reduction with CON. It was concluded that post-exercise macronutrient intake following endurance exercise can attenuate reductions in body weight and improve nitrogen balance during 7 days of increased energy expenditure. Importantly, post-exercise supplementation improved time to exhaustion during a subsequent bout of endurance exercise.

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Jacques R. Poortmans and Olivier Dellalieux

Excess protein and amino acid intake have been recognized as hazardous potential implications for kidney function, leading to progressive impairment of this organ. It has been suggested in the literature, without clear evidence, that high protein intake by athletes has no harmful consequences on renal function. This study investigated body-builders (BB) and other well-trained athletes (OA) with high and medium protein intake, respectively, in order to shed light on this issue. The athletes underwent a 7-day nutrition record analysis as well as blood sample and urine collection to determine the potential renal consequences of a high protein intake. The data revealed that despite higher plasma concentration of uric acid and calcium. Group BB had renal clearances of creatinine, urea, and albumin that were within the normal range. The nitrogen balance for both groups became positive when daily protein intake exceeded 1.26 g · kg−1 but there were no correlations between protein intake and creatinine clearance, albumin excretion rate, and calcium excretion rate. To conclude, it appears that protein intake under 2.8 g·kg−1 does not impair renal function in well-trained athletes as indicated by the measures of renal function used in this study.

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Peter W.R. Lemon

This paper reviews the factors (exercise intensity, carbohydrate availability, exercise type, energy balance, gender, exercise training, age, and timing of nutrient intake or subsequent exercise sessions) thought to influence protein need. Although there remains some debate, recent evidence suggests that dietary protein need increases with rigorous physical exercise. Those involved in strength training might need to consume as much as 1.6 to 1.7 g protein ⋅ kg−1 day−1 (approximately twice the current RDA) while those undergoing endurance training might need about 1.2 to 1.4 g ⋅ kg−1 day−1 (approximately 1.5 times the current RDA). Future longitudinal studies are needed to confirm these recommendations and assess whether these protein intakes can enhance exercise performance. Despite the frequently expressed concern about adverse effects of high protein intake, there is no evidence that protein intakes in the range suggested will have adverse effects in healthy individuals.

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Michael J. Ormsbee, Jeffrey A. Clapper, Joan L. Clapper, and Matthew D. Vukovich

This study was designed to investigate the impact of dietary protein intake on serum concentrations of IGF-I and IGFBP-1 and relative amounts of serum IGFBP-3 during 6 d of physical activity. Ten men (23.8 ± 2.0 y of age) were assigned to 1 of 3 trials in a random crossover design. Each trial was isocaloric but with varying amounts of dietary protein: 50 g, 100 g, or 200 g. Subjects expended 500 kcal through treadmill running or weightlifting on alternate days for 6 d. Fasting blood samples were obtained for measurement of IGF-I, IGFBP-1, and IGFBP-3. Pre–post 24-h urine was measured for urea nitrogen. 50 g/d of protein resulted in a negative nitrogen balance, whereas 100 g/d and 200 g/d resulted in a positive nitrogen balance—200 g greater (P < 0.05) than 50 g and 100 g. Baseline IGF-I, BP-1, and BP-3 were not different among treatments. IGF-I decreased (P = 0.002) during the 6 d. Post intervention IGFBP-I was greater (P = 0.03) than at baseline. Post intervention IGFBP-3 values were not different from baseline or between trials. A 6-d modification of protein intake, while in energy balance, during a strength and conditioning program does not appear to modify serum concentrations of IGF-I or IGFBP-1 or relative amounts of IGFBP-3.

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Protein Needs of Physically Active Children

Re: Golden Horseshoe Pediatric Exercise Group: Proceedings Paper

Kimberly A. Volterman and Stephanie A. Atkinson

Current Dietary Reference Intakes (DRI) for protein for children and youth require revision as they were derived primarily on nitrogen balance data in young children or extrapolated from adult values; did not account for the possible influence of above average physical activity; and did not set an upper tolerable level of intake. Revision of the protein DRIs requires new research that investigates: 1) long-term dose-response to identify protein and essential amino acid requirements of both sexes at various pubertal stages and under differing conditions of physical activity; 2) the acute protein needs (quantity and timing) following a single bout of exercise; 3) the potential adverse effects of chronic high intakes of protein; and 4) new measurement techniques (i.e., IAAO or stable isotope methodologies) to improve accuracy of protein needs. While active individuals may require protein in excess of current DRIs, most active Canadian children and youth have habitual protein intakes that exceed current recommendations.

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Peter W. R. Lemon

The current recommended daily allowance (RDA) for protein is based primarily on data derived from subjects whose lifestyles were essentially sedentary. More recent well-designed studies that have employed either the classic nitrogen balance approach or the more technically difficult metabolic tracer technique indicate that overall protein needs (as well as needs for some specific individual amino acids) are probably increased for those who exercise regularly. Although the roles of the additionally required dietary protein and amino acids are likely to be quite different for those who engage in endurance exercise (protein required as an auxiliary fuel source) as opposed to strength exercise (amino acids required as building blocks for muscle development), it appears that both groups likely will benefit from diets containing more protein than the current RDA of 0.8 g · kg−1 · day 1 . Strength athletes probably need about 1.4-1.8 g · kg−1 · day 1 and endurance athletes about 1.2-1.4 g · kg−1 · day 1 .

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Michael J. Ormsbee, Brandon D. Willingham, Tasha Marchant, Teresa L. Binkley, Bonny L. Specker, and Matthew D. Vukovich

of ∼16–25% above the recommended 0.8 g·kg −1 ·day −1 ( Lemon et al., 1997 ). Based on nitrogen balance data, a protein requirement of 0.9–1.4 g·kg −1 ·day −1 has been suggested for those who are habituated to endurance exercise ( Kato et al., 2016 ; Meredith et al., 1989 ; Tarnopolsky et

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Bill I. Campbell, Danielle Aguilar, Laurin Conlin, Andres Vargas, Brad Jon Schoenfeld, Amey Corson, Chris Gai, Shiva Best, Elfego Galvan, and Kaylee Couvillion

Dietary protein is an essential component of the human diet. The constituent amino acids of dietary proteins are used to build body tissues, and thus protein consumption directly influences the accretion of muscle mass ( Atherton & Smith, 2012 ). Acute nitrogen balance studies indicate that

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Ben Desbrow, Nicholas A. Burd, Mark Tarnopolsky, Daniel R. Moore, and Kirsty J. Elliott-Sale

, less red blood cell expansion, and/or increased oxidation and/or repair/remodeling of structural/regulatory proteins could all contribute to deleterious effects on endurance performance. Although the dietary protein intake required to support nitrogen balance is similar among late middle-aged athletes