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Nutrient Requirements and Optimal Nutrition

Resistance Training Reduces Fasted- and Fed-State Leucine Turnover and Increases Dietary Nitrogen Retention in Previously Untrained Young Men¹

³ Exercise Metabolism Research Group, Department of Kinesiology, and ⁴ Division of Gastroenterology, McMaster University, Hamilton, Ontario, Canada L8S 4K1

^* To whom correspondence should be addressed. E-mail: phillis{at}mcmaster.ca.

We aimed to determine the impact of intense resistance training, designed to increase lean body mass (LBM), on both fasted and fed whole body protein kinetics in untrained young men. Twelve healthy males (22 ± 2 y of age; BMI, 24.3 ± 2.4 kg/m²) participated in a 12-wk (5-d/wk) resistance training program. Before and after training, a primed constant infusion of [1-¹³C]leucine was used to measure whole body leucine turnover, protein breakdown, and nonoxidative leucine disposal in the fasted and fed states. Participants were studied during 5-d controlled diet periods that provided a moderate protein intake [1.4 g/(kg body wt · d)]. We estimated protein turnover and nitrogen balance. Training increased LBM (61.6 ± 6.9 vs. 64.8 ± 6.7 kg, P < 0.05). After training, whole body leucine turnover was reduced (P < 0.01) in both fasted (167 ± 18 vs. 152 ± 17) and fed (197 ± 23 vs. 178 ± 21) states [all values µmol/(kg LBM · h)]. Training-induced decreases (P < 0.01) in protein breakdown occurred in the fasted (165 ± 18 vs. 144 ± 17) and fed (111 ± 23 vs. 93 ± 20) states. Following training, nonoxidative leucine disposal was similarly reduced (P < 0.01) in the fasted (144 ± 18 vs. 126 ± 18) and fed (151 ± 20 vs. 133 ± 19) states. Nitrogen balance was more positive after training (13.7 ± 8.1 vs. 33.4 ± 12.5 g/(kg LBM · d), P < 0.01) indicating an increased retention of dietary nitrogen. Intense resistance training alters whole body protein kinetics in novice weightlifters regardless of feeding status. The increase in nitrogen balance after training demonstrates a more efficient utilization of dietary nitrogen, suggesting that protein requirements for novice weightlifters are not elevated.

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