EFFECTS OF RESISTANCE TRAINING AND DIETARY-PROTEIN INTAKE ON PROTEIN-METABOLISM IN OLDER ADULTS

Nitrogen (N) balance, fed-state leucine kinetics, and urinary 3-methyl histidine (3-MeH) excretion were examined in 12 men and women, aged 56 -80 yr, before and during 12 wk of resistance training (RT). Subjects were randomized to groups that consumed diets providing either 0.80 +/ - 0.02 g protein . kg(-1). day(-1) (lower protein, LP) or 1.62 +/- 0.0 2 g protein . kg(-1). day(-1) (higher protein, HP). At baseline, mean N balance was negative for LP (-4.6 +/- 3.4 mg N . kg(-1). day(-1)) an d positive for HP (13.6 +/- 1.0 mg N . kg(-1). day(-1)). N retention i ncreased similarly in LP and HP at the 11th wk of RT by 12.8 and 12.7 mg N . kg(-1). day(-1), respectively. Thus LP had an increased efficie ncy of N retention. LP had decreased leucine flux (P < 0.001), oxidati on (P < 0.001), and uptake for protein synthesis (P < 0.02), relative to HP, both at baseline and after RT. Leucine flux increased with RT i n both diet groups (P < 0.05) and was associated mainly with an increa se in protein synthesis in LP (91% of change in flux) and an increase in oxidation in HP (72% of change in flux; RT-diet interaction, P < 0. 05). RT increased actomyosin protein breakdown (increased 3-MeH-to-cre atinine ratio, P < 0.01). Diet-related differences in protein metaboli sm did not influence body composition changes with RT. These data show that the efficiency of N retention and protein utilization during RT is higher in older subjects who consume 0.8 vs. 1.6 g protein . kg(-1) . day(-1) dietary protein.