AJP - Endocrinology and Metabolism, Vol 268, Issue 6 E1143-E1153, Copyright © 1995 by American Physiological Society

ARTICLES

Effects of resistance training and dietary protein intake on protein metabolism in older adults

W. W. Campbell, M. C. Crim, V. R. Young, L. J. Joseph and W. J. Evans
Human Physiology Laboratory, US Department of Agriculture Jean Mayer Human Nutrition Research Center on Aging at Tufts University, Boston 02111, USA.

Nitrogen (N) balance, fed-state leucine kinetics, and urinary 3-methylhistidine (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 +/- 0.02 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) and positive for HP (13.6 +/- 1.0 mg N.kg-1.day-1). N retention increased 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 efficiency of N retention. LP had decreased leucine flux (P < 0.001), oxidation (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 in both diet groups (P < 0.05) and was associated mainly with an increase 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-creatinine ratio, P < 0.01). Diet-related differences in protein metabolism 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.

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