Effects of resistance training and dietary protein intake on protein metabolism in older adults.
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.
Campbell
W W
WW
Human Physiology Laboratory, US Department of Agriculture Jean Mayer Human Nutrition Research Center on Aging at Tufts University, Boston 02111, USA.
Crim
M C
MC
Young
V R
VR
Joseph
L J
LJ
Evans
W J
WJ
D000368:Aged; D000369:Aged, 80 and over; D001823:Body Composition; D004044:Dietary Proteins; D002149:Energy Intake; D005081:Exercise Therapy; D005260:Female; D006801:Humans; D007930:Leucine / Q000378:metabolism*; D008297:Male; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000033:anatomy & histology; D010807:Physical Endurance; D011506:Proteins / Q000378:metabolism*; D012044:Regression Analysis
D004044:Dietary Proteins; D011506:Proteins; D007930:Leucine