The 24-h whole body leucine and urea kinetics at normal and high protein intakes with exercise in healthy adults.
In healthy adult men adapted to a diet/exercise regimen for 6 days, the effects of small, frequent meals supplying daily protein intakes of 1 (n = 8) or 2.5 g . kg-1 . day-1 (n = 6) on leucine oxidation, urea production, and whole body protein synthesis (PS) and degradation (PD) have been compared with the use of a 24-h continuous intravenous [13C]leucine and [15N,15N]urea infusion protocol. Two 90-min periods of exercise (approximately 50% maximal O2 consumption) were included during the fasting and the fed periods of the 24-h day. Subjects were determined to be at approximate energy, nitrogen, and leucine balances on both diets. Increased protein intake raised the urea production rate; the absolute rate of urea hydrolysis was the same on both diets. When the first-pass splanchnic uptake of leucine was taken to be 25% of intake, PS was stimulated by feeding (after an overnight fast) at both protein intake levels (P < 0.05 and P < 0.01), whereas PD declined significantly (P < 0.01) at both protein levels. Protein gain at a high protein intake appears to be the result of both a stimulation of PS and a marked decline in PD, whereas at a less generous intake, the gain appears to be a result of a fall in PD with a less evident change in PS. Exercise moderately decreased PS during and/or immediately after exercise at each protein level, and there was a postexercise-induced increase (P < 0.01) in PD, which was more dramatic when feeding was at the higher protein intake level.
Forslund
A H
AH
Department of Nutrition, Uppsala University, S-75237 Uppsala, Sweden.
Hambraeus
L
L
Olsson
R M
RM
El-Khoury
A E
AE
Yu
Y M
YM
Young
V R
VR
D000328:Adult; D000704:Analysis of Variance; D002247:Carbon Isotopes; D002940:Circadian Rhythm; D004044:Dietary Proteins; D004435:Eating; D015444:Exercise / Q000502:physiology*; D005215:Fasting; D006801:Humans; D007700:Kinetics; D007930:Leucine / Q000378:metabolism*; D008297:Male; D009587:Nitrogen Isotopes; D010084:Oxidation-Reduction; D012016:Reference Values; D013997:Time Factors; D014508:Urea / Q000378:metabolism*
D002247:Carbon Isotopes; D004044:Dietary Proteins; D009587:Nitrogen Isotopes; D014508:Urea; D007930:Leucine