Nitrogen homoeostasis in man: diurnal changes in nitrogen excretion, leucine oxidation and whole body leucine kinetics during a reduction from a high to a moderate protein intake.
1. The adaptation of the diurnal cycle of nitrogen (N) homeostasis during a change in protein intake was investigated with diurnal measurements of N and leucine balance and turnover during a reduction from a high to a moderate protein intake in normal adults. 2. In experiment 1, during a 9 day period after a reduction from 1.82 to 0.77 g of protein day-1 kg-1, N excretion fell slowly at a similar rate in fed and fasted states so that the lowered intake was unable to replete any of the postabsorptive losses for 3 days. There was a marked negative N balance, which persisted throughout the study, although with a significant reduction in N losses in both fed and fasted states on day 4, balances during days 4-9 (-32.8 +/- 28.3 mg of N day-1 kg-1) were less negative than during days 1-3 (-79.1 +/- 60.4 mg of N day-1 kg-1). 3. In experiment 2, during a 14 day period after a reduction from 1.89 to 0.77 g of protein day-1 kg-1, [1-13C]leucine oxidation and turnover were measured by primed intravenous infusion, during fasting and feeding in subjects before and on days 3, 7 and 14 after the dietary change. Leucine oxidation fell by 32% (P < 0.05) on day 3 in the fed state and by 12% (P < 0.05) during fasting, falling further in each case by day 7 with improved balance.(ABSTRACT TRUNCATED AT 250 WORDS)
Quevedo
M R
MR
Nutrition Research Unit, London School of Hygiene and Tropical Medicine, St Pancras Hospital, U.K.
Price
G M
GM
Halliday
D
D
Pacy
P J
PJ
Millward
D J
DJ
D000222:Adaptation, Physiological; D000328:Adult; D002940:Circadian Rhythm / Q000502:physiology*; D004044:Dietary Proteins / Q000008:administration & dosage*; D005215:Fasting / Q000502:physiology; D005502:Food; D006706:Homeostasis / Q000502:physiology*; D006801:Humans; D007700:Kinetics; D007930:Leucine / Q000378:metabolism*; D008297:Male; D008875:Middle Aged; D009584:Nitrogen / Q000378:metabolism*; D010084:Oxidation-Reduction
D004044:Dietary Proteins; D007930:Leucine; D009584:Nitrogen