Protein metabolic effects of a prolonged fast and hypocaloric refeeding.
In a study of the mechanism of adaptation to protein deficiency, 10 moderately obese women underwent a 3-wk fast followed by random allocation to a 1-wk refeeding regimen providing 80 g carbohydrate or protein. Protein metabolism was studied by means of nitrogen (N) balance, urinary 3-methylhistidine excretion, and postabsorptive plasma leucine flux using L-[1-13C]leucine infusions. After the 3-wk fast, plasma leucine flux and 3-methylhistidine excretion both decreased by 31% from control diet values (P less than 0.01), and N balance was -5.9 g/day. After protein refeeding, N balance was positive (+1.7 g/day, P less than 0.05) whereas leucine flux was unchanged from prolonged fasting values. After carbohydrate refeeding, N balance improved to -3.1 g N/day, whereas leucine flux decreased by a further 18% (P less than 0.05). Protein and carbohydrate refeeding were associated with further 23 and 31% reductions of 3-methylhistidine excretion compared with prolonged fasting (P less than 0.05). The results support the hypothesis that improved efficiency of protein retention in starvation is intimately associated with a decreased rate of protein turnover.
McGill Nutrition and Food Science Centre, Department of Medicine, Royal Victoria Hospital, Montreal, Quebec, Canada.
L J
LJ
Hoffer
R A
RA
Forse
D020155:3-Hydroxybutyric Acid; D001786:Blood Glucose / Q000378:metabolism; D002247:Carbon Isotopes; D004038:Diet, Reducing; D004040:Dietary Carbohydrates; D004044:Dietary Proteins; D002149:Energy Intake; D005215:Fasting; D005230:Fatty Acids, Nonesterified / Q000097:blood; D005260:Female; D006801:Humans; D006885:Hydroxybutyrates / Q000097:blood; D007328:Insulin / Q000097:blood; D007553:Isotope Labeling / Q000379:methods; D007930:Leucine / Q000097:blood; D009584:Nitrogen / Q000378:metabolism; D009765:Obesity / Q000378:metabolism*; D011506:Proteins / Q000378:metabolism*; D011897:Random Allocation; D013974:Thyroxine / Q000097:blood; D014285:Triiodothyronine, Reverse / Q000097:blood
D001786:Blood Glucose; D002247:Carbon Isotopes; D004040:Dietary Carbohydrates; D004044:Dietary Proteins; D005230:Fatty Acids, Nonesterified; D006885:Hydroxybutyrates; D007328:Insulin; D011506:Proteins; D014285:Triiodothyronine, Reverse; D007930:Leucine; D009584:Nitrogen; D013974:Thyroxine; D020155:3-Hydroxybutyric Acid