Whole-body protein turnover and nitrogen balance in young children at intakes of protein and energy in the region of maintenance.
Nitrogen balance and whole-body protein turnover were measured in children aged about one year taking diets which provided 1.7 or 0.7 g milk protein/kg/d at three levels of metabolizable energy, 80, 90 and 100 kcal/kg/d. All the children were in positive nitrogen balance at all levels of energy intake on 1.7 g protein/kg/d. Nitrogen equilibrium was maintained on 0.7 g protein/kg/d when the energy intake exceeded 90 kcal/kg/d, but on 80 kcal/kg/d nitrogen balance was negative. Whole-body protein turnover was measured from the enrichment in urinary ammonia following a continuous infusion of 15N-glycine. The variation between individuals on the same diet was significantly greater than the variation within individuals at different levels of energy intake. For the group as a whole protein synthesis on 1.7 g protein/kg/d was 0.74, 0.75 and 0.87 g N/kg/d on 100, 90 and 80 kcal/kg/d respectively; whereas on 0.7 g protein/kg/d it was 0.37, 0.38 and 0.40 g N/kg/d. These results show that over this range of intakes protein synthesis decreased as dietary protein fell, but tended to increase as energy intake fell.
D000641:Ammonia / Q000652:urine; D001827:Body Height; D001835:Body Weight; D003404:Creatinine / Q000652:urine; D004044:Dietary Proteins / Q000008:administration & dosage*; D002149:Energy Intake; D006801:Humans; D007223:Infant; D007225:Infant Food / Q000032:analysis; D008297:Male; D008762:Methylhistidines / Q000652:urine; D009584:Nitrogen / Q000378:metabolism*; D011506:Proteins / Q000378:metabolism*; D014508:Urea / Q000652:urine
D004044:Dietary Proteins; D008762:Methylhistidines; D011506:Proteins; D000641:Ammonia; D014508:Urea; D003404:Creatinine; C028118:3-methylhistidine; D009584:Nitrogen