Whole body protein kinetics, calculated using a phenylalanine tracer, in critically ill mechanically ventilated neurosurgical patients (n = 16) who received normocaloric and hypocaloric intravenous nutrition in random order during two consecutive days. Patients were randomized to receive normocaloric before hypocaloric (filled symbols), or hypocaloric before normocaloric (open symbols) nutrition. (A) Whole-body protein synthesis; (B) whole-body protein degradation; (C) phenylalanine oxidation; (D) whole-body protein balance. P-values are for paired comparisons. Phe, phenylalanine. Red lines indicate mean values.