The effect of whole protein and L-amino acid ingestion on plasma amino acid (PAA) and urea nitrogen (UN) concentrations was investigated. Ten males ingested equivalent amounts of nitrogen as (trial 1) cottage cheese, (trial 2) an L-amino acid mixture, (trial 3) cottage cheese and L-amino acids. Mean changes in total PAA between trials 1 (342 μmol/liter) and 2 (719 μmol/liter) and trials 1 (342 μmol/liter) and 3 (981 μmol/liter) at 30 min and trials 1 (547 μmol/liter) and 3 (143 μmol/liter) at 150 min differed significantly. Mean changes in essential PAA between trials 1 (180 μmol/liter) and 2 (420 μmol/liter) and trials 1 (180 μmol/liter) and 3 (500 μmol/liter) at 30 min differed significantly. Mean changes in essential PAA between trials 1 (247 μmol/liter) and 3 (334 μmol/liter) at 60 min and between trials 1 (252 μmol/liter) and 3 (80 μmol/liter) at 150 min differed significantly. Mean increments in total and essential PAA were higher and peaked faster but decreased more quickly after trials 2 and 3 than after trial 1. Mean changes in plasma UN did not differ between trials. Ingestion of either L-amino acids, whole protein or the mixture of L-amino acids and whole protein was equally effective in increasing total PAA over 4 hr. (Journal of Parenteral and Enteral Nutrition15:48-53, 1991)
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