Difference of Plasma Amino Acids Following Casein or Soy Protein Intake: Significance for Differences of Serum Lipid Concentrations

There were significant differences of postprandial plasma concentrations for 8 amino acids (Cys, Val, Met, Leu, Tyr, Lys, Trp, and Arg) depending on whether pigs consumed a meal containing casein or isolated soy protein. The postprandial plasma amino acid pattern conformed with the amino acid composition of the dietary protein (except for Ser). The data, however, do not allow to conclude unambiguously, whether specific amino acids are responsible for the difference of serum cholesterol following casein or soy protein intake. Significant differences between casein- and soy-fed rats were observed regarding total and free plasma thyroxine and triiodothyronine concentrations. This observation can explain the accompanying different serum cholesterol concentrations. The different thyroid hormone concentrations were not paralleled by differences in TSH levels suggesting that dietary proteins affect thyroid function at the thyroid gland.