The biological effects of soy and casein meals in interorgan amino acid metabolism in the pig as a model for man
1998
Deutz, N.E.P. | Soeters, P.B. (Maastricht Univ. (Netherlands). Dept. of Surgery)
Studying metabolism during a meal provides important information about how nutrients are taken up and used in the different metabolic routes. For that purpose, a model using conscious pigs was developed which enables the measurement of organ metabolism (for example gut, liver, muscle, kidney). On the basis of several studies with this model, we formulated the hypothesis that intestinal metabolism of absorbed nutrients determines the biological value of the absorbed protein. As an example, we studied the biological effects of casein and soy meals on the contribution of individual amino acids to net protein retention and amino acid kinetics in gut, liver and muscle in healthy pigs. Iso-nitrogenous enteral nutrition (maltodextrin with either casein or soy protein) was given to conscious, healthy female pigs (n=12). A primed-constant infusion protocol with L-[ring-2,6-3H]Phenylalanine (PHE), L-[3,4-3H]Valine (VAL) and [15N-15N]Urea was used to measure amino acid and urea kinetics in gut, liver and muscle. Measurements were made post-absorption and 2-6 h after initiation of the enteral nutrition. It was found that during the meal, the appearance of amino acids into the portal vein and the uptake by the liver was lower with casein, while muscle uptake was comparable. Gut protein synthesis was lower with soy, but did not reach statistical significance. Liver protein synthesis and degradation were higher with casein, while in muscle soy stimulated protein turnover. Liver urea production did not change by nutrition with casein, while it increased with soy. The results suggest that soy and casein protein meals have different influences on organ amino acid and urea metabolism, and consequently the quality of soy protein should be considered inferior to that of casein protein.
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