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United States Department of Agriculture

Agricultural Research Service

Title: Response of Hepatic Proteins to the Lowering of Habitual Dietary Protein to the Recommended Safe Level of Intake

Authors
item Afolabi, Paul - UNIVERSITY OF SOUTHAMPTON
item Jahoor, Farook
item Gibson, Neil - UNIVERSITY OF SOUTHAMPTON
item Jackson, Alan - UNIVERSITY OF SOUTHAMPTON

Submitted to: American Journal of Physiology - Endocrinology and Metabolism
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 21, 2004
Publication Date: August 1, 2004
Citation: Afolabi, P.A., Jahoor, F., Gibson, N.R., Jackson, A.A. 2004. Response of heptic proteins to the lowering of habitual dietary protein to the recommended safe level of intake. American Journal of Physiology-Endocrinology and Metabolism. 287:E327-E330.

Interpretive Summary: The FAO/WHO recommended safe level of dietary protein intake for healthy adults is 0.75 g/kg/d. However, most Western populations' habitual intakes range from 1 to 1.5 g/kg/d. Hence it is not known whether healthy individuals will be able to maintain the synthesis of all body proteins, especially those with very fast turnover rates such as the plasma nutrient transport proteins and the positive acute-phase proteins that play an important role in host defense during infections, inflammation, and injuries. This study was performed to determine whether healthy adults could maintain the concentration of 6 proteins and rates of synthesis of two nutrient transport and one positive acute-phase proteins when consuming the recommended protein intake of 0.75 g/kg/d. A stable isotope infusion protocol was used to determine the synthesis rates of the proteins in 12 young adults on three occasions during a reduction of their habitual protein intake from 1.13 to 0.75 g/kg/d for 10 days. The plasma concentration of only 1 of the 6 proteins, HDL-apoA1, fell. The synthesis rates of the 2 nutrient transport proteins decreased significantly also. The results indicate that when normal adults consume the recommended safe level of protein, there is a slower rate of turnover of some nutrient transport proteins than on their habitual diet. Hence, healthy individuals consuming this amount of protein may be less able to mount an adequate metabolic response to a stressful stimulus.

Technical Abstract: The plasma concentrations of albumin, HDL apolipoprotein A1 (apoA1), retinol-binding protein (RBP), transthyretin (TTR), haptoglobulin, and fibrinogen were measured, and a stable isotope infusion protocol was used to determine the fractional and absolute synthesis rates of RBP, TTR, and fibrinogen in 12 young adults on three occasions during a reduction of their habitual protein intake from 1.13 to 0.75 g x kg(-1) x day(-1) for 10 days. This study was performed to determine whether healthy adults could maintain the rates of synthesis of selected nutrient transport and positive acute-phase proteins when consuming a protein intake of 0.75 g x kg(-1) x day(-1). During the lower protein intake, the plasma concentration of all the proteins, other than HDL-apoA1, remained unchanged. HDL-apoA1 concentration was significantly reduced (P < 0.05) after 3 days of the lower protein intake, but not at 10 days. The rates of synthesis of RBP and TTR declined significantly (P < 0.05), whereas the rate of synthesis of fibrinogen remained unchanged. The results indicate that when normal adults consume the recommended safe level of protein, 0.75 g x kg(-1) x day(-1), there is a slower rate of turnover of nutrient transport proteins than on their habitual diet. Hence, healthy individuals consuming this amount of protein may be less able to mount an adequate metabolic response to a stressful stimulus.

Last Modified: 7/28/2014
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