Impact of habituated dietary protein intake on fasting and postprandial whole-body protein turnover and splanchnic amino acid metabolism in elderly men: a randomized, controlled, crossover trial
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Background: Efficacy of protein absorption and subsequent amino acid utilization may be reduced in the elderly. Higher protein intakes have been suggested to counteract this.
Objectives: We aimed to elucidate how habituated amounts of protein intake affect the fasted state of, and the stimulatory effect of a protein-rich meal on, protein absorption, whole-body protein turnover, and splanchnic amino acid metabolism.
Methods: Twelve men (65-70 y) were included in a double-blinded crossover intervention study, consisting of a 20-d habituation period to a protein intake at the RDA or a high amount [1.1 g . kg lean body mass (LBM)(-)(1) . d(-1) or >2.1 g . kg LBM-1 . d(-1), respectively], each followed by an experimental trial with a primed, constant infusion of D-8-phenylalanine and D-2-tyrosine. Arterial and hepatic venous blood samples were obtained after an overnight fast and repeatedly 4 h after a standardized meal including intrinsically labeled whey protein concentrate and calcium-caseinate proteins. Blood was analyzed for amino acid concentrations and phenylalanine and tyrosine tracer enrichments from which whole-body and splanchnic amino acid and protein kinetics were calculated.
Results: High (compared with the recommended amount of) protein intake resulted in a higher fasting whole-body protein turnover with a resultant mean +/- SEM 0.03 +/- 0.01 mu mol . kg LBM-1 . min(-1) lower net balance (P <0.05), which was not rescued by the intake of a protein-dense meal. The mean +/- SEM plasma protein fractional synthesis rate was 0.13 +/- 0.06%/h lower (P <0.05) after habituation to high protein. Furthermore, higher fasting and postprandial amino acid removal were observed after habituation to high protein, yielding higher urea excretion and increased phenylalanine oxidation rates (P <0.01).
Conclusions: Three weeks of habituation to high protein intake (>2.1 g protein . kg LBM-1 . d(-1)) led to a significantly higher net protein loss in the fasted state. This was not compensated for in the 4-h postprandial period after intake of a meal high in protein.
Originalsprog | Engelsk |
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Tidsskrift | American Journal of Clinical Nutrition |
Vol/bind | 112 |
Udgave nummer | 6 |
Sider (fra-til) | 1468-1484 |
ISSN | 0002-9165 |
DOI | |
Status | Udgivet - 2020 |
ID: 256981923