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Leucine content of dietary proteins is a determinant of postprandial skeletal muscle protein synthesis in adult rats

Layne E Norton12*, Gabriel J Wilson12, Donald K Layman12*, Christopher J Moulton12 and Peter J Garlick123

Author Affiliations

1 Division of Nutritional Sciences, University of Illinois at Urbana-Champaign, Urbana, IL, 61801, USA

2 Department of Food Science and Human Nutrition, University of Illinois at Urbana-Champaign, Urbana, IL, 61801, USA

3 Department of Animal Sciences, University of Illinois at Urbana-Champaign, Urbana, IL, 61801, USA

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Nutrition & Metabolism 2012, 9:67  doi:10.1186/1743-7075-9-67

Published: 20 July 2012



Leucine (Leu) regulates muscle protein synthesis (MPS) producing dose-dependent plasma Leu and MPS responses from free amino acid solutions. This study examined the role of Leu content from dietary proteins in regulation of MPS after complete meals.


Experiment 1 examined 4 protein sources (wheat, soy, egg, and whey) with different Leu concentrations (6.8, 8.0, 8.8, and 10.9% (w/w), respectively) on the potential to increase plasma Leu, activate translation factors, and stimulate MPS. Male rats (~250 g) were trained for 14 day to eat 3 meals/day consisting of 16/54/30% of energy from protein, carbohydrates and fats. Rats were killed on d14 either before or 90 min after consuming a 4 g breakfast meal. Experiment 2 compared feeding wheat, whey, and wheat + Leu to determine if supplementing the Leu content of the wheat meal would yield similar anabolic responses as whey.


In Experiment 1, only whey and egg groups increased post-prandial plasma Leu and stimulated MPS above food-deprived controls. Likewise, greater phosphorylation of p70 S6 kinase 1 (S6K1) and 4E binding protein-1 (4E-BP1) occurred in whey and egg groups versus wheat and soy groups. Experiment 2 demonstrated that supplementing wheat with Leu to equalize the Leu content of the meal also equalized the rates of MPS.


These findings demonstrate that Leu content is a critical factor for evaluating the quantity and quality of proteins necessary at a meal for stimulation of MPS.

Protein quality; Branched-chain amino acids; Whey protein; Insulin; mTOR