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Open Access Research

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

Abstract

Background

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.

Methods

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.

Results

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.

Conclusion

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.

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