Chris Villarosa 1
Optimal Protein Intake to
Maximize Muscle Protein Synthesis
Layne Norton’s Examination of Optimal Protein Intake and Frequency for Athletes
And the Role of the Amino Acid Leucine
Chris Villarosa
BC3123 Organic Chemistry
Lev Elson-Schwab
November 18, 2012
Chris Villarosa 2
Layne Norton is a renowned competitive powerlifter and natural bodybuilder as well as
highly respected coach. Among his enthusiasm for athleticism and competitiveness, Layne also
displays a passion for science having obtained a BS in Biochemistry and a PhD in Nutritional
Sciences (1). Fueled by his unique interests in the field of exercise and science, Layne’s thesis
emphasis was on muscle protein metabolism, and more specifically, the synthesis of skeletal
muscle and the role of leucine as an initiating determinant factor. His research concluded that the
meal content of the amino acid leucine is largely responsible for the anabolic effects of muscle
protein synthesis (MPS). In his examination of optimal protein intake and frequency, Layne
suggests that the MPS reponse to plasma leucine levels may remain elevated for as long as three
hours, but will decline despite nutritional or supplement interventions (2). The intent of this
paper is to present Layne Norton’s findings and interpretations of his research relevant to MPS.
Layne Norton’s discovery regarding the importance of the amino acid leucine and its effects on
MPS are essential in the sport nutrition world for its applications of macronutrient
recommendations and amino acid profile in an athlete’s diet.
Although the recommended daily allowance (RDA) suggests that dietary protein intake
only be met for metabolic requirements, the 0.8g/kg of protein that is necessary to maintain
short-term nitrogen balance may not be applicable for all individuals (3). Layne attributes this
statement by refuting the general consensus that “meeting the minimum requirements for the
most limiting amino acids in protein will lead to a plateau of nitrogen retention and any further
increase in plasma amino acids would stimulate increased oxidation and elimination of excess
amino acids.” Under this assumption, any additional dietery intake of amino acids would be
irrelevant; the common misconception. Layne’s research begs to differ. His discovery suggests
that although excessive amino acid oxidation may take place, these amino acids may additionally
initiate signaling necessary for MPS. Layne concluded that the initiation of the MPS pathway is
largely due to plasma leucine levels and that RDA for protein intake is insufficient for an athlete
whose goals are to maintain or gain lean muscle tissue (2).
Denouncing overall gram-per-day protein intake, Layne suggests that the distribution of
protein throughout the day is highly relevant to MPS. His research suggests a large correlation
between the protein content of a meal, specifically the leucine concentration of the protein within
that meal, and its relationship to anabolic protein synthesis. As his research shows, leucine has
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been proposed to account for the facilitation of signaling MPS. In Layne’s lab, an isocaloric
isonitrogenous diet manipulated by whey protein or wheat gluten demonstrated a difference in
post-prandial plasma leucine content and variations of MPS stimulation suggesting that amino
acid profile largely plays a role in determining an anabolic protein-synthesizing signal. This
specific MPS signal is proposed to be the mammalian target of rapamaycin (mTOR) signaling
pathway (2, 4).
Layne’s work suggests that mTOR stimulation via leucine initiates translation by
increasing the rate of eukaryotic initiation factor 4F complex (eIF4F) which 43S preintiation
complex must need present in order to bind to mRNA. This rate-limiting step is facilitated by
increased leucine-induced phosphorylation of an inhibitory protein, eukaryotic initiation factor
4E binding protein 1 (4E-BP1). 4E-BP1 binds to eukaryotic initiation factor 4E (eI4FE) and
inhibits the formation of a complex produced by the association of eI4FE and eukaryotic
initiation factor 4G (eIF4G). The product of 4E-BP1 phosphorylation results in the ability of
eIF4F and eIF4G to form the eIF4F complex. Additionally, Layne found that mTOR activation
via leucine also assists in the phosphorylation of p70 S6 kinase (S6K), a ribosomal protein that
increases selective mRNA translation specific to the mechanism of MPS which also dictates
overall MPS capacity of a cell. These findings demonstrate the importance of leucine and MPS.
After examining the effects of leucine and MPS, Layne determines optimal values of
leucine content in a meal as well as meal frequency to maximize the MPS response. Based on the
research of others, Layne concludes that 3g of leucine is sufficient for a MPS reponse. Layne and
his team then demonstrate the effects of a complete meal on MPS. After an analysis of plasma
and intramuscular leucine concentrations after a meal, Layne concludes that although a purified
amino acid solution containing exclusively leucine or a combination of leucine and other
essential amino acids may heighten the anabolic MPS response for 2 hours, a complete meal
containing similar leucine values may prolong the anabolic response for up to 3 hours despite a
reduction in leucine concentrations after a peak between 45-180 minutes. Despite a reduction
following its peak, leucine concentrations remained above baseline for five hours while MPS
returned to baseline values after the 3-hours leucine concentration peak. Layne also concludes
that despite dietary interventions that increase plasma leucine levels, mTOR signaling and MPS
duration was not increased in efforts to sustain MPS. Based on this phenomenon, Layne suggests
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a refractory period that follows peaked MPS (2); a mechanism in which Layne can only currently
make proposals to, but not make definite conclusions about.
In conclusion, Layne’s research demonstrates the importance of the branch-chain amino
acid, leucine and its role in contributing to MPS. In summary, Layne’s contribution to science
and discoveries suggest: protein intake is strongly correlated to leucine density in a given meal,
dietary leucine and increased plasma leucine levels increase mRNA translation permissive for
MPS, optimal leucine levels are about 3g per meal, and any additional supplemental or dietary
interventions to increase MPS duration are irrelevant in between four to six hour intervals post
prandially.
Without a doubt, knowledgeable athletes and dieticians can utilize Layne’s research,
results, and discoveries to enhance performance or body composition goals for themselves or
their clients. Collectively, Layne’s research provides a solid irrefutable foundation for optimal
protein utilization in the diet. Where the generic “calories in vs. calories out” mentality may
resound, this research simply denounces any false perception that all calories are created equal.
Furthermore, the RDA of 0.8g/kg protein proves its irrelevance through Layne’s research in a
population that desires lean mass gains or muscular performance enhancement.
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References
1. About biolayne. (2011). Retrieved from http://www.biolayne.com/about/
2. Norton, L. E. (2009). Optimal protein intake to maximize muscle protein synthesis. Argo food
industry hi-tech, 20(2), 54-57. Retrieved from http://www.biolayne.com/wpcontent/uploads/Norton-J-Ag-Food-Ind-Hi-Tech-2008.pdf
3. Campbell, B. (2007). International society of sports nutrition position stand: protein and
exercise. 4(8), Retrieved from http://www.jissn.com/content/pdf/1550-2783-4-8.pdf
4. Norton, L. E. (2006 ). Leucine regulates translation initiation of protein synthesis in skeletal
muscle after exercise. The journal of nutrition, 136(2), 533S-537S. Retrieved from
http://jn.nutrition.org/content/136/2/533S.long