Protein distribution affects muscle mass based on differences in
postprandial muscle protein synthesis and plasma leucine in rats
L.E. Norton1, G.J. Wilson1, D.K. Layman1 ,C.J. Moulton1, and P.J. Garlick2
1Dept. Food Science & Human Nutrition and 2Animal Sciences,
- University of Illinois at Urbana-Champaign, Urbana, IL
Americans consume small servings of protein early in the day, with over 60% of
daily protein intake coming at dinner. How protein distribution affects muscle
mass is uncertain. This study evaluated effects of isonitrogenous whey protein
diets in which the meal distribution of protein was either equal at breakfast,
lunch, and dinner (16% protein at each) or unevenly distributed consisting of 8%
whey protein at breakfast and lunch, and 27.5% at dinner. Adult rats (300g) were
fed 3 meals/d for 11 wk. At 2 and 11wk, rats were sacrificed after a 13hr fast or
90min after consuming the breakfast meal. Measurements included skeletal
muscle weights, plasma insulin, glucose, amino acids, muscle protein synthesis
(MPS) determined by D5-Phe incorporation and phosphorylation activation of
initiation factors 4E-BP1 and S6K. Results showed that the equally distributed
whey protein group had significantly greater postprandial MPS after the
breakfast meal and larger gastrocnemius muscle mass than the unequally
distributed treatment. MPS responses were closely related with changes in
plasma leucine and phosphorylation of 4E-BP1 and S6K. These results suggest
that protein distribution is a critical factor in determining efficiency of protein
utilization and optimization of skeletal muscle mass.
Plasma Leucine
Fractional Rate MPS % Per Day
Theoretical Model for Maximal stimulations of muscle protein
synthesis throughout the day in humans (adapted from reference 2).
Research Question
Support: American Egg Board/Egg Nutrition Center
4E-BP1 % Phosphorylation
S6K % Phosphorylation
Does protein distribution makes a difference in long term body composition and
muscle weight?
• Increases in plasma leucine have been shown to be a
critical trigger for increasing translation initiation, and muscle
protein synthesis (MPS) (1).
• We have identified a meal threshold for leucine consumption
necessary to increase plasma leucine, and stimulate
translation initiation and MPS (>60 mg leucine) (1).
• Americans consume small servings of protein early in the
day, with over 60% of daily protein intake coming at dinner.
• These small meals consumed early in the day may be below
the optimal threshold for stimulating MPS. The result may be
maximal stimulation of muscle protein synthesis at dinner, with
minimal stimulations for the remainder of the day.
• We propose that equal meal distributions of dietary protein
which all meet the previously mentioned “leucine threshold”
(>60 mg of leucine), will optimize muscle protein synthesis at
all meals, and result in improved long term muscle size.
Grams Food
%Carbohydrate : Whey Protein Isolate : Fat
Equally Distributed Whey
Unequally Distributed Whey 62:8:30
Leucine content (mg) (259 mg total in both conditions)
300 gram Male Sprague Dawley rats
Measurements at 10 weeks:
-Rats sacrificed in fasted state and 90 minutes post meal.
-L-[2H5]phenylalanine was injected via tail vein 10 minutes prior to sacrifice for
measurement of MPS.
-MPS was determined by GCMS analysis.
-Plasma amino acids were measured by fluorescence detection on HPLC.
-S6K and 4E-BP1 phosphorylation were measured by western blots.
Muscle Weight
Liver Weight
MPS responses at the breakfast meal were closely related to changes in
phosphorylation of 4E-BP1, S6K, and plasma leucine.
Equal distributions of protein throughout the day that reach the minimum
threshold for stimulating MPS are critical for long term muscle mass.
Unequal distributions of protein throughout the day increase liver size,
perhaps to accommodate the large dinner protein load.
(1.) Norton, L.E., Wilson, G.J., Rupassara, I., Garlick, P.J., and Layman, D.K.
Leucine contents of isonitrogenous protein sources predict post prandial
skeletal muscle protein synthesis in rats fed a complete meal. FASEB.
2009. 227.4
(2.) Paddon-Jones D, Rasmussen BB. Dietary protein recommendations and
the prevention of sarcopenia. Curr Opin Clin Nutr Metab Care 2009, 12:8690.