Consumption of fluid skim milk promotes greater muscle protein accretion after resistance exercise than does consumption of an isonitrogenous and isoenergetic soy-protein beverage.
BACKGROUND
Resistance exercise leads to net muscle protein accretion through a synergistic interaction of exercise and feeding. Proteins from different sources may differ in their ability to support muscle protein accretion because of different patterns of postprandial hyperaminoacidemia.


OBJECTIVE
We examined the effect of consuming isonitrogenous, isoenergetic, and macronutrient-matched soy or milk beverages (18 g protein, 750 kJ) on protein kinetics and net muscle protein balance after resistance exercise in healthy young men. Our hypothesis was that soy ingestion would result in larger but transient hyperaminoacidemia compared with milk and that milk would promote a greater net balance because of lower but prolonged hyperaminoacidemia.


METHODS
Arterial-venous amino acid balance and muscle fractional synthesis rates were measured in young men who consumed fluid milk or a soy-protein beverage in a crossover design after a bout of resistance exercise.


RESULTS
Ingestion of both soy and milk resulted in a positive net protein balance. Analysis of area under the net balance curves indicated an overall greater net balance after milk ingestion (P < 0.05). The fractional synthesis rate in muscle was also greater after milk consumption (0.10 +/- 0.01%/h) than after soy consumption (0.07 +/- 0.01%/h; P = 0.05).


CONCLUSIONS
Milk-based proteins promote muscle protein accretion to a greater extent than do soy-based proteins when consumed after resistance exercise. The consumption of either milk or soy protein with resistance training promotes muscle mass maintenance and gains, but chronic consumption of milk proteins after resistance exercise likely supports a more rapid lean mass accrual.
Wilkinson
Sarah B
SB
Exercise Metabolism Research Group, Department of Kinesiology, McMaster University, Hamilton, Canada.
Tarnopolsky
Mark A
MA
Macdonald
Maureen J
MJ
Macdonald
Jay R
JR
Armstrong
David
D
Phillips
Stuart M
SM
D000328:Adult; D000596:Amino Acids / Q000097:blood*; D019540:Area Under Curve; D001823:Body Composition / Q000187:drug effects / Q000502:physiology; D018592:Cross-Over Studies; D004044:Dietary Proteins / Q000008:administration & dosage / Q000378:metabolism*; D006801:Humans; D008297:Male; D008894:Milk Proteins / Q000008:administration & dosage / Q000378:metabolism*; D009124:Muscle Proteins / Q000096:biosynthesis*; D018482:Muscle, Skeletal / Q000254:growth & development / Q000378:metabolism; D030262:Soybean Proteins / Q000008:administration & dosage / Q000378:metabolism*; D014891:Weight Lifting / Q000502:physiology
D000596:Amino Acids; D004044:Dietary Proteins; D008894:Milk Proteins; D009124:Muscle Proteins; D030262:Soybean Proteins