Protein consumption following aerobic exercise increases whole-body protein turnover in older adults
 
 
Journal Title (Medline/Pubmed accepted abbreviation): Appl. Physiol. Nutr. Metab.
Year: 2010
Volume: 35
Number:
Page numbers: 583-590
doi (if applicable): 10.1139/H10-047

Summary of Background and Research Design

Background: It is common for lean body mass to decrease as a person ages, which can lead to detrimental alterations in body composition and increased risk for chronic diseases. Ingestion of protein post-workout has been shown to be more effective in increasing whole body protein turnover than carbohydrates in younger adult populations undergoing resistance training. However, the effects of protein versus carbohydrate on whole body protein turnover have not been evaluated in an older adult population undertaking a more aerobic and, perhaps, more realistic exercise type for this population, such as walking.
 
Whole body protein turnover (WBPT): Both whole body protein synthesis and whole body protein breakdown are important for maintaining quality and quantity of lean body mass. The ability to remodel damaged proteins is necessary to maintain the integrity and function of their resident tissues.

Hypothesis/Research Question:A protein drink would increase the rate of whole body protein turnover during the first 4 h of postexercise recovery more than an isocaloric carbohydrate drink.

Subjects: 12 healthy, nonobese nonsmokers, 4 women (age 58 ± 1 y) and 8 men (age 60 ± 5 y), that do not habitually exercise. Mean body weights were 84 kg and 67 kg for males and females, respectively.

Experimental design:double-blind, crossover design

Treatments and protocol:
Before the protocol, the subjects' VO2max was determined. Subjects cycled on a stationary bicycle at 50 W initially, and the power increased 30 W per min for men and 20 W per min for women until volitional (self-determined) exhaustion. Maximum power ( Wmax ) was recorded and VO2max was determined by the average rate of oxygen uptake over the last min of their workout.
On the day of testing, subjects arrived at the laboratory after an overnight fast. One venous catheter was inserted into each arm, one to infuse tracers [NaH13CO3 (35 mg priming bolus) and 1-13C leucine (60 mg prime, 75 mg/hr continuous)] and the other to collect venous blood. Subjects rested for 2 hrs to establish an isotope steady state. Oxidation of leucine (Rox) was quantified by excretion of 13CO2 in breath, while the rate of leucine appearance (Ra) was tracked by measurement of labeled leucine in plasma. The assumption was made that Ra was equivalent to the rate of leucine disappearance (Rd). Nonoxidative leucine disposal (NOLD) was calculated as the difference between Ra and Rox. After a 2-h rest period to allow for isotope equilibration, the subjects performed 1 hr of cycling at 40% Wmax (which turned out to be about 50% VO2max). Breath was sampled every 15 min. Immediately after exercise, the experimental beverage was consumed (CHO beverage was 60 g maltodextrin and the PRO beverage was 40 g maltodextrin and 20 g whey protein) and the participants rested for 4 hrs while breath and blood samples were collected.

Summary of research findings:
  • The PRO beverage resulted in greater levels of leucine and essential and nonessential amino acids than the CHO beverage at 0.5 and 4 h post-exercise; these levels were no longer different at 4 h postexercise.
  • From 2-4 h postexercise, the PRO beverage resulted in significant increases (P = 0.001) in Ra , Rox, and NOLD (2.51 ± 0.55, 0.78 ± 0.37, and 1.71 ± 0.44 µmol/kg/min, respectively) versus the CHO beverage (1.81 ± 0.27, 0.33 ± 0.14, and 1.47 ± 0.25 µmol/kg/min, respectively).

Interpretation of findings/Key practice applications:

Low to moderate exercise (ex. walking) followed by a high protein beverage increases whole body protein turnover relative to a carbohydrate-only beverage in the elderly. It is thought that this improved remodeling of body proteins with the PRO drink versus CHO drink may contribute to better health of tissues such as skeletal muscle. It was notable that this effect was observed even with relatively low intensity exercise. It would be interesting to see the magnitude of this effect following more intense resistance training.
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