Stimulation of muscle protein synthesis by whey and caseinate ingestion after resistance exercise in elderly individuals
Journal Title (Medline/Pubmed accepted abbreviation):  Scand. J. Med. Sci. Sports
Year: 2011
Volume: 21
Page numbers: e372-e383
doi (if applicable): 10.1111/j.1600-0838.2011.01318.x

Summary of background and research design:
Background: Sarcopenia is the loss of muscle mass over time and it is a common problem in older individuals. It has been found that resistance training and ingestion of amino acids can prevent sarcopenia, but the details regarding type and timing of protein/amino acid supplementation have not been established.

Hypothesis: 1) Whey protein would lead to a faster rate of muscle protein synthesis compared to casein.
2) Protein consumed before or after the workout would lead to the same rate of muscle protein synthesis.

Subjects: healthy, moderately active elderly volunteers, age 68 ± 1 (n = 24; 15 men and 9 women)

Experimental design: randomized, parallel groups

Treatments: Protein beverages included 0.45 g protein/kg lean body mass and included L-[1-13C] leucine (in order to trace the fate of the protein)
1) Casein 30 min before exercise
2) Casein immediately after exercise
3) Whey immediately after exercise
4) Non-caloric control beverage

Protocol: At least 2 wks before the trial, 1 repetition maxima (1 RM) were determined for knee-extensions for the exercising leg (randomly selected) and leg press (bilateral). Also before the trial, a DEXA scan was performed to assess fat-free mass. A 3-day food and activity record was completed for the 3 days before the trial. On the day of the trial, subjects arrived fasted and catheters were inserted into both arms. One IV delivered a primed, continuous infusion of L-[1-13C] leucine; the other was for blood sampling. The participants performed 5 sets of 8 reps at 80% their previously determined 1 RM in both unilateral knee extension and bilateral leg press. At 30 and 390 min post-exercise, muscle biopsies were acquired from the "exercising leg". In addition, 11 blood samples were acquired during this recovery period. Fractional synthesis rate was calculated.

Summary of research findings:
  • There was no significant difference between groups before the trial.
  • Insulin concentrations peaked in the post-exercise period when protein was consumed post-workout. When casein was consumed pre-workout, insulin was higher immediately after workout than at baseline, but decreased steadily back to baseline. In the control group, insulin did not change. Total insulin response (area under the curve of insulin concentration vs. time for 15-390 min post-workout) was greater when protein was consumed post-workout.
  • Total amino acid concentration in blood was elevated in all protein-consuming groups, regardless of timing. Leucine concentrations were 2 times higher with whey at the peak compared to casein. Total leucine response (AUC) was greatest with whey. The AUC of casein post-workout was greater than the AUC of casein pre-workout. Similar trends were observed for plasma levels of essential amino acids.
  • 13C-ketoisocaproic acid (KIC) was higher in the groups that ingested protein post-workout, indicating more amino acid metabolism.
  • The workout lead to a greater myofibrillar fractional synthesis rate (FSR, or rate of muscle synthesis). Both post-workout protein supplements tended towards greater FSR, but the difference was not statistically greater than the control. There were no statistical differences between treatments.

Key practice applications:

Consumption of whey or casein led to similar rates of muscle synthesis regardless of whether the protein was ingested before or after the workout. A key factor to note is that protein synthesis rates were only measured at 30 and 390 min postexercise and there were no measures of overall protein balance. Thus, it is not known how the ingestion of whey and casein post exercise would have influenced protein synthesis at 3 h postexercise or if the treatments caused equivalent levels of overall protein balance in the muscles. Older individuals ought to engage in resistance training to prevent sarcopenia and consume high protein foods/beverages around the workout to maximize their gains, as convenient. Milk, specifically, which has a protein component of 80% casein and 20% whey, is recommended based on the findings from this study.
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