Protein supplementation augments the adaptive response of skeletal muscle to resistance-type exercise training: a meta-analysis.

Journal Title (Medline/Pubmed accepted abbreviation): Am. J. Clin. Nutr.
Year: 2012
Volume: 96
Page numbers: 1454-1464.
doi (if applicable):10.3945/ajcn.112.037556

Summary of background and research design:
Background: Consumption of protein after a workout is widely believed to aid in muscle protein synthesis and augment gains in muscle size and strength from resistance training.  However, some studies report that protein supplementation does not improve strength gains, especially in older participants who are susceptible to losses in muscle mass, strength, and functional capacity.

Hypothesis: Protein supplementation enhances gains in muscle mass and strength in combination with a resistance exercise routine.

Experimental Design: meta-analysis

Subjects: Data were collected from 22 randomized, clinical trials that included a total of 680 adult participants with a BMI less than 30 kg/m2.

Studies were included if they had at least one treatment group consuming >1.2 g/kg body weight/day and one placebo (low protein) group in conjunction with a resistance exercise routine that was at least 2 training sessions per week for at least 6 weeks.  These studies subsequently assessed changes related to fat free mass, fat mass, muscle fiber cross section area (size), and/or one repetition maxima.  Pre-supplementation and post-supplementation were collected to assess the differences due to the intervention.  The data were pooled to assess the overall size of the effect of protein (“effect size”).  Sensitivity analyses were performed to see if age (< or > 50 years old) or type of protein affected the effect size.
Summary of research findings:
  • Protein supplementation potentiated gains in fat free mass from a resistance exercise program (p < 0.00001).  The effect was observed in younger subjects (p < 0.00001) and older subjects (p < 0.00001) as well as younger trained and untrained subjects (both p < 0.001).
  • Loss in fat mass was not affected by protein supplementation (p > 0.05).
  • In conjunction with resistance training, protein supplementation augmented gains in muscle size, as assessed by both type I and type II muscle fiber cross sectional area (both p < 0.01).  However, a gain in cross sectional area of type II fibers was seen only in younger subjects (p < 0.00001 for younger subjects and p = 0.35 in older subjects).
  • Protein supplementation amplified the gain in muscle strength from the resistance training, as assessed by one repetition maxima for leg press (p < 0.001).  This result held true for both younger and older subjects (both p < 0.05).
  • Both milk-based proteins and supplements from a single protein source were effective at contributing to gains in fat free mass.
Key practice applications: Based on results from 22 different studies, protein supplementation aided in the gain of fat free mass in participants engaged in a resistance exercise program.&nbps; Protein supplementation also augmented gains in muscle mass and muscle strength.  These effects were true for adults of all ages and all types of protein assessed.  Consuming a protein supplement after a workout can increase gains in muscle strength and muscle size.
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