Protein shakes: Do they actually work?

Researchers Paul T Reidy and Blake B Rasmussen published an extensive 2016 review in the Journal of Nutrition on the scientific data regarding supplemental protein and amino acids for resistance training. The major summary points are followed by some overall conclusions drawn from the paper. 

 

Effect of Resistance training on muscle protein synthesis:

  • acute resistance exercise increases muscle protein synthesis stimulation by 0.07 - 0.12% / h but maximal levels are maintained for only 1 - 3 hours and then decline
     
  • 0 - 1 hour post-resistance training, the metabolic milieu changes from catabolic to anabolic.
     
  • after training, both muscle protein synthesis and protein breakdown increase and the result is a less negative protein balance, but in fed-state, the net protein balance is positive.
     
  • resistance training increases muscle protein synthesis by 65% and 40% for mixed and myofibrillar muscle protein synthesis, respectively.
     
  • If sluggish, the muscle protein synthesis peaks 2-3 hours post exercise (~60-70%) then declines at 4 hours after resistance exercise. It may decline during sleep but rebound in the morning.
     
  • resistance training in a fed state will increase muscle protein synthesis by 138%, 54%, 100% and 78% for myofibrillar, sarcoplasmic, mitochondrial and mixed components, respectively.
     
  • gender differences in post-resistance training protein metabolism do not seem to exist. The signalling of mTORC1a and protein synthesis don't seem to differ between men and women.

 

Effect of Protein and amino acid supplements on muscle protein synthesis:

  • 20g of Proteins/amino acids every 3 hours is more effective vs 40g/6 hours or 10g /1.5 hours in increasing myofibrillar muscle protein synthesis in fasted state. But exercise in the fasted state is not a common practice.
     
  • resistance exercise sensitizes muscle to amino acids for up to 24 hours post exercise and there is no difference between 1 to 3 hours post exercise. No optimal timing exists to maximize the effect of protein / amino acid supplementation.
     
  • optimal timing and dosing of protein supplementation around typical meal patterns is unknown
     
  • 20 - 30 g (~8-15g essential amino acids) likely to maximize post-exercise muscle protein synthesis in young men
     
  • soy, casein, whey, egg, and beef sources all increase post exercise protein synthesis
     
  • rapidly absorbed protein / amino acids increase maximal muscle protein synthesis quickly. Slowly digested proteins / amino acids result in a prolonged, delayed response in short acute studies
     
  • Whey has a higher branch-chained amino acid content and so is often seen as a superior source vs other isolated proteins but in studies examining >4 hours post-exercise protein synthesis, there is no difference in how the protein source effects the magnitude or duration of the muscle protein response
     
  • if the protein / amino acid dose contains sufficient leucine, the source does not seem to matter as long as the source is of high-quality, quantity, digestible and and contains all essential amino acids
     
  • adding 120 kcal of carbohydrates does not further stimulate muscle protein anabolism when sufficient essential amino acids are provided
     
  • a protein source containing ~1.8 - 2 g leucine would be sufficient to activate a post-exercise "leucine trigger" to increase protein synthesis.

 

Effect of protein / amino acid supplements on strength and performance outcomes:

  • There is a lack of clarity whether chronic protein supplementation during resistance training further enhances strength outcomes
     
  • Evaluating supplemented young adults 12, 24 and 36 weeks of a periodized resistance training program revealed: plateau at 12 weeks in lean mass gain with no extra benefit from supplementation.
     
  • About 90% of muscle hypertrophy occurs in the first 2 months of resistance training with no extra benefit from supplementation
     
  • Another meta-analysis revealed modest effect of protein supplements on muscle hypertrophy but no effect on strength. When considering total protein intake, the effect of protein supplements was negated all together. Total protein intake was the best predictor of improvements in muscle mass.
     
  • Little evidence exists for the "anabolic window." Only a handful of studies support protein timing whereas a host of both acute and chronic investigations indicate timing is inconsequential since exercise sensitizes the muscle to protein/amino acids up to 24 hours post-exercise.
     
  • when protein intake needs are met, any further changes in protein intake have less bearing on adaptations.
     
  • distribution, amount and spread of protein throughout the day may have greater relevance
     
  • current protein intake recommendations for strength athletes are: 1.2 - 1.8g / kg of body weight / day.
     
  • no particular protein source type or form provides a greater enhancement of strength over another high quality source when looking at various studies.
     
  • individual variability exists in response to protein / amino acid supplementation



Current research limitations:

  • It could be possible that current studies are too short to fully elucidate the effects of supplements
     
  • studies may lack number of subjectsnumbers and thus may suffer from lack of statistical power
     
  • methodologies such as proper assessments of lean body mass and the location of protein distribution may not be optimal

 

Researchers' concluding statements:

"It is clear that for most RET (resistance exercise training) outcomes, the protein / AA effect after resistance training is moderate to low at best... Only a small effect of protein/AAs on whole-body lean body mass was evident in some studies, but minimal to no effect on strength or muscle mass was consistent."
 

"Muscle becomes more sensitive to AA availability for at least 24 h after a bout of exercise. Therefore, participants who consume sufficient daily energy and protein in a balanced diet are not likely to enhance muscle growth and strength with protein/AA supplementation during RET, although slight increases in whole body lean mass are possible but may not be clinically relevant. .. However, for those who consume a poor diet, with limited energy or protein, the total amount, quality, and distribution pattern of protein intake throughout the day may be useful in enhancing muscle growth and possibly function, if impaired, in response to RET."



Reference
P Reidy & B Rasmussen. Role of ingested amino acids and protein in the promotion of resistance exercise-induced muscle protein anabolism. The Journal of Nutrition. 2016 Feb;146(2):155-83


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George Cho