There is a very good scientific review in the Journal of the International Society of Sports Nutrition with some really good info on Protein that I will summarize. For those of us who've heard it before it will be a nice reminder and for the newbies it will be a big help. The most important thing I wanted to really highlight is the importance of the BCAA Leucine.
The purpose of this review was to determine whether past research provides conclusive evidence about the effects of type and timing of ingesting specific protein sources by those engaged in resistance weight training. The review targets the effects of intake and timing of the following protein sources on physical outcomes: whey, casein, milk, soy and essential amino acids.
Protein timing and the effects on muscle hypertrophy and strength in individuals engaged in weight training
Researchers have tested the effects of timing of protein supplement ingestion on various physical changes in weightlifters. In general, protein supplementation pre- and post-workout increases physical performance, training session recovery, lean body mass, muscle hypertrophy, and strength. Specific gains, differ however based on protein type and amounts. The leucine content of a protein source has an impact on protein synthesis, and affects muscle hypertrophy. Consumption of 3–4 g of leucine is needed to promote maximum protein synthesis. An ideal supplement following resistance exercise should contain whey protein that provides
at least 3 g of leucine per serving. A combination of a fast-acting carbohydrate source such as maltodextrin or glucose should be consumed with the protein source, as
leucine cannot modulate protein synthesis as effectively without the presence of insulin. Such a supplement post-workout would be most effective in increasing muscle protein synthesis, resulting in greater muscle hypertrophy and strength. In contrast,
the consumption of essential amino acids and dextrose appears to be most effective at evoking protein synthesis prior to rather than following resistance exercise.
Leucine and muscle protein synthesis
The leucine content of a protein source has a major impact on protein synthesis, and affects muscle hypertrophy.
Leucine has been indicated as the sole stimulator of protein synthesis, and leucine alone appears to be nearly as effective in stimulating protein synthesis as when all branched chain amino acids (BCAAs) are consumed. Leucine also seems to have both insulin-dependent and insulin-independent mechanisms for promoting protein synthesis. Approximately 3 to 4 g of leucine per serving is needed to promote maximal protein synthesis.
A clinical study
(Koopman et al Am J Physiol Endocrinol Metab 2005) compared the protein synthesis response to a post workout drink containing either carbohydrates, carbohydrates and protein, or carbohydrates + protein + leucine. The results showed a huge improvement in whole body protein balance during recovery from resistance exercise compared with the ingestion of carbohydrate or carbohydrate with protein.
Protein supplement intake studies: a comparison of timing protocols
Cribb et al. assigned 23 male bodybuilders
to one of two groups: those who received a supplement a) before and after a workout, or b) in the morning and evening. The supplement contained 40 g protein (from whey isolate), 43 g carbohydrate (glucose), and seven g creatine monohydrate per 100 g. All participants followed a preliminary resistance weight-training program for 8–12 weeks before baseline measurements were taken.
Results indicated significant differences in body composition in the group consuming the supplement pre- and post-workout. This group experienced increased LBM and decreased body fat. Both groups demonstrated increases in strength, but the pre- and post-workout group demonstrated significantly greater gains, indicating that timing of the ingestion of the protein supplement was crucial.
Hartman et al.
conducted a study
comparing the post workout use of 500ml fat free milk, soy protein drinks with the same macronutrient ratio as milk, or carbohydrate drinks by 56 young untrained males. Muscle fiber growth was significantly higher in the milk drinking group than the soy and control groups, as was the gain in total fat free mass. This shows that Soy is a less effective form of protein than milk protein (whey & casein) despite it having a slightly higher BV than casein.
Types of protein
Besides looking at leucine content protein, quality can be compared on two scales most relevant to this review: biological value and protein digestibility corrected amino acid score. Biological value (BV), determines how efficiently exogenous protein leads to protein synthesis in body tissues once absorbed and has a maximum score of 100, using egg protein as a value of 100, which is why it is possible to go over 100. PDCAAS numerically ranks protein sources based on the completeness of their essential amino acid content, and has a maximum score of 1.0.
Three sources of dairy protein typically used in studies of muscle hypertrophy and strength are cows milk, casein and whey. Cows milk is a highly bioavailable source of protein, comprising 80% casein and 20% whey . Overall, cows milk has a BV of 91 and a PDCAAS of 1.00 indicating that it is readily absorbed by the body, promoting protein synthesis and tissue repair, and provides all essential amino acids (EAAs). Casein, with a BV of 77 and a PDCAAS of 1.00 exists in micelle form, and within the stomach will gel or clot, thus resulting in a sustained release of amino acids. Compared with milk, it is less bioavailable, but like milk, it provides all EAAs. Whey, the other protein found in milk, with a BV of 104 and a PDCAAS of 1.00 is superior to both milk and casein. It contains all EAAs, and its excellent bioavailability leads to rapid protein synthesis.
Soy is a vegetable-based protein source that is useful for vegetarians and individuals who are lactose- or casein-intolerant. Soy has a BV of 74 and PDCAAS of 1.00, indicating that it is not as bioavailable as milk based protein, but does contain all EAAs. The BV and PDCAAS of other protein sources can be viewed below:
Reference: Journal of the International Society of Sports Nutrition 20129:54
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