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PROTEIN DIVERSIFICATION: YOUR KEY TO GROWTH!

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The_Bulldog:
PROTEIN DIVERSIFICATION: YOUR KEY TO GROWTH!
Digestion Rates Influence Skeletal Muscle Protein Synthesis



This brief will cover the first step in utilizing protein to build muscle – digestion and absorption – and how this step affects the rate that amino acids are incorporated into skeletal muscle.

Key Points:
    * Skeletal muscle mass increases only if the rate of skeletal muscle protein synthesis (SMPS) exceeds the rate of skeletal muscle protein breakdown (SMPB) over time.
    * Casein, whey protein, and isolated soy protein appear to have different digestion rates, with casein designated as “slow,” whey protein as “fast,” and soy protein as “intermediate.”
    * Protein digestion rate is an independent factor regulating skeletal muscle protein retention.


Skeletal Muscle Protein Synthesis
For adults who do not train, skeletal muscle mass is unchanged because the overall rate of skeletal muscle protein synthesis (SMPS; the rate at which amino acids are incorporated into skeletal muscle proteins) equals the rate of skeletal muscle protein breakdown (SMPB; the rate at which amino acids are released from skeletal muscles).  Skeletal muscle hypertrophy, or muscle growth, occurs only during anabolic periods when SMPS exceeds SMPB [1].   Conversely, skeletal muscle atrophy, or muscle loss, occurs during catabolic periods when SMPB exceeds SMPS.

Skeletal muscle proteins are constantly being degraded and synthesized, such that at any given time, the difference between the two processes determines whether you are in an anabolic or catabolic state.  A weight lifting session causes SMPS to exceed SMPB [2,3].  As long as three hours after weight lifting, SMPS rates are more than two to four-fold greater than SMPB [2,3], such that over a 24-hr period, SMPS slightly exceeds SMPB [1].  Thus weight training combined with proper nutrition eventually leads to visible muscle gains as this effect is repeated day after day.

Delivering amino acids to muscles as soon as possible following your workout is essential for adding muscle mass.  We all know by the “pump” we feel after a great set that blood flow increases to skeletal muscle while we lift.  Well, during the first several hours after training, blood flow to your muscle remains elevated [2,4].  Consuming protein during this time is critical because the increased blood flow more efficiently delivers absorbed amino acids to your muscles [2,4].   The increased amino acids availability coupled with your just completed workout, stimulates SMPS more than just the exercise or amino acids alone [4,5,6,7].  We refer to this critical three hour period following your workout as an “anabolic window” – a critical time for you to reap the benefits of your hard work!   Research shows that the combination of weight training with a protein feeding within the “anabolic window” improves muscle mass gains compared to delaying the same feeding [8,9].  Of more concern, the failure to feed your exercised muscles during recovery can actually lead to muscle protein loss [3]!


Digestion Rates
Amino acid levels in blood following consumption of casein, whey protein, and ISP (isolated soy protein) have been reported [10-13], though not directly compared.  Although casein, whey protein, and ISP are about 97% digested [14], their rates of digestion differ [10-13].   The latter finding is important because protein digestion rate directly influences muscle protein retention [15].

After consuming whey protein, blood amino acid levels rise abruptly (reaching their maximum a little after an hour) then return to pre-feeding levels within about three hours [10,11].  After soy protein is ingested, there is a relative delay in blood amino acid appearance with values peaking between two and three hours and returning to baseline within four hours [12].   Casein is a different animal because it “clots” in the stomach [16], which significantly delays its absorption [10].  Although blood amino acid levels are highest about an hour after consuming casein the blood amino acid concentration is only about half that observed after the same amount of protein from whey is ingested; however, blood amino acid levels change little from this “peak” over the next six to seven hours [10,13].  These findings have led researchers to classify whey protein as a “fast” protein and casein as a “slow” protein [10].  Because ISP tends to fall in between the two dairy proteins, it is now being referred to as an “intermediate” protein.



It may seem logical that the faster a protein is digested the sooner muscles will start to grow because amino acids will be delivered more quickly to muscles.  Hold on though.  Unfortunately, our body does not like to be flooded with amino acids.  When this happens after ingesting a “fast” protein, amino acid oxidation or breakdown occurs, which diminishes the amount of amino acids that can be delivered to wanting muscles [10,15].  This can actually cause muscle protein balance to be less over a 7 to 8 hour recovery period than when a “slow” protein is consumed [10,15].  Soy protein is digested at a rate faster than milk protein, which is 80% casein and 20% whey protein [12], but the abrupt rise in blood amino acids associated with whey protein ingestion is lessened [11,12].  Even so, soy protein ingestion increases amino acid oxidation compared to milk because milk’s high casein content significantly slows the digestion rate [12].  However, when we look at what is going on in muscle, we see that differences in protein digestion rates significantly influence SMPS.  Soy protein and whey protein, when consumed right after exercise show a similar ability to stimulate SMPS after an hour [17] whereas casein ingestion does not increase SMPS [15].  Although amino acid oxidation is increased after consuming both ISP and whey protein, significant amounts of amino acids are still delivered to muscles, including the key amino acid leucine [10,15] that stimulates protein synthesis [18,19].  Even though delivery of amino acids to skeletal muscle is prolonged after casein consumption, levels within the muscle are likely insufficient to stimulate protein synthesis [15].  Herein lays the rationale for blending proteins in the bars and beverages you consume.  Whey protein quickly stimulates SMPS [10,15] and opens the “anabolic window;” soy protein likely extends the time that the “anabolic window” is maximally open; and, casein prolongs delivery of amino acids to muscles to keep the “window” from closing [10,15].

Research indicates that ingesting both “fast” and “slow” proteins is likely to be more effective for stimulating SMPS than a single protein source [20].  The combination of 80% casein and 20% whey as skim milk powder consumed immediately after exercise appears to stimulate SMPS more over the first three hours of recovery than soy protein [20].  It should be noted that only at three hours after exercise was SMPS different between groups.  Since others have shown that post-exercise consumption of soy protein and whey protein similarly stimulate SMPS one hour after exercise [17], it looks like the differentiating factor in skim milk is the slowly absorbed casein, not the whey.  In another study, participants consuming 40 grams of whey protein and 8 g of casein daily as part of a 10-week weight training program saw greater lean body mass gains than those who consumed 40 grams of whey protein and 8 grams of amino acid [21].  As amino acids are even more rapidly absorbed than whey protein [15], this study suggests that the “fast” and “slow” protein blend is better for building muscle than solely consuming “fast” proteins (i.e., the whey protein/amino acid blend).

To summarize, whey protein, soy protein, and casein are designated “fast”, “slow”, and “intermediate” proteins based on their respective digestion rates.  Ingesting the combination of a “fast” protein to turn on SMPS and a “slow” protein to prolong amino acid delivery to tissues appears to be a better muscle-building strategy than ingesting either a single protein source or a single protein type (i.e., a “fast” protein) based on SMPS responses.  It seems reasonable to assume that adding an “intermediate” protein like ISP to a whey protein and casein blend might further improve muscle growth by maximizing the “anabolic window” as described earlier, but more research is needed.

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REFERENCES

1.    Phillips SM:  Protein requirements and supplementation in strength sports.  Nutr 20:689-695, 2004.

2.    Biolo G, Maggi SP, Williams BD, Tipton KD, Wolfe RR:  Increased rates of muscle protein turnover and amino acid transport after resistance exercise in humans.  Am J Physiol 268(3 Pt 1):E514-E520, 1995.

3.    Phillips SM, Tipton KD, Aarsland A, Wolf SE, Wolfe RR:  Mixed muscle protein synthesis and breakdown after resistance exercise in humans.  Am J Physiol 273:E99-E107, 1997.

4.    Biolo G, Tipton KD, Klein S, Wolfe RR:  An abundant supply of amino acids enhances the metabolic effect of exercise on muscle protein.  Am J Physiol 273(1 Pt 1):E122-129, 1997.

5.    Dreyer HC, Drummond MJ, Pennings B, Fujita S, Glynn EL, Chinkes DL, Dhanani S, Volpi E, Rasmussen BB: Leucine-enriched essential amino acid and carbohydrate ingestion following resistance exercise enhances mTOR signaling and protein synthesis in human muscle.  Am J  Physiol Endocrinol Metab 294(2):E392-400, 2008.

6.    Tipton KD, Elliott TA, Cree MG, Wolf SE, Sanford AP, Wolfe RR:  Ingestion of casein and whey proteins result in muscle anabolism after resistance exercise.  Med Sci Sports Exerc 36(12):2073-2081, 2004.

7.    Børsheim E, Tipton KD, Wolf SE, Wolfe RR:  Essential amino acids and muscle protein recovery from resistance exercise.  Am J Physiol Endocrinol Metab 283(4):E648-57, 2002.

8.    Esmarck B, Andersen JL, Olsen S, Richter EA, Mizuno M, Kjaer M:  Timing of postexercise protein intake is important for muscle hypertrophy with resistance training in elderly humans.  J Physiol 535(Pt 1):301-311, 2001.

9.    Cribb PJ, Hayes A:  Effects of supplement timing and resistance exercise on skeletal muscle hypertrophy.  Med Sci Sports Exerc. 38(11):1918-25, 2006.

10.    Boirie Y, Dangin M, Gachon P, Vasson MP, Maubois JL, Beaufrère B:  Slow and fast dietary proteins differently modulate postprandial protein accretion.  Proc Natl Acad Sci USA 94(26):14930-14935, 1997.

11.    Farnfield MM, Trenerry C, Carey KA, Cameron-Smith D:  Plasma amino acid response after ingestion of different whey protein fractions.  Int J Food Sci Nutr 8:1-11, 2008.

12.    Bos C, Metges CC, Gaudichon C, Petzke KJ, Pueyo ME, Morens C, Everwand J, Benamouzig R, Tomé D:  Postprandial kinetics of dietary amino acids are the main determinant of their metabolism after soy or milk protein ingestion in humans.  J Nutr 133(5):1308-1315, 2003.

13.    Lacroix M, Bos C, Léonil J, Airinei G, Luengo C, Daré S, Benamouzig R, Fouillet H, Fauquant J, Tomé D, Gaudichon C: Compared with casein or total milk protein, digestion of milk soluble proteins is too rapid to sustain the anabolic postprandial amino acid requirement.  Am J Clin Nutr 84(5):1070-1079, 2006.

14.    Protein quality evaluation in human diets.  Report of a Joint FAO/WHO Expert Consultation.  Rome, Food and Agriculture Organization of the United Nations, 1991 (FAO Food and Nutrition Paper No. 51).

15.    Dangin M, Boirie Y, Garcia-Rodenas C, Gachon P, Fauquant J, Callier P, Ballèvre O, Beaufrère B:  The digestion rate of protein is an independent regulating factor of postprandial protein retention.  Am J Physiol Endocrinol Metab 280(2):E340-348, 2001.

16.    Mahé S, Roos N, Benamouzig R, Davin L, Luengo C, Gagnon L, Gaussergès N, Rautureau J, Tomé D:  Gastrojejunal kinetics and the digestion of [15N]beta-lactoglobulin and casein in humans: the influence of the nature and quantity of the protein.  Am J Clin Nutr 63:546-52, 1996.

17.    Anthony TG, McDaniel BJ, Knoll P, Bunpo P, Paul GL, McNurlan MA:  Feeding meals containing soy or whey protein after exercise stimulates protein synthesis and translation initiation in the skeletal muscle of male rats.  J Nutr 137(2):357-362, 2007.

18.    Anthony JC, Anthony TG, Layman DK:  Leucine supplementation enhances skeletal muscle recovery in rats following exercise. J Nutr 129(6):1102-1106, 1999.

19.    Anthony JC, Anthony TG, Kimball SR, Jefferson LS:  Signaling pathways involved in translational control of protein synthesis in skeletal muscle by leucine.  J Nutr 131(3):856S-860S, 2001.

20.    Wilkinson SB, Tarnopolsky MA, Macdonald MJ, Macdonald JR, Armstrong D, Phillips SM:  Consumption of fluid skim milk promotes greater muscle protein accretion after resistance exercise than does consumption of an isonitrogenous and isoenergetic soy-protein beverage.  Am J Clin Nutr 85(4):1031-1040, 2007.

21.    Kerksick CM, Rasmussen CJ, Lancaster SL, Magu B, Smith P, Melton C, Greenwood M, Almada AL, Earnest CP, Kreider RB:  The effects of protein and amino acid supplementation on performance and training adaptations during ten weeks of resistance training.  J Strength Cond Res 20(3):643-653, 2006.

sasacg:
Brate,toliko si dobrih tekstova postavio,i nastavljas i dalje...

Svaka cast :wink:

The_Bulldog:
Eh, sad je lakse...kad imam podrsku takvih kolega...neko na eng., neko na srp..neko zalegne u nekoj drugoj prici... :-)

nenadns:
odlican text!!!! Bulldog for president! :D

The_Bulldog:
he-he-he...ma, ovo je cisto uzivanje ;-)

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