Saturday, March 24, 2012

Can Too Much Protein Smother Muscle Gains? by Jerry Brainum

     Myostatin is a protein that prevents gains in muscle size and strength. Animals born deficient in the enzymes that produce myostatin show remarkable muscular size and less bodyfat. It doesn’t take a scientist to realize that depressing myostatin production is a good thing for bodybuilding purposes.
    A high-protein diet is considered necessary for building muscle and strength. Among its other effects is that certain amino acids (the elemental ingredients in protein) directly turn on genes that dictate muscle protein synthesis. Most notable are the essential amino acids, especially branched-chain amino acids.
      And yet, a recent study suggests that if you eat too much protein, you’ll defeat the entire purpose of bodybuilding.1 The researchers who conducted the study say that negative effects of a high-protein diet are caused by an increase in myostatin that results from higher protein intake.
The study featured rats, which were placed into one of three groups:
  1. 15 percent protein
  2. 25 percent protein
  3. 35 percent protein
      The protein was casein, a high-quality milk protein, and each group also got fat and carbohydrate. After three weeks the rats in the 35 percent protein group had the highest levels of myostatin synthesis. The 15 percent protein group had the lowest levels, while those in the 25 percent group showed a moderate myostatin increase. Based on that, the authors suggest that for building muscle, you shouldn’t take in more than 15 to 25 percent of your daily calories as protein.
     Before condemning a protein intake of 35 percent or greater as having negative effects on muscle growth, though, you need to consider a few issues. For one thing, the study used rats as experimental subjects, and the same results may not be applicable to humans, although some human studies have indeed shown no additional stimulation of muscular growth if the diet exceeds 15 percent protein.
     Nor did the rats in the study exercise, and past studies have shown an interaction between exercise—particularly weight training—and myostatin release. Most studies show that lifting weights blunts myostatin synthesis. In fact, a human study reported at the Experimental Biology 2006 meeting showed results that contradict the rat study.2
      Subjects in a control group got 15 percent of total calories as protein, and a high-protein group had a diet that was 29 percent protein. Both groups also engaged in weight training. After 24 hours of recovery from the exercise both groups had a 50 percent reduction in myostatin synthesis rates. By the 48-hour mark those in the high-protein group showed lower levels of myostatin than the control group. So the authors suggest that a high-protein diet extends the myostatin-blunting activity of weight training, thus promoting more muscular growth.
      Eating a higher-protein diet without lifting weights may increase myostatin release, but adding a weight workout blunts it.
1 Nakazato, K., et al. (2006). Increased myostatin synthesis in rat gastrocnemius muscles under high protein diet. Int J Sports Nutr Exer Metab. 16:153-165.
2 Pilegaard, H., et al. (2006). Resistance exercise and protein intake downregulate myostatin mRNA in human skeletal muscle. Paper presented at the Experimental Biology 2006 meeting of the Federation of American Societies for Experimental Biology, in San Francisco, California.


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