Many bodybuilders eat huge amounts of protein. In fact, several pro bodybuilders claim to take in more than 600 grams daily. Statements like that make many dietitians cringe. They believe that having too much protein leads to kidney damage, and the excess converts into bodyfat. In truth, however, even megadoses of protein don’t harm healthy kidneys, and protein is never converted into bodyfat in active people.
The more likely fate of excess protein in bodybuilders is oxidation in the liver. It’s simply burned up as an energy source. Because most bodybuilders prefer to have their protein used for muscle-building purposes, the question is what amount of protein maximizes muscle protein synthesis while preventing oxidation.
That question is particularly relevant in light of recent studies demonstrating that the only amino acids that play any significant role in muscle protein synthesis are the essential ones, which must be supplied by food. Just six grams of essential amino acids, or about the amount of protein found in a single egg, can trigger muscle protein synthesis following resistance exercise.
A study presented at the Experimental Biology 2007 meeting by a group of Canadian physiologists explored the protein requirement following a weight-training session. Specifically, the researchers sought to determine the cut-off level for protein synthesis after exercise before dietary protein was shunted into oxidation.
Six healthy men reported to a laboratory on five separate occasions to engage in an intense leg-training routine. After the workout they got a drink containing 0, 5, 10, 20 or 40 grams of whole-egg protein. They also received a four-hour infusion of the BCAA leucine, which was radioactively labeled to measure muscle protein synthesis. Increasing protein intake decreased leucine breakdown, as expected—the equivalent of an anticatabolic effect in muscle. Protein was shunted into oxidation in the subjects who had the 20- and 40-gram drinks. The authors conclude that any more than 20 grams of protein taken in would probably be oxidized.
Another study compared the effects of whey and casein on muscle protein synthesis after weight training. Whey and casein are the two major milk proteins, and previous research has shown that their metabolic properties differ. Whey protein is rapidly absorbed and digested, peaking about 90 minutes following intake. Since a rapid absorption of amino acids after exercise favors increased muscle protein synthesis, whey is often recommended as the ideal postworkout protein.
Casein curdles in the stomach. That, plus the presence of certain digestion-slowing peptides, leads to its slower rate of digestion. In fact, amino acids from casein can be released over a seven-hour span. Since the presence of amino acids in the blood exerts an anticatabolic effect in muscle, casein is often considered the ideal anticatabolic protein, particularly when taken shortly before sleep.
In the new study, eight healthy resistance-trained men engaged in a unilateral (one-leg-at-a-time) resistance workout on three occasions, after which they drank postworkout formulas that contained 10 grams of essential amino acids derived from whey protein, a whey-and-casein combo or casein alone. The pattern of amino acid entry into the blood wasn’t affected by the source of protein. The rate of protein synthesis was greater in the exercised than in the nonexercised legs (no surprise there!). There were, however, no differences in the rate of muscle protein synthesis between the three protein sources. The proteins apparently all enter the muscle at the same rate. IM