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Protein and Muscle Size Increase

New studies answer the question: Do you need more aminos to grow?

It may seem on par with those who insist that the earth is flat, but some self-styled nutrition experts insist that bodybuilders need no more protein than a couch potato does. Two recently published studies that examined protein use specifically for building muscle, however, show that protein type and timing are of fundamental importance.

The first study lasted 14 weeks and compared the results of taking protein or carbohydrate after training.1 The participants were 22 men, average age 23, none of whom had trained in the six months prior to the study. Nor had they used any food supplements that could be construed as having ‘anabolic’ properties, such as creatine or protein drinks.

The men were divided into two groups, with one group getting protein, the other carbohydrates. The protein serving contained 16.6 grams of whey, 2.8 grams of casein, 2.8 grams of egg white protein and 2.8 grams of L-glutamine. The carb serving contained 25 grams of maltodextrin. Both supplements contained an equal number of calories, and both were heavily flavored with vanilla to disguise which was which. The subjects took them before and after each workout and in the morning on rest days.

All the men trained only their legs during the study, using standard exercises, such as leg presses, leg extensions and leg curls.They did the workout three times a week for 14 weeks, doing three to four sets of each exercise.

The results were hardly surprising. Only those in the protein group showed gains in muscle size and strength. The training and additional protein led to an 18 percent size increase in the type 1, or slow-twitch, muscle fibers, and a respectable 26 percent increase in the size of type 2, or fast-twitch, muscle fibers. Despite using an identical training program, those who got only the carb supplement gained nothing.

Why would anyone compare protein with carbs as a way of encouraging muscle gains? Past studies show that taking in carbs after a workout appears to blunt the effects of cortisol, an adrenal catabolic hormone that increases with exercise. Blunting the effects of cortisol would tip the balance toward muscle growth, and carbs promote an insulin release that drives amino acids into muscle. Amino acids must be present as protein, however, for that to occur. As the study shows, carbs without protein do nothing to promote muscular gains.

The second study compared the effects of milk and soy proteins in promoting muscle growth in young men.2 Some authors have mistakenly identified soy as a slow-acting protein, but like whey it is, in fact, a rapidly absorbed protein source. That, however, is where the similarity ends. Whey supports muscle protein synthesis because of its rapid uptake, while soy protein more rapidly degrades in the liver and supports liver protein synthesis more than muscle.

The study mentions previous research (reported in this column) showing that when you increase whey protein intake, its efficiency drops, likely due to greater oxidation in the liver. The efficiency of soy, though, drops even more. So if you get amounts of protein that exceed the requirement for muscle protein synthesis, most of the excess will be oxidized in the liver.

Some scientists who study protein metabolism think that suddenly limiting protein in those who, like bodybuilders, have a habitually high protein intake can result in a negative nitrogen balance’again, because of upgraded liver oxidation of excess protein. The scientists think that the body gets so used to oxidizing protein that if you take in less, the body will increase the breakdown of existing protein’as in muscle. That’s a controversial theory that isn’t supported by a large body of proof.

The other fate of excess protein is conversion into fat, though that doesn’t happen in active people. That doesn’t keep ‘ex’perts’ from saying that ‘eating too much protein can make you fat.’ Well, yes, but only if you do nothing more physical than press buttons on your TV remote.

In the new study, intake of milk protein led to a markedly greater uptake of amino nitrogen than soy did. Another part of the study found that milk protein was far more efficient than soy in promoting muscle gains.

Clearly, there is no reason to add soy to a milk protein blend. Soy offers no advantages from an anabolic perspective, and it tends to promote internal organ protein synthesis instead of skeletal muscle. Soy does offer one advantage: It’s cheap and a good filler, so you can use less of the higher-grade milk proteins. IM


1 Andersen, L.L., et al. (2005). The effect of resistance training combined with timed ingestion of protein on muscle fiber size and muscle strength. Metabolism. 54:151-56.
2 Phillips, S., et al. (2005). Dietary protein to support anabolism with resistance exercise in young men. J Amer Coll Nutr. 24:134S-139S.

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