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Soya protein and casein equally good for muscles

When it comes to muscle growth it makes no difference whether you get your proteins from soya or from dairy products. Researchers from the University of Maastricht and the University of Arkansas discovered this from a human study they did.

The researchers gave 22 subjects a mixture of proteins and maltodextrin for 4 hours, fed via a tube through the nose. Half of the subjects were given a fluid containing soya protein [SOPM], the other half got casein [CAPM]. The amounts of soya protein and casein were balanced so that both groups received the same amount of nitrogen. Over the entire period of the experiment the subjects received about 16-20 g protein.

At the same time the researchers gave the subjects labelled amino acids and took small samples of muscle tissue from their leg muscles, so they could measure the build-up and breakdown of muscle tissue. They found no significant differences, but overall the soya protein produced the biggest build-up [muscle PS] and the biggest breakdown of muscle protein [muscle PB].

Soya protein and casein equally good for muscles

Soya protein and casein equally good for muscles

When the researchers calculated the net result, the fractional rate of mixed muscle protein synthesis was a tiny bit higher in the soya group, but again not significantly.

Soya protein and casein equally good for muscles

At the level of individual amino acids, soya protein and casein have different effects on muscle cells, the researchers discovered. But in terms of the net effect, there is no difference between the two proteins. To paraphrase Mao Tse Tung: it doesn't matter if it's a white cat or a black cat, as long as it catches mice.

Soya industry representatives have reacted positively to the study on supplements websites. "This study shows that both soy and casein decrease muscle protein breakdown, which is important for maintaining muscle", states Marc Cope of Solae, a giant soya manufacturer. Cope wonders what the results would have been like if the subjects had also done exercise. "Previous studies have shown soy is superior to casein for muscle protein synthesis in exercising individuals", says Cope. [ 16-Aug-2010]

The researchers have other ideas. Milk protein contains relatively high amounts of leucine, which is not found in soya protein. Leucine is an interesting amino acid. It enhances anabolic mechanisms in muscle cells. To do this you need at least 3-5 g leucine, according to studies, and in practice natural bodybuilders use doses of 7-10 g. The amount of protein the subjects received was nowhere near enough to set the leucine effect of casein in motion, the researchers suspect.

On the other hand though: soya protein is a much better source of arginine than dairy protein is. Perhaps the optimum pre work out protein shake should contain both soya and dairy proteins.

Clin Nutr. 2010 Aug 2. [Epub ahead of print].

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