From Ergo Log
Using the amino acid leucine as a supplement also boosts the muscle building effect of slow proteins such as casein, according to a human study published by researchers at the University of Maastricht, Netherlands, in Clinical Nutrition. This means that leucine probably also enhances the anabolic effect of an ordinary well-balanced meal.
Leucine is an extremely interesting amino acid for athletes. About 3 g of the stuff will increase the impact of the proteins in your diet on your muscles. Muscle cells 'see' leucine and, depending on the amount of leucine they 'see', they decide how hard their anabolic machinery needs to work. It's hardly surprising that masses of natural bodybuilders swear by leucine, and add it regularly to their protein shakes.
Some sports nutritionists have wondered whether leucine boosts the anabolic stimulus of all sorts of protein. For one thing, amino acids enter the blood quickly. Even if you take them in combination with proteins that are digested slowly, the concentration of amino acids in the blood increases within an hour.
This is not the case for amino acids that you ingest in the form of protein. If you consume 'fast' whey protein, the amino acids in the whey make their way relatively quickly to your blood stream – not as fast as consuming separate amino acids, but faster than many other protein types, such as casein. Soya protein is a bit slower than whey, but faster than casein. The protein in beef, boiled and fried eggs is slower than casein.
So does leucine work when combined with a slow protein? Can muscle cells do anything with the anabolic stimulus from leucine if the amino acids in a slow protein still haven't managed to find their way to the muscle tissue?
The Dutch researchers answered this question in their study. They gave 12 men, average age 74, a shake containing 20 g casein [PRO], and 12 other men a shake containing 20 g casein and 2.5 g leucine [PRO+LEU].
The amino acid phenylalanine in the casein was labelled so that the researchers could see whether it was absorbed by the muscle tissue. The researchers took cells samples out of the men's leg muscles just before intake, after 2 hours and after 6 hours, and measured the amount of labelled amino acid from the casein had been absorbed by the muscle cells. Supplementation with leucine had increased the amino acid uptake.
The insulin level of the men who had the shake containing casein increased a little. The insulin level rose more when leucine was added. This partly explains the muscle enhancing effect of the leucine-casein combination, the researchers think.
They are searching for a dietary strategy that can help maintain muscle mass and strength in the elderly and protect against sarcopaenia. They believe they have found this.
"Fortifying meals with free leucine may represent an effective strategy to improve post-prandial muscle protein accretion", the researchers write. "This will be of particular interest in more compromised patient groups in whom total dietary protein intake is restricted."
Clin Nutr. 2013 Jun;32(3):412-9.