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Leucine is not a panacea

Leucine is an interesting amino acid that boosts the anabolic effect of proteins. Nevertheless, a shake containing 25 g whey isolate still works better than a shake containing 6 g whey plus a spoonful of leucine powder, sports scientists at McMaster University in Canada discovered.

Leucine increases the anabolic impact of amino acids, and scores of studies have confirmed this. But just how effective is leucine really? Can you for example swallow a couple of capsules of leucine with a glass of milk instead of drinking a protein shake? This is the question the Canadians set out to answer in their study, which was published in June 2012 in the Journal of Physiology.

The researchers did a trial using 24 male students, average age of 22. The students first had to do four to-failure sets of 10-12 reps on the leg press, and another four similar sets on the leg extension machine. The students only did the exercises with one leg, and immediately afterwards they drank a shake.

One group of eight students were given a shake containing 25 g whey isolate [Whey]. The 25 g whey contained 3 g leucine.

A second group of eight students were given a shake containing 6.25 g whey isolate to which the researchers had added a couple of grams of leucine so that these students also consumed 3 g leucine [Leu].

A third group of eight students were given a shake containing 6.25 g whey isolate plus extra essential amino acids but not leucine [EAA-Leu]. The students were given all essential amino acids except leucine, and received the same amount as the students in the Whey group. The EAA-Leu shake contained only 0.75 g leucine.

The researchers then took biopsies over a period of five hours so that they could measure the synthesis of muscle proteins [FSR] in the students' legs. The figures below show that the three shakes all worked equally well in the non-trained leg [Fed], but that 3-5 hours after intake whey performed better in the trained leg [Fed-Ex].

Leucine is not a panacea

Leucine is not a panacea

The figures above show the effects that the shakes had on anabolic signal molecules such as mTOR and p70S6K. You can see that 25 g whey has more effect than the whey-amino acid mixes.

"Only whey, containing both essential amino acids and non-essential amino acids, was able to sustain the elevated rates of muscle protein synthesis 35 hours after resistance exercise and therefore may be a better choice to support resistance exercise induced anabolism", the researchers conclude.

J Physiol. 2012 Jun 1;590(Pt 11):2751-65.

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