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Optimal protein dose after weight training is twenty grams

If you take protein immediately after training to stimulate muscle tissue increase, the optimal dose is twenty grams. A higher intake only increases the breakdown of amino acids in the body, write sports scientists at McMaster University in Canada in a soon-to-be published article in the American Journal of Clinical Nutrition.

An increased concentration of amino acids in the body stimulates the growth of muscles, as does weight training. In the muscles these stimuli activate signalling proteins like mTOR, S6K1 and elF2B, and as a result the cells manufacture more muscle proteins.

Say then that after training you drink a protein shake – milk, quark, soya or chicken – to optimise your muscle growth, how much protein do you need? An obvious question, but not one that researchers have paid much attention to. Until now.

The Canadians got six students to train their leg muscles. They did four sets of eight to ten reps with the leg-press, leg-extension and leg-curl. The last sets they did to failure. Two days before the training the students got a standard diet with 1.4 g protein per kg bodyweight per day. Right after a training session the students got a protein shake. The amount of protein in the shake was ten, twenty, thirty or forty grams.

Four hours after the students had drunk the protein shake, the researchers measured the build up of muscle fibre and the amino acid metabolism. The graph below shows the effect of the shakes on the mixed-muscle fractional protein synthesis – the muscle build-up.

Optimal protein dose after weight training is twenty grams

The twenty-gram shake had the most effect. It increased the production of muscle fibre by 93 percent compared with a training session where no protein was consumed afterwards. A higher intake has hardly any extra effect.

The researchers also examined the manufacture of albumin in the liver. This protein is found in the blood and the body can use it as an extra source of amino acids if it needs to. The researchers had expected that an extra high protein intake might not stimulate extra manufacture of muscle protein, but that the protein might be stored in the form of albumin – as a buffer you could say. But this was not the case, as you can see from the graph below.

Optimal protein dose after weight training is twenty grams

Shakes containing more than twenty grams of protein do promote the burning of amino acids. The researchers discovered this by measuring the oxidation of the amino acid leucine in the blood of the test subjects.

Optimal protein dose after weight training is twenty grams

"The point at which amino acid oxidation significantly increases reflects the level at which protein intake becomes excessive", the researchers write. "Suggestive of a nutrient excess, leucine oxidation in the present study was stimulated after ingestion of 20 and 40 g of protein. In addition, muscle and plasma albumin protein synthesis were maximally stimulated at 20 g of dietary protein, which suggests an upper limit for incorporation of amino into these protein pools had been reached."

We have a different theory. The body needs time to digest proteins. The more protein you consume, the longer the digestion process takes. The body’s amino acid requirement in the muscles is greatest during and immediately after a training session. The higher doses that the Canadians used needed more time to be digested and were given too late. If the Canadians had given their test subjects the protein before the training session, then they would have probably discovered that higher doses of protein do provide an extra anabolic stimulus.

Am J Clin Nutr. 2008 Dec 3. [Epub ahead of print].