How much protein do you really need?

Many studies support the use of whey protein for building muscle mass. Early work focused on whey’s rapid digestion and ability to elevate amino acids in the blood quickly after ingestion. Now researchers are digging deeper into the qualities of whey to determine why. They’re realizing the higher amount of leucine in whey protein may be the key to its muscle building effect.

For example, the average amount of leucine in 25 grams of protein from whey, casein, and soy is 3.0, 2.3, and 1.5 grams, respectively. For reference, milk contains two proteins (20% is whey and 80% is casein).

Leucine is a special amino acid that does more than provide one of the building blocks for proteins. Leucine also triggers muscle cells to start making protein. Researchers have discovered that the concentration of leucine in the blood is the primary driver of muscle protein synthesis. This “leucine threshold” hypothesis explains why whey is so effective. The minimum threshold range is thought to be about 1.7 to 2.4 grams of leucine for resistance-trained young men, while inactive or older individuals need more. 

All else being equal, to elevate leucine levels and thereby increase muscle protein synthesis to the same extent as 25 grams of protein from whey, you would need to consume about 33 grams of protein from casein or 50 grams of protein from soy.

However, leucine’s muscle-building effect is only optimized when taken with the other essential amino acids. Therefore, taking leucine all by itself will not have the same effect as taking it with a complete protein (one that has all the essential amino acids).

Although casein protein is lower in leucine, it has the advantage of being a slower-digesting protein that helps protect against muscle breakdown. For this reason, some people combine whey with a milk-based (casein) protein to get the muscle-building benefits of whey with the anti-catabolic effects of a slower-digesting protein like casein or milk protein isolate or concentrate. If you favor plant proteins, then take 50 grams of protein to maximize muscle protein synthesis or take 25 grams and add 1.5 grams of leucine to boost its leucine levels to that of whey.


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