These two terms are often used interchangeably, but they do not mean the same thing. The difference is simple: whey is a type of protein powder, not a synonym for it.
The relationship between the two
Protein powder is the collective term for all powders in which protein is concentrated. That includes animal sources such as whey, casein and egg, and plant sources such as pea, rice, hemp and soy.
Whey is one of them. It comes from milk and is a by-product of cheese making: the clear liquid left behind when milk curdles. That is filtered, concentrated and dried into powder.
So all whey is protein powder, but not all protein powder is whey.
Why whey stands out in this list
The difference between protein sources lies not only in the amount of protein, but above all in its composition. Proteins consist of amino acids, and nine of them your body cannot make itself. Those have to come from food.
Whey contains all nine, in a ratio that aligns well with what muscle tissue needs. What specifically sets it apart is its leucine content.
The role of leucine
Leucine is one of those nine essential amino acids, but it does more than simply supply building material. It acts as a signalling compound: it sets off the process of muscle protein synthesis, in which your body builds new muscle tissue.
That process has a threshold. Below roughly two to three grams of leucine per eating occasion it does not get going properly. Go above it and it is switched on.
Whey naturally contains enough leucine to reach that threshold with a normal serving of twenty-five to thirty grams. That makes it efficient: you need relatively little of it.
How plant proteins compare
Plant sources individually have a less complete amino acid profile. Pea protein, for instance, is rich in lysine but lower in methionine; with rice protein it is precisely the other way around. And the leucine content is generally lower than in whey, meaning you need a larger serving to reach that same threshold.
There is a solution for that: combining sources. Where one falls short, the other makes up for it. For that reason our Vegan Protein consists of three complementary sources, pea protein isolate, rice protein isolate and hemp protein, which together give the most complete amino acid profile possible.
What that means for your choice
If you eat dairy, whey is the most efficient option per gram. If you eat plant-based or tolerate dairy poorly, a well-composed plant powder works too, provided it combines several sources. A single plant protein is a less complete choice.
About the author
Kemail Verhoeven is the founder of AP Nutrition. He has played sport for fifty years across basketball, martial arts, strength training and triathlon, and after a series of injuries and broken bones he immersed himself in injury prevention, recovery, nutrition and movement science. That knowledge is self-taught and forms the basis of the products AP Nutrition develops and manufactures in-house.
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