What is whey protein?

We hear so much about whey: “The ideal protein for recovery”, “the optimal protein for muscle building”, “the best protein for athletes”. But what is whey protein really? What makes whey so special? Whey is a byproduct of cheesemaking. If you have ever opened a container of yogurt and wondered what the liquid is on top: that is whey. Whey protein is a collection of proteins that we can find in whey. Whey protein is produced from milk. Cow milk contains about 80% casein and 20% whey.

How is whey protein made?

Cheesemaking starts with fresh milk. Step 1 is acidifying the milk. This can be done by adding an acid or by adding bacteria that turn the sugars in milk into lactic acid. The second step is to add a coagulant, often this is rennet. Now, the curds (casein) and whey (watery fraction) will start to separate.


The solid portion that can be separated from the curdled milk is called curd and whey protein is the water-soluble part of milk. If we remove the whey, the curd will form the cheese. The type of acidification used, the coagulant added, the way of separation curd and whey, the “cutting of whey and curd” and the duration of various steps are all important factors that will result in different types of cheese.

Now let's get back to the watery byproduct: whey. The protein fraction in whey constitutes approximately 10% of the total dry solids in whey. The remaining 90% are mainly sugars and fat. This protein is typically a mixture of beta-lactoglobulin (~65%), alpha-lactalbumin (~25%), bovine serum albumin (~8%), and immunoglobulins. This is not so important for the function because these proteins will be broken down when digested and the effect of whey on protein synthesis will come from the delivery of the amino acids in it.

Whey can be dried and is often sold as a powder that we find in the whey protein supplements we know. Most supplements have added flavouring and some of the supplements have added carbohydrates (for taste reasons or to help with glycogen restoration after exercise).

What is the best type of whey protein?

We can distinguish several different types of whey supplements. They vary mostly in the concentration of whey. Sometimes more than 80% of the protein is whey. In this case we call it a whey protein concentrate. The overall product will, however, not only contain whey protein but also lactose and fat. The whey protein can be further processed to remove carbohydrate and fat so we end up with a supplement that is 90% whey. We then call this a whey protein isolate. There is another product we often see on the market and this is a whey protein hydrolysate. Here the whey protein is pre-digested, meaning that enzymes are added to completely or partially break down the protein into the individual amino acids. The potential advantage of a hydrolysate is that it is even faster absorbed. However, there is little evidence for superior effects on protein synthesis. Generally, the more processed the whey protein is, the more expensive the end product. Typically you will find these types of whey protein as supplements:

  • Whey protein

  • Whey protein concentrate

  • Whey protein isolate

  • Whey protein hydrolysate


What makes whey special?

Whey is a high quality protein, which means that is has all of the amino acids, including all of the essential amino acids. Whey is also a protein that is well absorbed, making its delivery faster than many other proteins. So, the fact that it contains all the amino acids and can be delivered rapidly makes this one of the best proteins to consume post exercise.

The amino acid composition of whey protein is depicted in the infographic below and compared to casein and soy (Soy has been the most effective plant-based protein tested so far). The most important difference is the leucine and the total essential amino acid (EAA) content, which are very high in whey compared with other protein sources.