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.

What are the benefits of whey protein?

Studies that measure the rate of protein synthesis after exercise have observed whey to be more effective than other protein sources such as casein or soy. It is therefore not surprising that whey is often used to promote muscle gain and limit muscle loss during periods of low energy intake. Of course, protein with a similar composition will also have similar effects but when the effects of a fixed amount of protein are compared whey seems to slightly outperform other proteins.

Protein synthesis post exercise was highest with whey followed by soy and casein. This is likely the results of amino acid composition and speed of absorption.

Should all athletes take whey supplements?

I think the answer to the question "should all athletes take whey protein supplements" is no. Although studies show benefits of whey in a head to head competition with some other protein sources. And if 100 grams of whey is compared to 100 grams of another protein it may give slightly better results. The same effects might be achieved by consuming a little more of another protein or by combining larger amounts of other proteins. We discussed some of this in the review of the movie game changers and in this guest blog on animal versus plant proteins by Oliver Witard: you can get the same effects by combining different proteins. Besides this, it is far more nutritious to eat foods that are naturally high in protein whether this is poultry, meat or fish or plant-based protein sources such as beans, chick peas, and nuts or plant based protein supplements (oat, wheat, soy, corn, pea , potato, rice). But, if you had to pick one convenient protein source and you want to take in a certain amount of protein, a protein shake or supplement may be very convenient and if you could only take a fixed amount, whey would probably be the most effective.


  1. Gorissen SHM, Crombag JJR, Senden JMG, Waterval WAH, Bierau J, Verdijk LB, van Loon LJC. Protein content and amino acid composition of commercially available plant-based protein isolates. Amino Acids. 50(12):1685-1695, 2018.

  2. Tang JE, Moore DR, Kujbida GW, Tarnopolsky MA, Phillips SM. Ingestion of whey hydrolysate, casein, or soy protein isolate: effects on mixed muscle protein synthesis at rest and following resistance exercise in young men. J Appl Physiol (1985). 107(3):987-92, 2009.


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