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Proteins: Milk, Whey, Casein, Soy and more

It is important to have a fundamental understanding of what a protein is, to then understand their role. Read on to find out what a protein is actually made up of, and what the different types are.

Jeukendrup Sports Nutrition Sport Science

What is a protein?

Let’s start with exploring what a protein is. Proteins are made up of smaller building blocks called amino acids, joined together in chains. There are 20 different amino acids but there are endless ways to combine these building blocks into various proteins, with distinct shapes which serve various functions in our body. It is like having 20 different pieces of Lego that can be used to make all sorts of shapes. Some proteins are just a few amino acids long, while others are made up of several thousands. Some are quite simple structures, others are 3 dimensional and very complex.

What are proteins used for in the human body?

The human body has over 10,000 different proteins that are all important for normal functioning. Our body makes these proteins using DNA as the instruction manual. These instructions which are present in each cell in our body show the cell exactly how to put the amino acids together. It is comparable to the instructions that come with Lego. The amino acids are either made in the body or derived from foods. If they are derived from protein in foods, this protein will be broken down first into amino acids (a process called digestion) and will then be absorbed. Some amino acids (9 in total) cannot be made by the body and we have to rely on them to be delivered by foods. These are the essential or indispensable amino acids. Food proteins that contain most or all of the essential amino acids are called high quality proteins or complete proteins. Proteins that only have a few of the essential amino acids are lower quality proteins or incomplete proteins. Generally animal proteins (meat, milk, eggs) are higher quality proteins than plant based proteins. Now let's look at some of these proteins in a bit more detail.

Milk protein

Cow’s milk consists of water, protein, fat and some sugar and minerals. There are two types of protein in milk: casein and whey. When milk sours and starts to separate, a process called coagulation, it automatically divides out the proteins into semi-solid lumps and a liquid portion. Casein is found in the lumps, or curds, whereas the whey protein is found in the liquid portion. The curds, a bit like cottage cheese, is used to make cheeses, a process during which the liquid part (whey) is removed. The ratio of protein within a glass of milk is about 20% whey and 80% casein. Human milk contains more whey and less casein (about 40%:60%).

There are two types of protein in milk: casein and whey.

Whey is known as the “rapid” or “fast acting” protein, meaning that the body can break it down and absorb the nutrients quickly. Casein takes longer to digest and it releases amino acids into the bloodstream more slowly. It is therefore often referred to as the “slow” or “slow acting” protein. Additionally, whey is high in essential amino acids such as the branched-chain amino acids (BCAAs) that the body cannot produce on its own and must derive from food. Manufacturers can process whey protein further to make it more pure and eliminate ingredients that are not protein. These are then often sold as protein powders or used to manufacture other food products.

Whey is known as the “rapid” or “fast acting” protein

Whey protein typically comes in 4 major forms...

1. Whey protein concentrates

Concentrates have typically a lower (but still significant) level of fat, lower levels of sugar in the form of lactose and cholesterol. Depending on how concentrated the whey protein concentrate is, the percentage of protein can vary between 30% and 90%.

2. Isolates

Isolates are further processed to remove the fat, and lactose, but are usually lower in micronutrients as well. Isolates powders are typically 90% protein by weight. Like whey protein concentrates, whey protein isolates are mild to slightly milky in taste.

3. Hydrolysates

Hydrolysates are whey proteins that are pre-digested. This makes them even faster because now there is less time needed to digest the protein in the intestine and the amino acids are readily available for absorption. The cost of hydrolysates is generally higher and the taste can be pretty unpalatable.

4. Native whey protein

Native whey protein, is the most processed and purest form of whey protein and is very low in other nutrients. It is extracted from skim milk.

Other proteins

There are many other proteins like egg protein and meat protein (pork, beef, poultry, fish). As mentioned above these animal sources of protein are usually high in essential amino acids. Vegetarians rely on plant based proteins such as soy protein or proteins found in beans. Rice protein, potato protein, pea protein and many other sources have received some attention in the media as well recently. Of the plant based proteins soy is one of the most common proteins. It is a relatively high quality protein and can be found in many food products, including sports nutrition products.

Which type of protein is best?

Depending on the article you read and often depending on what type of protein a company wants to sell, attractive theories are developed around each of these proteins. There are claims that slow proteins are better than fast proteins and vice versa. In future articles we will discuss the evidence and what research has actually taught us about the role of these proteins for athletes.


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