Does Whey Protein Also Contain Casein? We Sort Out The Milk Protein Mystery Once and For All.
Dear Fitness Nerd,
I’m a little confused about whey and casein protein. Does whey also contain casein? And vice versa? All I know is that both whey and casein are in milk. Can you help me sort this out? — Janine (Dunwoody, GA)
You’re right that both whey and casein are proteins in milk.
But the important thing to grasp is that they are two totally different kinds of protein.
So in their purest form – isolated from the milk itself (for example in protein powder supplements) — whey typically doesn’t contain meaningful amounts of casein. Same goes for casein in regards to whey content.
Understanding Milk Proteins: Whey vs. Casein
The easist way to think about this is in the context of milk.
Milk contains about 80 percent casein protein, and 20 percent whey. Under normal conditions, you would never be able to differentiate between the whey and casein in milk visually. It just looks … well … liquid and “milky.”
However, when you add an acid or enzyme like rennet (which is used in cheese production), the milk will curdle. This literally separates the whey from the casein proteins.
The result is that the whey — which is a semi-clear liquid — will rise to the top, while the casein (which is heavier and coagulates in the presence of an acid or enzyme) will usually sink to the bottom.
In cheesemaking, the whey is siphoned off from the casein, and the solids are then drained through a cheese cloth, further extracting any residual whey or water and leaving the firm casein solids, which are then shaped into blocks of cheese (there are more steps, but I won’t get into them here.)
Cottage Cheese: Whole Food Example of Casein and Whey
For a whole food, real world example, just think about cottage cheese (also known as “curds and whey,” for good reason.)
Cottage cheese is basically milk that has been separated into casein and whey via enzymes. The lumpy curds are the casein and the liquid part is the whey. So in this regard, when you eat cottage cheese you are getting both whey and casein protein.
Here’s the kicker: Outside of cottage cheese, for years whey was typically discarded or fed to livestock.
This practice persisted until scientists realized that the whey contained a very high level of fast digesting, bioavailable protein. Suddenly people started rushing to figure out ways to turn the liquid into a powder and the entire whey protein craze took off.
Difference in Whey Versus Casein
Whey and casein have very different chemical properties.
While whey digests quickly, casein can take hours to be broken down and absorbed. Casein is poorly dissolved in water and cannot be denatured (meaning it won’t change it’s natural structure with the application of heat or chemicals.)
This makes whey an ideal protein right after you workout, when you want to make sure plenty of protein is available to assist with recovery.
Casein, on the other hand, releases amino acids more slowly into your body, almost like a protein IV. This can help blunt muscle breakdown for hours after weight training. A combination of the two appears to be ideal, based on recent research.
Casein is also an ideal protein to consume in the evening or before you go to bed, since it may help reduce muscle breakdown during sleep. A serving of low-fat cottage cheese, skim milk, yogurt, Quark or kefir before bed is a low-fat, high-protein source of both casein protein and whey, although as I pointed out earlier, these products tend to have more casein than whey by volume.
When Doesn’t Whey Have Casein?
If you consume whole food sources of dairy, you’ll be consuming both whey and casein together. There is zero wrong with this.
However, if you take a 100% whey protein powder, there will be little to no casein present in the protein.
Same goes for a 100% casein protein powder, which will have isolated any residual whey out of the casein. The reason for this is that the filtration and isolation process more or less removes all traces of fat and the other protein. Casein molecules are “larger” and hence won’t make it through most whey filtration processes.
The exceptions in terms of protein supplements are things like milk protein isolate products, which may also contain some whey, as well as protein powder blends that intentionally contain both casein and whey protein.
Also protein powders that are labeled ”Whey Protein Concentrate” may also have trace amounts of casein, since the filtration process used to make concentrate products doesn’t capture all of the casein.
However, if you are consuming either whey isolates or casein isolates, there will be very little cross-over between the two.
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