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Casein vs. Whey: Which Protein Should You Choose?

As one of the most popular dietary supplements in the world, millions of people rely on protein powder to meet their daily protein needs.  In addition to aiding in the body’s production of things like enzymes and hormones, protein also plays an important structural role in muscle tissues (along with all of the other tissues in the human body).(1)

While there are all kinds of different protein powders currently on the market., casein, and particularly whey, are by far the most popular.  In addition to being best-sellers, both types of protein have also been well-researched, with literally hundreds of different studies published to date.  

But what exactly is the difference between casein and whey protein and is one kind really better than the other?  To answer these questions, we’re going over everything that sets each type of protein apart.  Before we get too far ahead of ourselves though, let’s first talk a little more about why people take protein supplements in the first place.  

Benefits of Protein Powder Supplements

All of the muscles throughout your body are made up of proteins, which naturally go through a state of turnover -- through things like physical activity, some of these proteins become degraded and must be replaced. In fact, somewhere around 1% of all your muscle proteins are turned over each day.   

It’s through your diet that your body gets the proteins -- and ultimately the amino acids -- it needs to repair and replace damaged muscle tissues -- this general process is known as muscle protein synthesis (MPS).    

In the long run, in order to maintain your muscle mass, you need to have a protein balance, which means that the amount of protein coming in through your diet is equal to the amount that your body breaks down over the course of a day.  

The problem is, maintaining a protein balance is even harder if you’re an athlete or someone who regularly works out.  Research suggests that high-intensity training can drastically increase the number of proteins your body breaks down, requiring an increased daily protein intake just to maintain what muscle you already have.(2)

If your body doesn’t have a sufficient supply of dietary protein both before and after you exercise, it results in a negative protein balance, where more muscle proteins are being broken down than replaced.  In addition to impinging on your ability to recover post-workout, a negative protein balance can also lead to muscle wasting over time.  

That’s why protein powder supplements like casein and whey are especially popular amongst athletes and fitness enthusiasts -- because getting an adequate supply of the protein your body needs to rebuild and recover can be difficult to do through diet alone if you lead a relatively active lifestyle.  

What is Casein Protein?

Casein is the predominant protein found in cow’s milk, generally making up around 80 percent of its total protein composition.  It’s also the main reason behind milk’s white appearance.  

As far as protein powders go, casein comes in two basic forms. It most often comes in its natural micelle form, which is basically an aggregate of molecules dispersed within another substance.  This allows casein to clot together in the stomach during digestion, giving it a unique quality as a protein.(3)

But casein can also come in hydrolysate form, where the proteins go through additional purification processes such as heat treatment and/or adding in proteolytic enzymes in attempts to improve the digestive properties.  

What is Whey Protein?

Like casein, whey is also a bovine-derived protein, making up the other 20% of proteins found in cow’s milk.  Whey is a translucent liquid byproduct of the cheese manufacturing process -- whey is ultimately what remains after coagulation and the removal of curds.     

In order to create whey protein powder, proteins are separated from the remaining translucent liquid and purified to varying degrees -- different purification techniques ultimately produce different concentrations when all is said and done.  Whey protein concentrates can be anywhere from 30% to 80% pure protein, while whey protein isolates are generally over 90% pure.  

Casein vs Whey: What’s the Difference?

Photo by Kelly Sikkema

While casein and whey may both be derived from cow’s milk, that’s just about where the similarities between the two end.  Each type of protein is ultimately defined by a unique set of characteristics that affects how they interact with your body.  

From containing different concentrations of amino acids to having different absorption times, there are several factors that set casein and whey apart from one another.(4)

Casein and Whey Have Different Digestion Rates

One of the biggest differences between casein and whey has to do with the rate at which your body digests them. Whey protein is water-soluble and is quickly broken down and absorbed into the bloodstream.(5)  In other words, it’s a fast-digesting protein, with large quantities of amino acids becoming available quickly after consumption.(6)

Researchers have demonstrated that whey protein produces a quick spike in the concentration of amino acids in the bloodstream, with levels returning to baseline within 3 hours -- whey protein isolate is broken down and absorbed in as little as 1 hour after consumption, while whey concentrate usually takes a little longer to digest.(7)

Conversely, casein is known as a slow-digesting protein because it takes a relatively long time to be fully broken down and absorbed into the bloodstream.  As a water-insoluble substance, casein ultimately coagulates in the gut, resulting in a much slower rate of digestion.(8)

Instead of becoming rapidly available in large quantities like with whey, amino acids gradually enter the bloodstream over a longer period of time with casein protein.  

Following consumption, studies show that a sustained increase in the concentration of amino acids in the bloodstream usually lasts for around 7 hours before returning back to baseline; however, the immediate spike in plasma amino acids is much less substantial in comparison to whey protein.(9) Take a look at this graph for more detail:

They Have Different Amino Acids Profiles

Another thing that sets casein and whey apart from one another is their amino acid profile.  Amino acids are the building blocks of muscle tissue and ultimately what proteins are comprised of.  There are 9 amino acids that are referred to as essential because your body cannot produce them on its own.  

Instead, these essential amino acids (EAAs) must be obtained from dietary protein sources.  A protein that contains all 9 EAAs is known as a complete protein.  Complete proteins are the best kind of proteins because they provide your body with all of the nutrients it needs to repair and maintain its tissues -- the absence of any essential amino acid can ultimately impinge on your body’s ability to maintain its normal processes.(10)

While both casein and whey are complete proteins, they have different amino acid profiles, meaning that although they contain all 9 EAAs, their concentrations of each particular amino acid differs.  On top of that, they also contain different amounts of other non-essential amino acids as well.  

For example, whey protein contains high concentrations of leucine, isoleucine, and valine --  3 essential amino acids known as Branched Chain Amino Acids (BCAAs) along with an ample supply of the non-essential amino acid cysteine.(11)

Casein, on the other hand, contains fewer BCAAs but has higher concentrations of histidine, phenylalanine, and methionine -- all essential amino acids.

Casein and Whey have Different Biological Values

On top of having different amino acid profiles, casein and whey also have different biological values (BV).  BV is a standardized measurement of protein quality that looks at how much of the protein actually gets used in the formation of new tissue after all is said and done. 

A high biological value -- close to or even eclipsing 100 -- ultimately reflects that the protein contains a high supply of all 9 essential amino acids, while a lower BV suggests that the protein may be high in some back lacking in others.(12)

To date, whey protein has the highest biological value of any protein that’s currently been measured, ranging from 104 for concentrates all the way up to 140+ for some isolates.  Casein, on the other hand, has a more modest biological value of 77, which is less impressive than whey but still higher than many other types of protein.  

Protein Source Bioavailability Index
Whey Protein Isolate* 100-159
Whey Concentrate* 104
Whole Egg 100
Cow's Milk 91
Egg White 88
Fish 83
Beef 80
Chicken 79
Casein* 77
Soy 59

Casein vs Whey: Which Protein Should You Choose?

According to numerous studies and several different standardized assessments of protein quality, whey protein appears to be the better overall protein.  With a higher biological value, more robust amino acid profile, and quicker digestion time, whey protein may be better than casein when it comes to both building muscle and losing weight.  

But that doesn’t mean casein is ineffective -- you can still pack on plenty of muscle mass or shed body fat with casein -- whey is just simply more effective.  Though, one thing that casein may actually be better suited for is overnight recovery. 

Whey is Better for Building Muscle

Numerous studies have demonstrated that compared to casein, muscle protein synthesis (MPS) is induced to a greater degree both at rest and after exercise with whey.(13) Again, MPS refers to the actual process through which your body builds muscle tissue -- the higher your levels of MPS are, the greater your muscle-building potential will be.  

For example, a 2012 study published in the British Journal of Nutrition recruited healthy older men to compare the effects of micellar casein and whey protein isolate on MPS.(14)

The researchers gave participants either a whey or casein protein supplement following a session of resistance training -- in the training session, subjects only worked out one leg.  Following the workout, the researchers monitored subjects’ MPS responses in both their trained and untrained legs. 

They ultimately found that on average, exercise-induced levels of MPS in the trained leg were significantly higher in the whey group in comparison to the casein group.  On top of that, the researchers also observed that in the untrained leg, MPS was an average of 65% higher in those who consumed whey protein compared to those who were given casein.  

Research suggests that these findings can largely be attributed to two things: whey’s fast absorption properties and its superior amino acid profile -- especially it’s high leucine content.(15)(16) All in all, these factors help to make whey protein the best type of protein powder currently on the market when it comes to building muscle.  

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Whey May Better for Weight Loss

While whey itself doesn’t necessarily induce weight loss -- it takes a hypocaloric diet to lose weight -- it has been found to enhance weight loss outcomes to a greater degree than casein.  For example, one study found that compared to casein, those who took a whey protein supplement expressed greater feelings of satiety following consumption, leading to a reduction in food cravings.(17)

Another 2011 study ultimately found that regular consumption of whey leads to greater decreases in body fat in comparison to casein.  The researchers also found that those who consumed whey were also less susceptible to subsequent weight regain.(18)

On top of that, whey may also be better than casein when it comes to reducing some of the risk factors associated with metabolic syndrome.  For instance, a 2010 study published in the British Journal of Nutrition ultimately found that compared to participants who took casein, those who were given whey protein demonstrated significant decreases in total and LDL cholesterol as well as fasting lipid and insulin levels following 12 weeks of consumption.(19)

Casein is Ideal For Overnight Recovery

While whey may be the better protein when it comes to building muscle and losing weight, casein’s slow rate of digestion makes it better suited when it comes to overnight recovery post-exercise.   

Sleep is the primary time in which your body makes repairs -- including rebuilding damaged muscle proteins.  Because digestion can take up to 7 hours with casein, it’s the perfect protein to take before you go to sleep and your body enters into a fasted state.    

Research has shown that individuals who consumed a casein protein supplement prior to going to bed were ultimately able to sustain increased plasma amino acid levels throughout the entirety of the night.(20)

Furthermore, those who took casein before bed, on average, saw a greater net protein balance and higher levels of MPS over the course of their sleep, leading to a reduction in things like Exercise-Induced Muscle Damage and Delayed Onset Muscle soreness (DOMS).

Wrap Up

Whey and casein are two of the most popular types of protein powder currently on the market, however, there are several things that set them apart.  Each has a different rate of digestion, with whey being a fast-digesting protein, while casein takes much longer to be broken down and absorbed into the bloodstream. 

On top of that, they also have different biological values and amino acid profiles, with whey having a higher BV and a more well-balanced amino acid profile containing higher concentrations of leucine (along with other BCAAs).  

Because of these factors, whey is a better protein when it comes to both building muscle and losing weight.  However, casein’s slow-digestion rate makes it better suited than whey for overnight post-exercise recovery.  

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