Difference between Whey and Casein

Both whey and casein are milk proteins; they have a lot in common, but at the same time are completely different. Both of them exist as popular sport supplements consumed for accelerating the growth of muscle mass during weight training and can be just as well consumed as part of a balanced diet. Some athletes prefer to either stick to one of these supplements or to take both of them. The question is: are they complements or substitutes, or is one much more important than the other? You will find the answer to these questions in this article.


Whey Protein vs Casein
Whey protein

Whey protein is one of the major milk proteins. This protein type is highly appreciated among professional and amateur athletes due to its extended amino acid profile and immediate absorption. Whey protein breaks down into amino acids in the digestive tract almost fully and really quickly due to its quite simple molecular structure. Whey protein takes second place after egg albumen for its bioavailability and high concentration of BCAA (branch-chained amino acids). Therefore, whey protein is excellent for muscle growth and recovery when taken right after a workout or after waking up before breakfast.

In the range of sport supplements whey protein is available in 3 popular forms: isolate, concentrate and hydrolysate.

  • Whey protein concentrate is the least processed whey protein type among these three. Raw whey is dried, purified of fats and carbohydrates (as much as natural filtration can provide) and packed. Whey protein concentrate contains most of the natural vitamin and mineral content whey possesses and has most of its natural molecular structure.
  • Whey protein isolate is a concentrate that has been additionally processed. This processing is more thorough; it eliminates more carbohydrates and fats and makes the final product even more bioavailable and increases its absorption.
  • Whey protein hydrolysate is additionally processed isolate. It is rarely used in protein shakes because of its bitter taste, but is a quite popular ingredient for amino acid supplements as it contains them in a form that is almost “digested” for easier absorption.

All three types can be referred to as “whey protein”.

Casein protein

Casein protein is the most abundant milk protein, and is also known as “slow-digested” milk protein. It is relatively insoluble, but it interacts with water by forming special structures called “micelles” in order to be digested. That is the reason why casein doesn’t supply amino acids to the plasma immediately: the increase in blood amino acids and protein synthesis is observed in about 3-4 hours after consumption. In addition, casein is high in calcium and phosphorus – essential minerals for physical and mental activity.

This superior long-lasting effect of slow protein release provided by a serving of casein protein shake is attributed to the micellar gel-like structure casein obtains in the process of digestion. It remains in the stomach for a long period and has a slow absorption rate from the gastrointestinal tract to the blood.

Whey Protein vs Casein

What is the difference between whey protein and casein? There are quite a few of them. First of all, these two types of protein have different amino acid profiles and molecular structure. Whey protein mixed with water or milk makes a liquid light shake, while casein shake is much thicker and makes you feel fuller.

But the most important difference is their absorption speed. If comparing whey to casein protein by this parameter using a scale of 1-10 (where 10 is the fastest), whey would get a 10 and casein a 2.

Does that mean that whey protein is superior and more preferable if your goal is to protect and build muscles? No. Whey and casein are better together.

Immediate whey absorption results in a significant increase of amino acids in blood plasma. It is crucial after a workout, when the muscles lack amino acids for recovery and building new structures. The high amino acid content in plasma leads to more intense protein synthesis as the body’s own protein is not affected by that.

That is also the reason why whey is great for muscle protection against catabolism immediately after waking up in the morning. At least 8 hours without nutrition depletes the natural resources of free amino acids in the blood, which may lead to muscle breakdown performed by the organism to transfer amino acids to organs and other body systems. Whey protein shakes help prevent this process quickly and effectively.

This advantage of whey protein is at the same time its disadvantage: whey protein is superior at augmenting rapid protein synthesis, but due to its quick digestion and absorption this effect doesn’t last long. In less than one hour amino acid supply from a whey protein shake is depleted and the body requires new fuel sources.

To put it simply, the real muscle growth is the ratio between building up body protein from amino acids (anabolism) and breaking down body protein to amino acids (catabolism). The thing is not only to boost the anabolic mechanisms, but to slow down the catabolism manifestations.

An interesting study was carried out: researchers offered 30 g of protein to a group of healthy individuals. Half of them received whey and the others were given casein. For the following 7 hours test subjects underwent a number of tests that included anabolic and catabolic effect measures.

Whey protein intake led to a rapid increase of amino acid content in blood plasma and protein synthesis, but the effect was short-lived, i.e. whey consumption showed anabolic effect, but it was gone quickly.

Casein protein intake led to prolonged increase in blood amino acids and although it didn’t show much anabolic effect, it resulted in 34% reduction in protein breakdown, i.e. showed very good results in slowing down catabolism.

When the net protein balance over this 7-hour period was compared in two groups, those who took casein had a more positive balance than those who took whey.

Slow casein absorption is not necessarily a drawback of this protein type. On the contrary, it can turn out to be its main advantage. First of all, casein is able to slow down the rate of protein breakdown in the body. This is a clear advantage for long periods without food, such as night sleep. Taking casein before bedtime helps reduce body protein breakdown and protect your muscles by providing slow and gradual amino acid supply for about 8 hours.

The bottom-line is that since whey is perfect for protein synthesis increase and casein is essential for slowing down the protein breakdown, the combination of the two would be ideal.

Whey protein is most effective before and after a workout and first thing in the morning. Make sure you have a meal within 20-60 minutes after a whey protein shake as your body will need one already. It provides greater muscle anabolism.

A combination of whey and casein (20-25 g of protein per shake) can be taken an hour before a workout and right after it to maintain the amino acid supply.

Casein is ideal as an evening snack, because it will fuel your muscles with amino acids all night long. Also casein is a preferable option if you realize you probably won’t have a chance to have a meal for the next 3 hours or more.

Comparison Chart

Whey protein Casein protein
Quickly digested milk protein Slowly digested milk protein
Supports anabolism Fights against catabolism
Great to be consumed first thing in the morning and after a workout Ideal as a night-time protein and for long periods without regular meals


Here is an informative video in case you need more detailed information on the topic