What Is Casein, and Does It Aid Muscle Growth?

Casein comprises around 80% of the total protein in cow’s milk, while whey accounts for the remaining 20%. Whey is the liquid part of milk, while casein is the curds (1).

Take cottage cheese, for example — the liquid settled on top contains whey that has separated from the firm casein-containing curds below. Newly opened or unmixed yogurt is another example of when you can often see the whey-containing liquid separated from the solid yogurt.

Casein protein is made from skim milk. First, the whey is drained away. Then, the remaining milk curds are washed with water, drained, dried, and ground into a powder.

Micellar casein is the most common casein protein supplement available and contains 80–82% protein by weight.

Summary

Casein is the predominant protein in milk that can be isolated to make casein protein supplements.

Both whey and casein protein are high quality, complete proteins, meaning that they contain all nine essential amino acids. Amino acids are the building blocks of protein, and you need to get the ones categorized as essential through your diet.

Despite their similarities, your body digests and absorbs casein at a much slower rate than whey.

According to older research, this is because the acidic environment in your stomach causes casein to clot or form a gel. As such, it takes your body nearly twice as long to digest and absorb the same amount of casein as it does whey (2, 3).

For this reason, whey protein is commonly characterized as a quickly digested protein, while casein is characterized as a slowly digested protein.

Summary

Casein protein forms a gel in your stomach, significantly slowing the rate at which it’s digested and absorbed.

The slow-digesting properties of casein protein and its nutrients offer several benefits.

Muscle growth

Casein protein is an excellent choice if your goal is to build muscle.

Despite its slower rate of digestion and absorption, it has been shown to offer muscle-building effects similar to those of whey protein when consumed around a workout (4).

Plus, when it comes to building muscle while you sleep, casein may be the better nighttime snack (5).

The gel that casein forms in your stomach supplies a steady stream of amino acids to your muscles throughout the night and supports muscle recovery and growth (5).

Decreased hunger

Dairy proteins, especially casein, reduce appetite by increasing feelings of fullness and delaying hunger.

This is because it takes several hours for your body to digest and absorb it.

As such, adding casein protein to your diet can be helpful if you have a weight loss goal or struggle to stay full between meals (6, 7).

High in beneficial nutrients

Some casein protein powders are an excellent source of calcium, supplying about 50% of the daily value per serving (8).

Calcium supports many bodily functions related to bone, muscle, and vascular health (9).

What’s more, casein protein contains bioactive peptides that have been shown to lower blood pressure in the same way as certain medications commonly prescribed to lower blood pressure (10, 11, 12).

Summary

In addition to aiding muscle growth, casein protein promotes feelings of fullness and contains beneficial nutrients like calcium and bioactive peptides.

When considering whether casein protein is right for you, it’s best to weigh its benefits with its potential downsides.

A common allergen

Cow’s milk allergy is common in children. Fortunately, most children outgrow it, making it less common among adults (13).

Being the major protein found in dairy, casein is a common allergen. If you have a milk allergy, you should avoid all foods and supplements that contain milk proteins, including casein and whey protein powder.

You should also avoid casein protein powder if you have an allergy to soy, as many casein products contain soy as an additive.

Fortunately, if you’re lactose intolerant, you can safely consume casein protein powder since most — if not all — of the lactose is removed during the manufacturing process (14).

Less leucine than whey

Leucine is one of the three types of branched-chain amino acids (BCAAs). The other two are called isoleucine and valine.

While all amino acids are important for building muscle, leucine is the one that triggers the muscle-building process (15, 16).

Because whey protein contains about 26% more leucine than casein, it may be more effective at stimulating muscle growth — both at rest and after a workout (17, 18, 19, 20).

The faster digestion and absorption of whey protein may also explain why it’s speculated to be better for building muscle than casein (21).

However, whether the greater stimulation in muscle growth provided by whey protein is significant enough to result in greater gains in muscle size and strength over time compared with casein protein isn’t fully established.

In either case, while the leucine content and rate of protein digestion and absorption are important determinants of muscle growth stimulation, other factors like total protein intake and protein distribution are likely more important (22, 23).

Summary

Casein protein is a common allergen and should be avoided if you have a milk allergy. Casein also contains less of the branched-chain amino acid called leucine, which helps kick-start the muscle-building process.

To reap the best results from your training, it’s best to consume 1–2 scoops (20–40 grams) of high quality protein like casein before or after your workouts (24).

Still, while it can be advantageous to consume protein around your workout, research suggests that your total daily protein intake is a better predictor of muscle strength and size. Therefore, as long as you get an optimal amount of protein each day, the timing becomes less important (25).

The Recommended Daily Allowance (RDA) for protein is 0.36 grams per pound (0.8 grams per kg) of body weight. This is the estimated amount needed to prevent a deficiency — not what’s optimal for body composition or health (26).

If you exercise regularly, you may need twice or even triple the RDA, or 0.72–1.08 grams per pound (1.6–2.4 grams per kg), to optimally support muscle growth and recovery. For a person weighing 150 pounds (68 kg), this equals 109–164 grams of protein per day (27, 28, 29).

You can meet part of your daily protein targets by consuming 1–2 scoops (20–40 grams) of casein protein before bed to reduce muscle protein breakdown while you sleep (27).

When mixed, casein protein powder can be thick, so make sure to use at least 8 ounces (237 mL) of water and blend or shake it until smooth. You can also mix the powder with milk for extra protein and flavor if preferred.

In addition to protein supplements, you can optimize muscle building by getting enough calories and protein from nutrient-dense whole foods like nuts, lean meat, fish, vegetables, whole grains, and fruit (28).

Summary

You can drink casein protein around your workouts and before bed to support muscle recovery and growth.

Casein protein is a high quality, slowly digested protein that supports muscle recovery and growth.

It’s also rich in calcium and bioactive peptides that may lower blood pressure and can help keep you feeling fuller for longer.

While it’s safe if you’re lactose intolerant, you should avoid it if you have a milk allergy.