What Is Casein, and Does It Aid Muscle Growth?

If you want to up your protein consumption, protein powders provide a handy and relatively affordable option.

However, with seemingly endless varieties available, choosing the one that aligns with your health and fitness aims can be confusing.

One widely chosen option for muscle building is a milk-derived protein known as casein.

This piece covers everything you should know about casein, including its mechanism, advantages, and suggested dosages.

What is casein?

Casein makes up roughly 80% of the protein in cow’s milk, while whey constitutes the remaining 20%. Whey is the liquid fraction of milk, whereas casein is found in the curds.

Consider cottage cheese as an example — the liquid on top contains whey that has separated from the solid casein curds beneath. Fresh or unmixed yogurt often shows a similar separation where the whey-containing liquid pools apart from the thicker yogurt.

Casein protein is produced from skim milk. First, the whey is removed. The leftover milk curds are then rinsed, drained, dried, and milled into a powder.

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

Summary

Casein is the main protein in milk and can be isolated to create casein protein supplements.

How your body digests it

Both whey and casein are high-quality, complete proteins, meaning they provide all nine essential amino acids. Amino acids are the components of protein that the body needs to obtain from food when labeled essential.

Despite these similarities, your body digests and absorbs casein much more slowly than whey.

Older studies indicate this happens because the acidic environment in the stomach makes casein clot or form a gel. Consequently, it takes nearly twice as long for the body to digest and absorb an equal amount of casein compared with whey.

For this reason, whey is typically described as a fast-digesting protein, whereas casein is considered a slow-digesting protein.

Summary

Casein forms a gel in the stomach, substantially slowing how quickly it’s digested and absorbed.

Benefits

The slow-digesting nature of casein and its nutrient profile provide several advantages.

Muscle growth

Casein is a solid option if your aim is to increase muscle mass.

Although it digests and absorbs more slowly, research shows it can deliver muscle-building effects similar to whey when taken around workouts.

Furthermore, for promoting muscle growth during sleep, casein may be the superior nighttime option.

The gel formed by casein in the stomach supplies a steady flow of amino acids to muscles overnight, supporting recovery and growth.

Reduced hunger

Dairy proteins, particularly casein, help reduce appetite by boosting satiety and prolonging time between meals.

This effect stems from the several-hours-long digestion and absorption process.

Thus, adding casein to your diet can be useful if you’re aiming for weight loss or have trouble staying satisfied between eating occasions.

Rich in useful nutrients

Certain casein powders are excellent sources of calcium, offering around 50% of the daily value per serving.

Calcium is important for many bodily roles tied to bone, muscle, and cardiovascular health.

Additionally, casein contains bioactive peptides that have been found to lower blood pressure similarly to some commonly prescribed antihypertensive drugs.

Summary

Beyond supporting muscle growth, casein promotes fullness and provides beneficial nutrients like calcium and bioactive peptides.

Downsides

When deciding if casein is right for you, it’s important to weigh its perks against potential drawbacks.

A common allergen

Cow’s milk allergy is frequent in children, though most grow out of it, making it less prevalent in adults.

As the major protein in dairy, casein is a typical allergen. If you have a milk allergy, you should avoid foods and supplements containing milk proteins, such as casein and whey powders.

Avoid casein supplements if you’re allergic to soy as well, since many casein products include soy additives.

On the bright side, if you’re lactose intolerant, casein powders are generally safe because most or all lactose is removed during processing (14).

Less leucine than whey

Leucine is one of the three branched-chain amino acids (BCAAs); the others are isoleucine and valine.

While all amino acids contribute to muscle building, leucine is especially important for initiating the muscle synthesis process.

Whey typically contains about 26% more leucine than casein, which may make it more effective at stimulating muscle growth both at rest and post-exercise.

The quicker digestion and absorption of whey might also explain why it’s often considered better for muscle building than casein.

However, it’s not fully determined whether the greater acute stimulation of muscle growth seen with whey translates into larger long-term gains in muscle size and strength compared with casein.

Regardless, while leucine content and digestion rate are important for stimulating muscle growth, other aspects like total daily protein intake and distribution across meals likely matter more.

Summary

Casein is a common allergen and should be avoided if you’re allergic to milk. It also contains less leucine — the key BCAA that activates muscle-building — than whey.

Dosage recommendations

To maximize training results, it’s advisable to take 1–2 scoops (20–40 grams) of a high-quality protein like casein before or after workouts.

Still, while consuming protein around exercise can be beneficial, evidence indicates total daily protein intake is a stronger predictor of muscle size and strength. So if you meet an optimal daily protein target, exact timing is less critical.

The Recommended Daily Allowance (RDA) for protein is 0.36 grams per pound (0.8 grams per kg) of body weight. This amount prevents deficiency but isn’t necessarily optimal for body composition or performance.

If you train regularly, you may need two to three times the RDA — roughly 0.72–1.08 grams per pound (1.6–2.4 grams per kg) — to best support muscle growth and recovery. For someone weighing 150 pounds (68 kg), that equates to about 109–164 grams of protein per day.

You can help meet daily protein targets by consuming 1–2 scoops (20–40 grams) of casein before bed to limit muscle protein breakdown during sleep.

When mixed, casein can be thick, so use at least 8 ounces (237 mL) of water and blend or shake until smooth. Mixing with milk is an option for added protein and taste.

Alongside supplements, you’ll optimize muscle building by getting sufficient calories and protein from nutrient-rich whole foods like nuts, lean meats, fish, vegetables, whole grains, and fruit.

Summary

Casein can be consumed around workouts and before sleep to aid muscle recovery and growth.

The bottom line

Casein is a high-quality, slowly digested protein that helps support muscle recovery and growth.

It’s also high in calcium and contains bioactive peptides that may help lower blood pressure, and it promotes longer-lasting fullness.

While it’s generally safe for those who are lactose intolerant, people with a milk allergy should avoid it.