What Is Casein?

Casein is a milk protein used as a dietary supplement

Casein is the chief protein found in dairy products. While you may recognize casein from the supplement aisle, the role of casein in modern society extends beyond its common use as a protein powder. In addition to bodybuilders, casein has contributed to the lives of cheese-lovers, infants, and even clothing manufacturers.

Here's an overview of casein, including the potential risks and benefits of adding it to your meal plan.

Chocolate-flavored protein powder with casein
 Gabriel Vergani / EyeEm / Getty Images

What Is Casein?

Casein is a complete protein, meaning it contains all of the essential amino acids required by our bodies to function. In its purest form, casein is a white-colored solid with no taste. All mammals produce casein as a component in milk for their offspring.

Human breast milk consists of 40% casein and 60% whey, while cow's milk protein is 80% casein and just 20% whey. The ability of casein to bind calcium and phosphorus is responsible for milk's reputation as a good source of these vital minerals.

Casein is a milk protein that's produced by mammals.

How Casein Works

As a protein supplement, casein supplies our muscles with the full range of amino acids required for exercise recovery and strength building. After a challenging workout, our bodies repair the small tears created in our muscle fibers to build them back to become bigger and stronger.

Proper sleep and adequate protein intake are critical for muscle recovery. Casein products work by providing an extra boost of protein to support muscle tissue.


In its isolated form, casein is used as a primary component in cheese-making and as a protein supplement. Bodybuilders may ingest casein products immediately after a workout or before going to bed to promote exercise recovery. Casein is also used to create infant formulas as a substitute for breast milk.

In addition to various food uses, paint thinner, glues, and plastics may also contain casein. For added protection from water damage, manufacturers coat book pages and illustrations in pigmented casein. Textile producers also use casein solutions to form wool-like fibers to make clothing and other materials.

Structure and Properties

In nature, casein exists as a molecule that's suspended in a surrounding liquid. This structure is called a micelle. You may picture a micelle as an intact little bubble, mixed into a solution.

There are four subtypes of casein. These include:

  • aS1-Casein
  • aS2-Casein
  • b-Casein
  • k-Casein

The first three casein subtypes are calcium-sensitive (all except for k-casein). Calcium-sensitive subtypes bind calcium and phosphorus, carrying these minerals along for digestion and absorption in the body. k-Casein serves a structural function in the casein micelle—keeping the micelle intact until digestive enzymes remove it.

Once k-casein is gone, the micelle curdles into an insoluble mass. This initial step of digestion actually transforms casein into a form that's more resistant to breakdown. Because micelles require several steps for disassembly, casein is considered a slow-digesting protein.


For adults, a casein-based protein shake combined with regular resistance training isn't just a good strategy for building strong muscles, but also solid bones. A cup of non-fat milk has about 300 milligrams (mg) of calcium, much of which is found within the casein micelles.

Most adults require between 1,000 mg to 1,200 mg of calcium per day. Given the dual importance of adequate calcium and protein intake for bone health, casein-rich foods may help support your body in the prevention of osteoporosis.

In addition to serving as a complete protein, casein also benefits bodybuilders because of its slow digestibility. Soy protein and whey protein are released into the bloodstream quickly, while casein takes about six to seven hours to digest fully.

Casein's reduced rate of digestion steadily supplies amino acids to damaged muscle tissue for an extended time after a workout, promoting better recovery. Slow digestion also contributes to casein's ability to promote satiety, helping you feel full for longer and curb unhealthy food cravings.


Cow's milk is one of the top eight food allergens, a fact that poses a problem for formula-fed infants. Doctors typically identify milk allergies in babies and young children, but they can also develop later in life.

If babies are allergic to cow's milk, their doctor may suggest a hydrolyzed casein-based formula. Although its bitter taste isn't always well-tolerated, hydrolyzed casein can help babies with allergies get the nutrients needed during critical growth periods.

If you have an allergy to milk, ask your doctor about specific testing to detect the specific proteins responsible for your allergy. It's possible to be allergic to other proteins in milk, like whey, but not casein.

Nonetheless, it's best to play it safe. See an allergist to help determine the root cause of your milk allergy before risking your luck with casein.

Allergic reactions to milk should not be confused with lactose intolerance. Many people are intolerant to lactose (milk's natural sugar) but will tolerate the casein in yogurt or cheese just fine. An allergy to cow's milk is more likely to cause symptoms like hives, chest tightness, or dizziness, whereas lactose intolerance usually results in diarrhea.

For years, researchers have suspected a potential relationship between casein consumption and autism spectrum disorders. Parents and caregivers often provide variations of casein-free meal plans to children with autism in an attempt to encourage typical development and reduce challenging behaviors.

Some families claim significant behavioral improvements while adhering to a casein-free meal plan, but the evidence is still largely inconclusive. As a result, it's not accurate to assume that casein is a cause for concern in children with autism.

The popularity of casein supplements for the average adult might be more hype than it's worth. For most people, protein deficiency is rare, and supplements are unnecessary.

If your goal is to build muscle and reducing excess body fat, you might want to think twice about that extra protein shake, whether its casein-based or not. When a body get more calories than needed, body fat tends to accumulate. Unhealthy weight gain is possible, even if the extra calories come from protein.

It's also worth noting that high protein intakes from casein or other supplements can be dangerous for some individuals, particularly those with impaired kidney function. Adding a protein supplement can put dangerous stress on already-weakened kidneys.

Before taking casein or any high-protein products, it never hurts to run it by your doctor.


Despite its muscle-building benefits, casein is not considered a performance-enhancing drug. Casein's natural presence in dairy classifies it as a food product, even when taken in supplement form.

Casein can support athletes in reaching new fitness goals without running the risk of the legal ramifications associated with steroids or stimulants.

A Word From Verywell

Casein offers several benefits, especially for infants and adults who do resistance training. A casein supplement can support muscle growth, but in many cases, it's not necessary. If your meal plan includes high-quality protein from food sources like eggs, meat, seafood, or soy, there's a good chance you're already getting what you need.

Nonetheless, for those trying to gain weight or struggling with a poor appetite, a casein-based protein supplement might be a great choice. Only you (and your doctor) can decide which foods and supplements will best support your unique needs.

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