Casein Protein: What's It Good For & Who Should Take It?

Casein protein is a slow-digesting protein commonly found in dairy products. It's popular among athletes and bodybuilders for maximizing muscle growth and recovery. However, like all proteins, casein has pros and cons, and it's essential to understand how it compares to other protein sources. 

Casein protein is a type of protein found in milk and dairy products (it makes up 80% of the protein content1 in dairy milk). It's known for its slow digestion rate2, which means it's absorbed by the body more gradually than other proteins like whey.

Casein protein comes from the curds that form when milk is coagulated, while whey protein comes from the liquid that separates during cheese-making.

Unlike whey protein, casein can take up to seven hours3 for the body to fully break down and absorb. This makes it an ideal protein source for people who want a sustained release of protein throughout the day or night, such as bodybuilders, athletes, and those who exercise regularly.

Casein protein's texture is thicker and creamier than whey protein, with a slightly bland taste. Many people consume casein protein in a protein powder supplement to increase their protein intake and support muscle growth and recovery.

Casein protein has a unique ability to provide a slow and sustained release of amino acids, which can lead to prolonged muscle protein synthesis (MPS) compared to other protein sources like whey.

Casein protein has a slower digestion rate than whey protein, which may make it more suitable for individuals who experience digestive discomfort. This is because casein forms a gel-like substance in the stomach, slowing gastric emptying6 and leading to a delayed release of amino acids.

Research has shown that consuming casein may have blood-pressure-lowering effects. For example, one study found that people who consumed casein protein7 had lower systolic blood pressure, reduced cardiovascular disease risk, and better blood sugar regulation.

Casein is more satiating than other protein sources due to its slower digestion rate and prolonged release of amino acids. One study found that participants who consumed casein protein had lower reported hunger and higher satiety ratings9 than those who consumed whey.

Casein is a complete protein source11, meaning it contains all nine essential amino acids that the body cannot produce on its own. It's also rich in branched-chain amino acids (BCAAs), which play a crucial role in MPS and recovery.

While casein's slow digestion can be an advantage for promoting satiety, it may not be ideal for post-workout recovery. For example, a 2016 study found that whey protein was more effective in promoting MPS13 after exercise.

Though casein is a complete protein and a good source of essential amino acids, it may not be the best choice for those with dairy allergies or lactose intolerance.

A1 and A2 beta-casein are two types of casein proteins found in milk. A1 beta-casein results from a genetic mutation in European cows18, whereas A2 beta-casein is the original protein found in cows from Asia and Africa, as well as most goats and sheep.

"The A1 and A2 casein variants differ in their amino acid composition19, leading to changes in the structure of the casein protein," Svetlana Nepocatych, Ph.D., RDN, a registered dietitian nutritionist and associate professor at the Elon University Department of Exercise Science, previously told mindbodygreen.

Some studies suggest that A2 beta-casein may be easier to digest and less likely to cause gastrointestinal symptoms20, such as bloating and diarrhea, than A1 beta-casein. "A2 casein tends to be less inflammatory and less likely to cause gut issues," functional medicine doctor Mark Hyman, M.D., says on the mindbodygreen podcast.

Ultimately, every protein source has benefits and drawbacks.

Whey protein is an excellent option for those looking for a fast-absorbing, high-quality protein source. Plant-based or vegan protein powders can be a good choice for individuals with dietary restrictions or those seeking a more sustainable protein source21. Casein protein provides a slower release of amino acids and may benefit muscle recovery and growth, particularly when consumed before bed.

Compared to other protein sources, whey protein has a higher concentration of essential amino acids, particularly leucine, which is a key trigger for MPS.

Regarding digestibility, whey protein is often considered the easiest to digest, with a high absorption rate and low likelihood of causing digestive issues.

Casein is found in many dairy products, such as milk, cheese, and yogurt. However, if you're looking for a nondairy source of casein, it can also be found in some protein bars and powders.

While there isn't necessarily a "best" time of day to consume casein, many people take it before bed to promote MPS. Research23 suggests that consuming at least 40 grams of casein before bed can effectively promote MPS at night.

If you are going to use a casein protein powder, look for a brand that's sustainably sourced and low in additives and sugars. A third-party-tested supplement is another important factor to consider to verify the ingredients in the product.

Supplementing with casein protein is considered safe for most people when taken appropriately.

However, some individuals may experience mild side effects24 such as bloating, gas, and gastrointestinal discomfort due to its slow digestion rate. In addition, those with dairy allergies or lactose intolerance should avoid casein protein supplements altogether.

Regarding long-term safety, some studies25 have suggested that high protein intake from casein and other sources may put additional strain on the kidneys and liver in individuals with preexisting kidney or liver conditions. However, more research is needed to fully understand the potential risks.

Casein protein is a slow-digesting protein found in dairy products that's popular among athletes and bodybuilders for maximizing muscle growth and recovery.