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Overview: Casein protein is one of the two main proteins found in cow’s milk. It is a complete protein that is absorbed slowly by your body. It is often used for various health purposes, but its benefits for any use are not well defined. Common side effects include diarrhea, gas, or an upset stomach, although different forms of casein may cause different side effects. Before taking casein protein, tell your health care provider about all of your health conditions and any medicines or supplements you may be using, especially if you have lactose intolerance or a milk allergy.

Uses

What is casein protein used for?

Casein protein is used for various reasons, although its benefits are not well defined. Some common reasons that people use casein protein include the following.

Note: The FDA has not reviewed casein protein for safety and effectiveness. Learn more about dietary supplements here.

How does casein protein work (mechanism of action)?

Casein protein is a type of protein found in cow’s milk. It is a complete protein, which means it contains all of the amino acids that your body is not able to make on its own. However, it takes many hours for your body to absorb casein protein from your gut, so it is considered a “slow-release” protein. The other protein found in cow’s milk, whey protein, is absorbed quickly by your body and is considered a “quick-release” protein. Milk and most milk-protein products contain both casein protein and whey protein.

Due to its slow absorption into the body, casein protein is thought to help reduce feelings of hunger. It also supports muscles while they are being repaired after a workout. However, the benefits of taking casein protein for these uses are not well defined. Whey protein, on the other hand, is commonly taken before or during a workout to help build muscle. In fact, research shows that taking whey protein can help some people increase muscle strength by a small amount. It is not clear if taking casein protein with whey protein can increase this effect.

Some dietary supplements contain casein hydrolysate (hydrolyzed casein), which is a form of casein that has been broken down into smaller pieces called peptides. These small pieces are absorbed much more quickly from your gut and may also be less likely to cause diarrhea, gas, or an upset stomach in some people. Some research shows that casein hydrolysate supplements may help lower blood pressure by a small amount. However, this change in blood pressure is too small to be meaningful for most people.

There is also interest in taking whole casein protein to improve heart health and reduce weight gain. But most research shows that whole casein protein alone is not helpful for these uses.

How should I store casein protein?

You should store casein protein according to the product label. Most dietary supplements should be kept in a cool, dry location that is out of the reach of children and pets and not in direct sunlight.

Side Effects

What are the most common side effects of casein protein?

The most common side effects of casein protein are listed below. These side effects may vary depending on the dose you are taking or the type of casein protein you are using. Tell your health care provider if you have any of these side effects that bother you.

  • Diarrhea
  • Gas
  • Upset stomach

There may be other side effects of casein protein that are not listed here. Contact your health care provider if you think you are having a side effect of a supplement. In the U.S., you can report side effects to the FDA at www.safetyreporting.hhs.gov or by calling 888-SAFEFOOD (888-723-3366). In Canada, you can report side effects to Health Canada at www.health.gc.ca/medeffect or by calling 866-234-2345.

What are the serious side effects of casein protein?

While less common, the most serious side effects of casein protein are described below, along with what to do if they happen.

Severe Allergic Reactions. Casein protein may cause allergic reactions, which can be serious. Stop taking casein protein and get help right away if you have any of the following symptoms of a serious allergic reaction.

  • Breathing problems or wheezing
  • Racing heart
  • Fever or general ill feeling
  • Swollen lymph nodes
  • Swelling of the face, lips, mouth, tongue, or throat
  • Trouble swallowing or throat tightness
  • Itching or skin rash
  • Bumps on the skin called hives, which can be red, pink, white, or brown depending on your skin tone
  • Nausea or vomiting
  • Dizziness, feeling lightheaded, or fainting
  • Stomach cramps
  • Joint pain

Warnings & Precautions

Who should not use casein protein?

Allergies to Ingredients. People who are allergic to any of the following should not take casein protein.

  • Casein hydrolysate
  • Casein protein
  • Hydrolyzed casein
  • Micellar casein
  • Any of the ingredients in the specific product

Your pharmacist can tell you all of the ingredients in the specific casein protein products they stock.

Milk Allergy. Casein protein is a natural part of cow’s milk. Many people with an allergy to cow’s milk are allergic to casein protein. If you have a milk allergy, you should not take casein protein unless your health care provider tells you it is safe to do so.

What should I know about casein protein before using it?

Casein protein is a dietary supplement. It cannot be marketed to treat or cure a disease.

Read and follow the directions on the specific product you are taking, or take it as recommended by your health care provider.

Keep casein protein out of the reach of children.

Casein protein may be available as hydrolyzed casein (casein hydrolysate) or micellar casein. These two forms of casein protein may have different effects and side effects. Micellar casein is the form naturally found in cow’s milk. It is very large and contains other substances found in milk, such as calcium, phosphorus, and lactose. Due to its large size, micellar casein is absorbed very slowly by your body. Hydrolyzed casein is broken down into small pieces called peptides, which your body absorbs much faster than micellar casein. Read the product label closely to understand which form of casein protein it contains.

If you are using casein protein powder, use an appropriate measuring device to measure the powder, such as the device included with the product. Read the label carefully and measure the amount stated on the label.

The FDA has not tested casein protein products to confirm that they contain the ingredients stated on their labels. Some dietary supplements have been tested by third-party organizations to confirm that they contain the ingredients listed on their labels and do not contain any harmful chemicals. Learn more about how to choose a safe dietary supplement product here.

What should I tell my health care provider before using casein protein?

Tell your health care provider about all of your health conditions and any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using. This will help them know if casein protein is right for you.

In particular, make sure that you discuss any of the following.

Lactose Intolerance. Casein protein comes from cow’s milk, which also contains lactose. Some casein protein products, including micellar casein, may contain lactose in small or large amounts. If you have lactose intolerance, look for products that are labeled as lactose-free.

Other Current and Past Health Conditions. Tell your health care provider if you have any of the following.

Other Medicines and Supplements. Casein protein may interact with other medicines and supplements. Before taking casein protein, tell your health care provider about any prescription or OTC medicines, vitamins/minerals, herbal products, and other supplements you are using. See the Interactions section for more details.

Pregnancy. It is not known if or how casein protein could affect pregnancy or harm a fetus. Tell your health care provider if you are pregnant or plan to become pregnant.

Breastfeeding. It is not known if casein protein passes into breast milk. Tell your health care provider if you are breastfeeding or plan to breastfeed.

Interactions

Does casein protein interact with foods or drinks?

There are no known interactions between casein protein and foods or drinks.

It is unknown if drinking alcohol will affect casein protein.

Does casein protein interact with medicines (drug interactions)?

Always tell your health care provider about any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using.

Casein protein, especially micellar casein, may affect the absorption of some medicines. Tell your health care provider about all medicines that you take or have recently taken.

The interactions between casein protein and medicines are not fully understood. As with most dietary supplements, the research on drug interactions with casein protein is incomplete. Always check with your health care provider before taking casein protein with any medicines.

Overdose/Missed Dose

What should I do if I accidentally use too much casein protein?

If you or someone else has used too much casein protein, get medical help right away, call 911, or contact a Poison Control center at 800-222-1222.

Casein protein is available in different forms and doses. Read the product label closely and speak with a health care provider about how to take casein protein safely. Do not take double or extra doses, even if you miss a dose.