YOU'VE LIKELY HEARD about whey protein and maybe even pea protein, but there's another protein that's popular among the fitness community: casein.

Casein shares more in common with whey than it does with peas, but casein is also distinctly different from both—and has unique benefits.

“There are two different types of protein in cow’s, goat’s and sheep’s milk—casein and whey,” says Kim Yawitz, R.D., a gym owner in St. Louis, MO.

“About 80 percent of the protein in cow’s milk is casein, and about 20 percent of it is whey, according to a study in the Iranian Journal of Pharmaceutical Research,” says Amy Gorin, M.S., R.D.N., an inclusive plant-based dietitian in Stamford, CT and owner of Plant Based with Amy. “Whey and casein are both complete proteins and are different in several ways. For one, whey protein is digested more quickly than casein protein.”

Ahead, the scoop on all things casein protein.

What are casein's benefits?

Here's what supplement manufacturers say: Whey-protein supplements speed the nutrient to your muscles, but casein supplements are marketed as slow digesting. So they deliver a steady supply of protein over time and can help build muscle even while you sleep.

(Some casein products also contain melatonin for better rest.)

But what are the benefits really?

The muscle stuff. A 2021 study review in Nutrients found that people doing resistance training who consumed a casein supplement before bed did gain muscle mass—with little to no effect on metabolism.

measuring spoon with casein protein supplement powder

Casein really does digest more slowly than whey, extending the window for muscle-protein synthesis, according to the review.

Do you need a casein supplement?

You don’t have to chug casein before bed to build muscle overnight. People who spread protein intake throughout the day instead of loading up in one sitting increased muscle mass best overall, that Nutrients review found.

close up on hand of unknown caucasian man holding dark supplement shaker while sitting at gym during training copy space selective focus
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If you can’t hit your daily protein requirement (that’s one gram of protein for every pound of target bodyweight) from food, then sure, says Amy Gorin, R.D.N., a dietitian based in Stamford, Connecticut.

But fair warning: Casein, like whey, is a dairy product.

So if you’re lactose intolerant? Hard pass.

What to look for in a casein supplement

A supplement that has at least 24 grams of protein a serving and is third-party certified by a group like NSF, which helps ensure that it doesn’t contain any banned substances.

And skip the supplements with melatonin, which can actually disrupt your sleep cycles with extended use.

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Perri O. Blumberg

Perri is a New York City-born and -based writer; she holds a bachelor’s in psychology from Columbia University and is also a culinary school graduate of the plant-based Natural Gourmet Institute, which is now the Natural Gourmet Center at the Institute of Culinary Education. Her work has appeared in the New York Post, Men's Journal, Rolling Stone, Oprah Daily,, Architectural Digest, Southern Living, and more. She's probably seen Dave Matthews Band in your hometown, and she'll never turn down a bloody mary. Learn more at