The Differences Between Casein & Whey + How To Choose

You've likely heard of the two types of protein found in dairy milk: casein and whey. But have you ever considered which one is better for you?

Whey protein is the liquid left over when milk is processed to make cheese or yogurt. This high-quality protein comprises 20% of the protein1 found in dairy milk.

Since whey protein is a complete protein source2 that contains all nine essential amino acids, it's readily digested and easily put to work1 in the body. In addition, whey protein's water-solubility3 allows it to mix well with water, milk, coffee, or other beverages.

The two main types of whey are whey protein concentrate and whey protein isolate, which is lower in lactose but has a higher protein concentration. (Learn more about the differences between the two here.)

Casein is the primary protein in dairy milk, making up 80% of its protein content1.

Casein is produced when curds containing the protein are separated from the rest of the milk during acidification4—a process performed on dairy milk to inhibit the growth of harmful bacteria and extend its shelf life.

Like whey, casein is a high-quality complete protein containing all nine essential amino acids2. However, casein is water-insoluble and coagulates in the stomach. This process slows gastric emptying5, making it less digestible and slower to absorb than whey.

Casein occurs in several genetically determined forms, including A1 and A2 variants, explains Svetlana Nepocatych, Ph.D., RDN, a registered dietitian nutritionist and associate professor at the Elon University Department of Exercise Science.

"The A1 and A2 casein variants differ in their amino acid composition6, leading to changes in the structure of the casein protein," Nepocatych says.

While research remains inconclusive on if one protein source is more beneficial to strength-training athletes, one study that looked at bodybuilders found an increase in strength gains9 in the whey supplement group. Whey protein has also been shown to enhance muscle recovery10 after resistance training.

It is important to note that "Whey protein ingestion stimulates greater muscle protein synthesis (MPS)11 compared to casein," says Nepocatych. This is because whey contains nearly 33% more leucine12—a branched-chain amino acid that promotes muscle growth—than casein.

For years, experts have recommended consuming protein within a post-exercise anabolic window14 of 30 to 120 minutes to optimize skeletal muscle growth and fat-burning. However, more recent research15 has indicated that protein timing isn't as critical as we initially thought.

So instead of feeling the need to slam a whey protein shake after your workout, you can just eat protein throughout the day to promote muscle growth. Most experts agree that eating 25 to 30 grams of high-quality protein in each meal is a solid strategy for filling your daily protein needs (typically at least 100 grams per day for active people).

If your health goal is to lose weight (specifically fat), upping your protein intake can help you reach it. "Increasing protein intake during periods of calorie restriction would benefit someone trying to lose weight," says Nepocatych. "Both muscle and fat mass are lost during weight loss. Therefore, higher protein intake [throughout the day] will help to preserve muscle mass and burn more calories."

Casein may be a better option for weight loss since it's slower to digest and can keep you feeling full longer. In addition, research reveals that whey is more satiating in the short term, whereas casein is more satiating in the long term16.

If you're supplementing with whey or casein protein, you'll want to make sure to pick a product that is tested for purity and potency through third-party labs. Additional certifications include those from Informed Sports, the National Sanitation Foundation (NSF), and USP verified.

Transparency is also key, and you'll want to look for a company that shares the amino acid profile of its products. Avoid extra sugars and additives, and opt for more sustainable USDA-certified organic or certified grass-fed proteins whenever you can.

Whey protein is a fast-digesting dietary protein supplement rapidly absorbed by your body. Casein protein is slower to digest and absorb in the bloodstream but is more satiating in the long term.