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The Differences Between Casein & Whey + How To Choose

Adam Meyer
Author: Expert reviewer:
Updated on April 24, 2023
Adam Meyer
Certified holistic nutritionist
By Adam Meyer
Certified holistic nutritionist
Adam Meyer is a health writer, certified holistic nutritionist, and plant-based athlete
Lauren Torrisi-Gorra, M.S., RD
Expert review by
Lauren Torrisi-Gorra, M.S., RD
Registered Dietitian
Lauren Torrisi-Gorra, MS, RD is a registered dietitian, chef, and writer with a love of science and passion for helping people create life-long healthy habits. She has a bachelor’s degree in Communication and Media Studies from Fordham University, a Grand Diplôme in Culinary Arts from the French Culinary Institute, and master's degree in Clinical Nutrition and Dietetics from New York University.

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?

Here's a science-backed guide to whether casein or whey is superior for muscle growth, the optimal time to take protein, and tips for choosing the best casein and whey protein powders.

Whey protein overview

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.)

Whey is a popular type of protein powder supplement. Head to any grocery store or health shop and you'll probably find whey protein available in a few flavors at reasonable prices.


Whey protein is a complete protein source that makes up one-fifth of dairy milk protein. It's easy to digest and water-soluble, allowing rapid absorption in the bloodstream and muscle.

Casein protein overview

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 protein powders mix well with water and other beverages despite its water-insolubility. However, casein protein supplements are more expensive, and some users report that whey tastes better than casein.

A1 vs. A2 casein

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.

Research on these two casein forms is limited, but it suggests that A2 is less inflammatory7 and elicits less gastrointestinal (GI) sensitivity than A1. Therefore, if you have casein sensitivity and experience GI distress from casein protein powders but not other dairy products, consider using the A2 variant or supplementing with whey protein instead.


Casein protein is a complete protein source that comprises 80% of dairy milk protein. It's water-insoluble and slows gastric emptying, making it less digestible and slower to absorb than whey. There are multiple kinds of casein protein, and research shows that A2 is less inflammatory and less likely to cause GI sensitivity than A1.

How to choose which one is right for you

Both casein and whey are high-quality complete protein sources containing the branched-chain amino acids (BCAAs) leucine, isoleucine, and valine8, making them excellent choices for muscle growth and repair when paired with resistance training. 

If you want to build muscle: Whey

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.

"In whey protein, leucine is about 12%, so 23 grams of whey protein isolate will trigger it," Don Layman, Ph.D., a leading protein and amino acid researcher, previously told mindbodygreen.

If you're sensitive to dairy: Whey (isolate)

Whey and casein can be used interchangeably by the average person searching for a high-quality protein source. However, if you're lactose-intolerant or sensitive to dairy, consider supplementing with a whey protein isolate since it contains less than 1% lactose13 and causes less GI distress than casein. Conversely, casein is a better option if you have a whey allergy.

If you're looking for a protein powder that will fill you up: Casein

Since casein has a slower digestion rate than whey, it's better at promoting satiety and increasing feelings of fullness.

If you're vegan: Neither

Whey and casein protein powders are not suitable for vegans, who will want to opt for a plant protein powder instead.


Both casein and whey are high-quality protein sources that contain BCAAs for optimal muscle growth and recovery. Whey protein stimulates greater muscle protein synthesis and has fewer GI side effects, while casein is more filling.

When to take whey and casein protein to get the best results

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.

It's best to get most of your protein from whole-food sources, but whey and casein protein powders can help you fill gaps where needed so you can make sure your body is getting the protein it needs.


Instead of consuming protein only after workouts, aim to get 25 to 30 grams of high-quality protein three to four times daily for optimal muscle growth and fat loss.

How to choose the best product

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.

Here's a quick list of what to look for in a whey or casein protein product:

Frequently Asked Questions

Can you take casein every day?

Casein protein is safe to take daily. However, protein powder supplements should only be used as the name suggests—to supplement an already healthy and protein-rich diet.

Which protein is best for muscle gain?

Both casein and whey are high-quality proteins that promote muscle growth when paired with resistance training. However, research indicates that whey protein may have a slight edge due to the fact that it has a quicker absorption rate, is easier to digest, and is more efficient at building and maintaining muscle mass and enhancing muscle recovery.

Which protein is best for fat loss?

Whether whey or casein, protein is a highly satiating macronutrient that can benefit weight loss efforts. With that said, casein may be a better option for weight loss since it's slower to digest and more satiating in the short term.

The takeaway

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.

Both whey and casein are high-quality, complete protein sources that can help build skeletal muscle and promote fat loss when paired with resistance training. They can also help you fulfill your daily protein needs if you're unable to do so using whole foods alone.

Adam Meyer author page.
Adam Meyer
Certified holistic nutritionist

Adam Meyer is a health writer, certified holistic nutritionist, and 100 percent plant-based athlete. He graduated from the NutraPhoria School of Holistic Nutrition in 2019 and has since founded Pillars Nutrition. His work has been featured on EatingWell, Eat This Not That!, The Beet, Verywell Fit, The Healthy, Livestrong, Alive, Best Life and others.

Adam lives in British Columbia, Canada, with his wife, two kids and an Australian shepherd. That's where you can find him running mountain trails, working out in his home gym, or writing in a coffee shop.