Casein Protein and Sleep

casein protein and sleep

Casein Protein and Sleep

Casein Protein and Sleep

Casein protein has long been known as the “slow” or “nighttime” protein because of its relatively slower travel time compared to other options. While whey protein is digested very quickly and typically used after a workout, casein takes longer to digest. This makes it, at least hypothetically, a great option as a nighttime/pre-sleep snack.


Benefits of Protein at Night

There are many benefits of consuming a high protein snack before sleep. Research suggests that low calorie, protein rich options can be beneficial to metabolism, health, and body composition when consumed within 30 minutes sleep. Casein protein can increase protein synthesis, satiety, resting energy expenditure, and decrease body fat when used as a pre-sleep snack1.

Why casein at night?

Amino acids from proteins are absorbed into the blood at different rates. Whey produces a quick rise in amino acids followed by a quick decrease back to baseline levels. This process takes approximately three hours. Casein causes a much slower rise and fall with levels of amino acids returning to their baseline about seven hours after consumption. Casein protein takes more than twice as long for the body to fully process than whey2.

An increase in circulating amino acids at night is important in muscle adaptation to training. Increased levels of amino acids cause an increase in muscle protein synthesis. Research suggests consuming nighttime casein leads to strength and muscle gains when combined with resistance training. One study showed muscle protein synthesis rates increased 55% with an adequate amount of protein before sleep2.

Let’s take a look at what the research says about casein and sleep.

Casein Protein: Morning vs Evening

In the first study, researchers wanted to compare the effects of casein protein taken in the morning or evening on body composition and exercise performance. The participants were split up into two groups. The morning group consumed 54 grams of protein before noon. The evening group consumed 54 grams of protein 90 minutes before going to bed. The subjects continued to follow their own exercise programs2.

Over the course of this 8 week study, the evening group saw slightly better results. The morning group saw a 0.7% increase in lean body weight while the evening group saw a 2% increase. The morning group did not see any change in body fat while the evening group saw a 1.8% decrease2.

The next study also compared the effects of morning and evening casein consumption on body composition and strength. In this study, participants were split into morning and evening groups. Both groups consumed 35 grams of casein at their assigned times3.

The morning group saw a 0.8% decrease in body fat percentage while the evening group saw a decrease of 0.4%. The morning group saw a 4.8% increase in lean body mass while the evening group saw a 3.4% increase. The performance gains were mixed with both groups seeing increases on multiple measures of strength3.

The Bottom Line

Generally, whey is known as the post-workout protein while casein is known as the nighttime protein. When looking at how these proteins are digested, this characterization makes sense. In the previous article in this series, we looked at whether casein was a good post-workout protein option. The research found that whey and casein were actually similar in their post-workout effects.

The research above points a similar picture of casein as a nighttime option. There are plenty of studies outlining the benefits of consuming protein at night. As far as real-world benefits in terms of performance and body composition gains, it doesn’t seem to matter when you consume casein protein. Both groups saw improvements regardless of timing. The more important factor is combining resistance exercise with protein.

For the average person, it probably doesn’t matter what type of protein is consumed at specific times of the day. Flavor, cost, availability, and taste might be more important when choosing the right protein.


  1. Kinsey, A., Cappadona, S., Panton, L., Allman, B., Contreras, R., Hickner, R., Ormsbee, M. (2016). The Effect of Casein Protein Prior to Sleep on Fat Metabolism in Obese Men. Nutrients, 8(8), 452. doi:10.3390/nu8080452
  2. Antonio, J., Peacock, C. (2017). Casein Protein Supplementation in Trained Men and Women: Morning versus Evening. International Journal of Exercise Science, 10(3), 479-486.
  3. Joy, J. M., Vogel, R. M., Broughton, K. S., Kudla, U., Kerr, N. Y., Davison, J. M., Dimarco, N. M. (2018). Daytime and nighttime casein supplements similarly increase muscle size and strength in response to resistance training earlier in the day: A preliminary investigation. Journal of the International Society of Sports Nutrition, 15(1). doi:10.1186/s12970-018-0228-9