Meet an iconic pair of milk proteins – whey and casein. When it comes to proteins, milk proteins are probably the best studied proteins in relation to exercise and their potential to help build and maintain muscle. About 80% of the protein found in milk is casein and the remaining 20% is whey. Both are high-quality proteins, as they provide all the essential amino acids in quantities high enough to satisfy nutritional needs (1, 2).

Whey and casein are often consumed together, but they are very different to each other. Whey protein is soluble in water, mixes easily and is rapidly digested and absorbed. That is why the concentration of amino acids in your blood increases rapidly after you consume whey (3). Whey is also very high in the essential amino acid leucine, a potent stimulator of muscle protein synthesis (2, 4).

In contrast, casein is not soluble in water and forms clots in the gut (like when you are making cheese).  As a result, it is slowly digested and absorbed by your body (3, 5). For this reason, the amino acid concentration in your blood slowly increases after you ingest casein, but remains elevated for much longer (3).

Which one is better at kickstarting the muscle-building process after your workout? Most studies suggest that it’s whey and not the slower-digesting casein (1, 4, 6-9). This is because whey is considered to be the king of proteins due to its optimal amino acid content and rapid absorption (2, 4).

Recent studies have suggested that if you take casein before going to bed – due to its slow and sustained release of amino acids – it may aid muscle growth and recovery while you sleep (10-13).

Consuming high-quality proteins in milk is an excellent way to support muscle growth and recovery from exercise. Milk protein, as a whole, is also effective in stimulating the muscle-building process (14-16). Its high casein content may help as a pre-sleep protein snack (2). Dairy products such as milk, yoghurt and cheese, not only provide your body with high-quality proteins, but also a range of other nutrients that are important for your health (17).

References

1. Jager R, Kerksick CM, Campbell BI, Cribb PJ, Wells SD, Skwiat TM, et al. International Society of Sports Nutrition Position Stand: protein and exercise. J Int Soc Sports Nutr. 2017;14:20.
2. Devries MC, Phillips SM. Supplemental protein in support of muscle mass and health: advantage whey. J Food Sci. 2015;80 Suppl 1:A8-a15.
3. Boirie Y, Dangin M, Gachon P, Vasson MP, Maubois JL, Beaufrère B. Slow and fast dietary proteins differently modulate postprandial protein accretion. Proc Natl Acad Sci U S A. 1997;94(26):14930-5.
4. van Vliet S, Burd NA, van Loon LJ. The Skeletal Muscle Anabolic Response to Plant- versus Animal-Based Protein Consumption. J Nutr. 2015;145(9):1981-91.
5. Wilson J, Wilson GJ. Contemporary issues in protein requirements and consumption for resistance trained athletes. J Int Soc Sports Nutr. 2006;3(1):7-27.
6. Tang JE, Moore DR, Kujbida GW, Tarnopolsky MA, Phillips SM. Ingestion of whey hydrolysate, casein, or soy protein isolate: effects on mixed muscle protein synthesis at rest and following resistance exercise in young men. J Appl Physiol (1985). 2009;107(3):987-92.
7. Burd NA, Yang Y, Moore DR, Tang JE, Tarnopolsky MA, Phillips SM. Greater stimulation of myofibrillar protein synthesis with ingestion of whey protein isolate v. micellar casein at rest and after resistance exercise in elderly men. Br J Nutr. 2012;108(6):958-62.
8. Pennings B, Boirie Y, Senden JM, Gijsen AP, Kuipers H, van Loon LJ. Whey protein stimulates postprandial muscle protein accretion more effectively than do casein and casein hydrolysate in older men. Am J Clin Nutr. 2011;93(5):997-1005.
9. Miller PE, Alexander DD, Perez V. Effects of whey protein and resistance exercise on body composition: a meta-analysis of randomized controlled trials. J Am Coll Nutr. 2014;33(2):163-75.
10. Trommelen J, Kouw IWK, Holwerda AM, Snijders T, Halson SL, Rollo I, et al. Presleep dietary protein-derived amino acids are incorporated in myofibrillar protein during postexercise overnight recovery. Am J Physiol Endocrinol Metab. 2018;314(5):E457-e67.
11. Snijders T, Res PT, Smeets JS, van Vliet S, van Kranenburg J, Maase K, et al. Protein Ingestion before Sleep Increases Muscle Mass and Strength Gains during Prolonged Resistance-Type Exercise Training in Healthy Young Men. J Nutr. 2015;145(6):1178-84.
12. Res PT, Groen B, Pennings B, Beelen M, Wallis GA, Gijsen AP, et al. Protein ingestion before sleep improves postexercise overnight recovery. Med Sci Sports Exerc. 2012;44(8):1560-9.
13. Trommelen J, van Loon LJ. Pre-Sleep Protein Ingestion to Improve the Skeletal Muscle Adaptive Response to Exercise Training. Nutrients. 2016;8(12).
14. Mitchell CJ, McGregor RA, D'Souza RF, Thorstensen EB, Markworth JF, Fanning AC, et al. Consumption of Milk Protein or Whey Protein Results in a Similar Increase in Muscle Protein Synthesis in Middle Aged Men. Nutrients. 2015;7(10):8685-99.
15. Gorissen SHM, Witard OC. Characterising the muscle anabolic potential of dairy, meat and plant-based protein sources in older adults. Proc Nutr Soc. 2018;77(1):20-31.
16. Traylor DA, Gorissen SHM, Hopper H, Prior T, McGlory C, Phillips SM. Aminoacidemia following ingestion of native whey protein, micellar casein, and a whey-casein blend in young men. Appl Physiol Nutr Metab. 2019;44(1):103-6.
17. Tunick MH, Van Hekken DL. Dairy Products and Health: Recent Insights. J Agric Food Chem. 2015;63(43):9381-8.