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Cow milk protein is 80% casein and 20% whey protein. In your stomach, casein forms a gel and thus digests slowly. The protein in cheese is mostly casein.

Our evidence-based analysis on casein features 35 unique references to scientific papers.

Research analysis led by and reviewed by the Examine team.
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Research Breakdown on Casein

1Source and Components


Casein is a protein that is derived from the milk of many species; most human consumption of casein comes from bovine (cow) milk.

Casein is the insoluble portion of the milk, whereas whey is the soluble portion; the amount of casein in standard milk protein is approximately 80%, and human milk is variable depending on time spent lactating.[1][2][3][4]


Casein protein, like all protein, is a source of dietary amino acids. As it is an animal source, it is complete in the sense that it contains all essential amino acids in adequate enough numbers for proper human functioning at the minimum level of protein intake recommended.

Casein protein also contains various bioactive peptides. These peptides are partially digested in the stomach, and prior to being broken down into their constituent amino acids they are able to exert effects in the intestines (prior to absorption). These effects may be wide-reaching, and are discussed in the following bullets.

2Production of Casein

2.1Standard Processing

Standard processing of casein involves a separation of the two dairy proteins (casein and whey).

Whole milk protein is treated with a compound known as a 'coagulant', usually chymosin[5], which serves to coagulate (congeal, or solidify) the casein fragment. This is a step crucial to cheese making (which requires casein to provide a solid foundation) but is also significant for separating the wheys and casein (curds).[6][7]

With the casein fragment more solid, the whey fragment (still liquid) is then separated from the casein through a process called syneresis. The degree of syneresis varies depending on what the end product (usually cheese) would be, and can be manipulated by salt[8], acidity[9], enzyme treatment[10] and physical disturbances[11] amongst other techniques to provide unique flavor and texture to the end product cheese. Casein protein supplementation is more concerned with the extraction of as much whey as possible, which leaves pure casein protein behind.

2.2Micellar Casein

Micellar casein tends to be produced via microfiltration, which has the ability to concentrate the micellar segments of casein.[12][13]

3List of Peptides in Casein

Casein contains various Bioactive peptides, which can be defined as sequences of amino acids that are contained in dietary proteins and are partially denatured in the stomach to reveal short sequences. These sequences can exert biological effects in the intestines prior to being digested, or may be digested through a peptide transporter.[14]

3.1AlphaS-1 Peptide

When supplemented to women at 150mg daily, the AlphaS-1 peptide is known to produce an anxiolytic effect.[15] Two doses of 200mg may be able to reduce the response to perceived stressors.[16] The anxiolytic effect may also provide better sleep in those with high levels of stress.[17]

Similar to the c12 peptide, AlphaS-1 may also have an ability to induce ACE-inhibitor like effects and reduce blood pressure.[18]

AlphaS-1 is also a peptide that is noted to cause allergies, and thus persons allergic to dairy may also be allergic to this peptide in supplemental form.[19]

3.2c12 Peptide

When administered in the form of tablets, the c12 peptide at a dose of 3.8g daily for 4 weeks is able to reduce blood pressure in pre-hypertensive subjects from an average of 138/87 to 127/80 in one study.[20] This is due to the c12 peptide having the properties of an ACE inhibitor.[21]


Glycomacropeptides can be found in the casein portion of whole milk products, but due to their water soluble nature they leave the casein portion during chymosin treatment at the beginning stages of processing.[22] They do tend to be associated with casein protein as they originate with kappa casein molecules, hence their inclusion in this Examine page. Unless otherwise added afterwards however, they are not a normal component of casein supplementations.

3.4Caseinophosphopeptides (CPPs)

3.5Casoxins and Casomorphins

Casoxins and Casomorphins are peptides which are able to act on the opioid system, which is involved in the rate of digestion. The class of casomorphins are opioid agonists (activators) and the casoxins opioid antagonists.[23]

Casein seems to have a higher relative content of casomorphins to casoxins, which may explain the reduced transit speed after consumption (as activation of the opioid system reduces intestinal motility).[24]

4Casein Hydrolysate (Hydrolyzed Casein)

4.1Digestion Speed

4.2Effects on protein synthesis

4.3Neurological Effects

It has been shown to have a more relaxing effect at rest and after mental stress when compared to maltitol,[25] which may be related to a specific tryptic hydrolysate found in bovine casein.[26] This AlphaS1 peptide has been shown to reduce stress when ingested by women at 150mg daily.[15]


  1. ^ Kinsella JE. Milk proteins: physicochemical and functional properties. Crit Rev Food Sci Nutr. (1984)
  2. ^ Lönnerdal B, Forsum E. Casein content of human milk. Am J Clin Nutr. (1985)
  3. ^ Kunz C, Lönnerdal B. Re-evaluation of the whey protein/casein ratio of human milk. Acta Paediatr. (1992)
  4. ^ Belloque J, Ramos M. Determination of the casein content in bovine milk by 31P-NMR. J Dairy Res. (2002)
  5. ^ Kumar A, et al. Chymosin and other milk coagulants: sources and biotechnological interventions. Crit Rev Biotechnol. (2010)
  6. ^ Johnson ME, Lucey JA. Major technological advances and trends in cheese. J Dairy Sci. (2006)
  7. ^ Huffman LM, Harper WJ. Maximizing the value of milk through separation technologies. J Dairy Sci. (1999)
  8. ^ Pastorino AJ, Hansen CL, McMahon DJ. Effect of salt on structure-function relationships of cheese. J Dairy Sci. (2003)
  9. ^ Pastorino AJ, Hansen CL, McMahon DJ. Effect of pH on the chemical composition and structure-function relationships of cheddar cheese. J Dairy Sci. (2003)
  10. ^ Lilbaek HM, et al. Improving the yield of Mozzarella cheese by phospholipase treatment of milk. J Dairy Sci. (2006)
  11. ^ Everard CD, et al. Effects of cutting intensity and stirring speed on syneresis and curd losses during cheese manufacture. J Dairy Sci. (2008)
  12. ^ Microfiltration in Cheese and Whey Processing.
  13. ^ Solanki G, Rizvi SS. Physico-chemical properties of skim milk retentates from microfiltration. J Dairy Sci. (2001)
  14. ^ Muro Urista C, et al. Review: Production and functionality of active peptides from milk. Food Sci Technol Int. (2011)
  15. ^ a b Kim JH, et al. Efficacy of alphas1-casein hydrolysate on stress-related symptoms in women. Eur J Clin Nutr. (2007)
  16. ^ Messaoudi M, et al. Effects of a tryptic hydrolysate from bovine milk alphaS1-casein on hemodynamic responses in healthy human volunteers facing successive mental and physical stress situations. Eur J Nutr. (2005)
  17. ^ Guesdon B, et al. A tryptic hydrolysate from bovine milk alphaS1-casein improves sleep in rats subjected to chronic mild stress. Peptides. (2006)
  18. ^ Rousseau-Ralliard D, et al. Inhibitory effect of αS1- and αS2-casein hydrolysates on angiotensin I-converting enzyme in human endothelial cells in vitro, rat aortic tissue ex vivo, and renovascular hypertensive rats in vivo. J Dairy Sci. (2010)
  19. ^ Schulmeister U, et al. Cloning, expression, and mapping of allergenic determinants of alphaS1-casein, a major cow's milk allergen. J Immunol. (2009)
  20. ^ Cadée JA, et al. Bovine casein hydrolysate (c12 Peptide) reduces blood pressure in prehypertensive subjects. Am J Hypertens. (2007)
  21. ^ Townsend RR, et al. A randomized, double-blind, placebo-controlled trial of casein protein hydrolysate (C12 peptide) in human essential hypertension. Am J Hypertens. (2004)
  22. ^ Keogh JB, et al. Effect of glycomacropeptide fractions on cholecystokinin and food intake. Br J Nutr. (2010)
  23. ^ Teschemacher H, Koch G, Brantl V. Milk protein-derived opioid receptor ligands. Biopolymers. (1997)
  24. ^ Taché Y, Garrick T, Raybould H. Central nervous system action of peptides to influence gastrointestinal motor function. Gastroenterology. (1990)
  25. ^ Nakamura H, et al. Influences of casein hydrolysate ingestion on cerebral activity, autonomic nerve activity, and anxiety. J Physiol Anthropol. (2010)
  26. ^ Messaoudi M, et al. Anxiolytic-like effects and safety profile of a tryptic hydrolysate from bovine alpha s1-casein in rats. Fundam Clin Pharmacol. (2009)
  27. Macfarlane GT, Macfarlane S. Bacteria, colonic fermentation, and gastrointestinal health. J AOAC Int. (2012)
  28. MacLean DA, Graham TE, Saltin B. Branched-chain amino acids augment ammonia metabolism while attenuating protein breakdown during exercise. Am J Physiol. (1994)
  29. Joint WHO/FAO/UNU Expert Consultation. Protein and Amino Acid Requirements in Human Nutrition. World Health Organ Tech Rep Ser. (2007)
  30. Douglas S Kalman. Amino Acid Composition of an Organic Brown Rice Protein Concentrate and Isolate Compared to Soy and Whey Concentrates and Isolates. Foods. (2014)
  31. Stefan H M Gorissen, et al. Protein Content and Amino Acid Composition of Commercially Available Plant-Based Protein Isolates. Amino Acids. (2018)
  32. EASTOE JE. The amino acid composition of mammalian collagen and gelatin. Biochem J. (1955)
  33. Hays NP, et al. Effects of whey and fortified collagen hydrolysate protein supplements on nitrogen balance and body composition in older women. J Am Diet Assoc. (2009)
  34. Zdzieblik D, et al. Collagen peptide supplementation in combination with resistance training improves body composition and increases muscle strength in elderly sarcopenic men: a randomised controlled trial. Br J Nutr. (2015)
  35. Mathai JK, Liu Y, Stein HH. Values for digestible indispensable amino acid scores (DIAAS) for some dairy and plant proteins may better describe protein quality than values calculated using the concept for protein digestibility-corrected amino acid scores (PDCAAS). Br J Nutr. (2017)