Whey & casein: milking the facts

A brief Q&A article about the key proteins found in milk.

What are casein and whey?

Casein and whey are the two major protein groups of cow’s milk. Casein accounts for nearly 70-80% of total protein in cow’s milk, while whey accounts for the remainder. Both casein and whey are complete, high-quality proteins. Whey protein induces a sharp, rapid increase of plasma amino acids following ingestion, while the consumption of casein elicits a moderate, sustained increase in plasma amino acids.1

Are the casein and whey in human and cow milk the same?

In human milk, the concentration of whey proteins decreases from early lactation and continues to fall. These changes result in a whey protein/casein ratio of about 90:10 in early lactation, 60:40 in mature milk and 50:50 in late lactation.2

The protein profiles of human milk and cow’s milk are different not only in the whey/casein ratio, but also in the types of whey and casein. Human whey contains a significant amount of lactoferrin versus cow’s whey which contains very little lactoferrin. In addition, the major protein fraction of cow’s whey is betalactoglobulin while human whey does not contain any betalactoglobulin. Human casein is also very different than cow’s casein. The caseins in human milk are β- and κ-casein; but α-casein which is regularly found in bovine milk, seems to be absent in human milk.3

Which is better for the infant: a casein- or whey-predominant formula?

There is no convincing evidence on the advantage of whey predominant formulas compared to casein predominant formulas. Growth studies did not show any difference between infants fed with whey predominant or casein predominant formulas.4,5

No international regulatory or scientific body recommends any specific ratio for whey and casein in infant formulas for full-term infants. For example, the CODEX Standard for Infant Formula and the European Society for Paediatric Gastroenterology, Hepatology and Nutrition (ESPGHAN) only recommend that infant formulas should provide at least the amino acid levels in human milk, to supply adequate amounts of dietary indispensable and conditionally indispensable amino acids to meet physiological needs.6,7


References
1. Campbell B, et al. International Society of Sports Nutrition position stand: protein and exercise. J Int Soc Sports Nutr 2007;4:8.
2. Kunz C, Lonnerdal B. Re-evaluation of the whey protein/casein ratio of human milk. Acta Paediatr 1992;81:107-12.
3. Rudloff S, Kunz C. Protein and nonprotein nitrogen components in human milk, bovine milk, and infant formula: quantitative and qualitative aspects in infant nutrition. J Pediatr Gastroenterol Nutr 1997;24:328-344.
4. Harrison GG, et al. Growth and adiposity of term infants fed whey-predominant or casein predominant formulas or human milk. J Pediatr Gastroenterol Nutr. 1987;6:739-747.
5. Lonnerdal B, Chen CL. Effects of formula protein level and ratio on infant growth, plasma amino acids and serum trace elements. I. Cow’s milk formula. Acta Paediatr Scand. 1990;79:257-265.
6. CODEX. Standard for infant formula and formulas for special medical purposes intended for infants. Vol CODEX STAN 72-1981. CODEX: CODEX; 2007.
7. Koletzko B, et al. Global standard for the composition of infant formula: recommendations of an ESPGHAN coordinated international expert group. J Pediatr Gastroenterol Nutr 2005;41:584-599.


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