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Newborn (0-12 months)

What Is Whey Vs Casein: Understanding The Ratio

Written by: Biostime Nutrition

For parents, giving their baby the very best in infant nutrition to match their dietary needs is important. With the different types of ingredients, ratios and also information around breastfeeding, finding the right information is no easy task. 

Whey casein ratios are particularly important when it comes to infant nutrition as they both play an important role in growth and development. 

So, what’s better; higher whey or higher casein? Here’s everything you need to know about the difference between whey and casein. 

Casein vs whey: what’s the difference?

Protein and amino acids are essential for healthy growth and development, which is why there is so much focus on protein levels for infants in their first 12 months of life1

Both whey and casein support growth and development, and are the major proteins found in mammalian milks, including cows milk and human breast milk2

The main difference between casein and whey is the function they provide for growing infants. Whey protein has been found to help increase muscle protein3 and support infant growth4 - especially in their early years. Casein, on the other hand, plays a role in helping build healthy bones through helping to bind calcium and phosphorus5.  While whey and casein have different functions, it’s important to note that each plays an important role in infant health and development.

What is Casein?

Caseins are the most abundant group of proteins in milk, making up about 80% of the proteins in cow’s milk6. The body will typically absorb casein slower than whey, breaking down the protein into small amino acids that circulate in your bloodstream7

Casein is a major protein for infant nutrition and is found in breast milk. It plays an important role in supporting infant growth and development. As casein is a slow-digesting protein7, it can help keep your baby feeling fuller for longer. 

Is Casein in breast milk? 

Yes, casein is in breast milk. However, it’s important to note that the amount of casein in the milk can change. The percentage of  Casein in breast milk changes depending on the lactation period and can range from 20% in early stages to 45% in later stages8. You may notice changes in your baby’s digestion depending on the stage of milk production. 

What is Whey?

Like casein, whey is another important protein for infant development. Whey contains something called immunoglobulins -  which are antibodies that help boost your immune system9

Whey protein helps to support the growth and development of infants’ bones, hair, teeth, muscles and immune system. Unlike casein, whey remains a liquid in an infant’s stomach making whey easier to digest10, especially in those early newborn days.

The Whey Casein ratio

So what exactly is the whey/casein ratio? The whey/casein ratio simply refers to the ratio of whey protein to casein protein in breast milk or other types of infant nutrition. Breast milk typically has a ratio of 40% casein to 60% whey10. However, it’s important to remember the ratio of whey to casein in breast milk does change depending on the stage of the lactation cycle. In early lactation, the ratio will often fluctuate between 30/70 and 20/80. During late lactation, this will typically decrease to an even split of 50/5010

Are babies more sensitive to Whey or Casein? 

Another thing to consider with casein protein vs whey is that babies tend to be more sensitive to casein than whey. This can be down to the fact that casein binds together and forms curds in the stomach, which can make it a little harder to digest10. Whey, on the other hand, stays in liquid form. Keep in mind that all babies are different, so it’s important to take note of how they tolerate each feed. 

It’s important to note that some labels on infant formula may include the whey-to casein ratio on nutritional information, so it’s always best to read the label of the specific product. 

Remember, it’s always important to talk to your healthcare provider if you have any specific questions about your baby’s nutrition. 


  1. ‌Nutten S. Proteins, Peptides and Amino Acids: Role in Infant Nutrition. Protein in Neonatal and Infant Nutrition: Recent Updates [Internet]. 2016;86:1–10. Available from:
  2. Newmark L. Milk Casein Proteins: Ancient, Diverse, and Essential [Internet]. International Milk Genomics Consortium. 2018. Available from:
  3. Jj H, Cm L, Jr S. Effect of Protein/Essential Amino Acids and Resistance Training on Skeletal Muscle Hypertrophy: A Case for Whey Protein [Internet]. Nutrition & metabolism. 2010. Available from:
  4. Picaud JC, Pajek B, Arciszewska M, Tarczón I, Escribano J, Porcel R, et al. An Infant Formula with Partially Hydrolyzed Whey Protein Supports Adequate Growth and Is Safe and Well-Tolerated in Healthy, Term Infants: A Randomized, Double-Blind, Equivalence Trial. Nutrients. 2020 Jul 13;12(7):2072.
  5. Cross KJ, Laila Huq N, Palamara JE, Perich JW, Reynolds EC. Physicochemical Characterization of Casein Phosphopeptide-Amorphous Calcium Phosphate Nanocomplexes*. Journal of Biological Chemistry [Internet]. 2005 Apr;280(15):15362–9. Available from:
  6. Bhat MY, Dar TA, Rajendrakumar Singh L. Casein Proteins: Structural and Functional Aspects [Internet]. IntechOpen; 2016. Available from:
  7. Dangin M, Boirie Y, Guillet C, BeaufrèreB. Influence of the Protein Digestion Rate on Protein Turnover in Young and Elderly Subjects. The Journal of Nutrition. 2002 Oct 1;132(10):3228S3233S.
  8. ‌Martin C, Ling PR, Blackburn G. Review of Infant Feeding: Key Features of Breast Milk and Infant Formula. Nutrients [Internet]. 2016 May 11;8(5):279. Available from:
  9. Ng TB, Cheung RCF, Wong JH, Wang Y, Ip DTM, Wan DCC, et al. Antiviral activities of whey proteins. Applied Microbiology and Biotechnology. 2015 Jul 22;99(17):6997–7008.
  10. Martin C, Ling PR, Blackburn G. Review of Infant Feeding: Key Features of Breast Milk and Infant Formula. Nutrients [Internet]. 2016 May 11;8(5):279. Available from:

Biostime Nutrition - Author

Newborn (0-12 months)