Hi All,

Just when I thought I knew it all...

I recently noticed that different lactation texts have different figures for
the whey:casein ratio of human milk, ranging from 80:20 to 60:40. Frustrated
at the different figures, I went to Medline and looked up the original
articles cited in the texts.

AHAH! Current research suggests that the whey:casein ratio in human milk is
NOT the same throughout the lactation cycle. The casein increases in
proportion to the whey over time/during the course of lactation. Early milk
is over 90% whey. Later, the "mature milk" is about 60:40 whey-to-casein. By
the "end" of the lactation cycle, the ratio is about 50:50.

And AHAH again - since the proportion of casein in the milk strongly
influences the texture/composition of the stools, this probably helps
explain why the young breastfed baby poops many times a day. After 6-8
weeks, the poop gets thicker; some babies save it up and deliver the "load"
in larger quantities, but less often. As long as it's still soft and the
baby is otherwise gaining weight and happy, this pattern is normal.

And another AHAH! Taking this a step further: The whey proteins are higher
in immunofactors, which are more important to the younger baby whose own
immune system is less mature. As the baby matures, he becomes more
physically mobile therefore needing more calcium (from the casein) for bone
mineralization. Once again, mother's milk composition is perfect for the
changing needs of the infant!

The citation is Kunz C, Lonnerdal B. Re-evaluation of the whey
protein/casein ratio of human milk. Acta Paediatr 1992 Feb; 81(2):107-12.
Lonnerdal is co-author on many of the earlier articles on whey:casein ratio
and milk composition.

Linda J. Smith, BSE, FACCE, IBCLC
Bright Future Lactation Resource Centre
Dayton, OH USA
http://www.bflrc.com