Iron is more completely absorbed from breastmilk than from formula, this has been known for some years. I am away from home and cannot give you exact references right now, but I am sure that you could find the information from Google Scholar. There are also differences in the way other nutrients are used - for example fats are more completely digested because breastmilk contains bile-salt stimulated lipase; essential fatty acids may be used differently, depending on which position they are incorporated in the triglyceride molecule, protein is more completely used as the amino acid pattern is exactly what the baby needs, and in the same proportion to build the body tissues without waste; casein molecules are very different, and those in cow's milk bind calcium differently; oligosaccharides are more suitable for the baby than those added to formula. This is a big question and difficult just to tell you a publication which has all the answers. But try one of the big Breastfeeding text books like Lawrence Breastfeeding a Gude for the Medical Profession for starters. Felicity

Dear Milly, Sorry for the delay in responding to you. Here are some references and extracts from Module 1 on IFE that I hope answer your question. Best regards Marie Breastmilk contains all of the nutrients needed by infants in a highly bioavailable form, in balanced proportions and of sufficient quantity to enable healthy growth. Factors in breastmilk aid the digestion and uptake of these nutrients (1). Infants are born with an immature immune system but breastmilk actively and passively protects them from infections [1, 2]. Ingredients in breastmilk bind to and neutralise pathogens [1, 3, 4], attack and kill pathogens [5], deprive pathogens of nutrients [6] and encourage the growth and maturation of the protective lining of the intestine [2]. The digestion of breast milk releases anti-bacterial, anti-viral, anti-protozoal and anti-parasitic factors [7]. Breastmilk promotes the growth of beneficial bacteria in the intestine which out-compete pathogenic bacteria for infection sites and nutrients [8], inhibit the growth of pathogens [9,10] and encourage the growth of the protective mucous layer in the intestine [11]. References: 1. Riordan, J., The biological specificity of breastmilk, in Breastfeeding and Human Lactation, J. Riordan and K.G. Auerbach, Editors. 1999, Jones and Bartlett Publishers: Boston. 2. Goldman, A.S., The immune system of human milk: antimicrobial, antiinflammatory and immunomodulating properties. Pediatric Infectious Disease Journal., 1993. 12(8): p. 664-71. 3. Morrow, A.L., et al., Human-Milk Glycans That Inhibit Pathogen Binding Protect Breast-feeding Infants against Infectious Diarrhea. Journal of Nutrition, 2005. 135(5): p. 1304-1307. 4. Wilson, N.L., et al., Glycoproteomics of Milk: Differences in Sugar Epitopes on Human and Bovine Milk Fat Globule Membranes. J. Proteome Res., 2008. 5. Hanson, L.A., Immunobiology of Human Milk. 2004, Amarillo: Pharmasoft Publishing. 6. Hamosh, M., Protective Function of Proteins and Lipids in Human Milk. Biology of the Neonate, 1998. 74(2): p. 163. 7. Newburg, D.S., Innate Immunity and Human Milk. Journal of Nutrition, 2005. 135(5): p. 1308-1312. 8. Bifidobacterium strains from resident infant human gastrointestinal microflora exert antimicrobial activity 9.1136/gut.47.5.646. Gut, 2000. 47(5): p. 646-652. 10. Gibson, G.R. and X. Wang, Regulatory effects of bifidobacteria on the growth of other colonic bacteria. Journal of Applied Bacteriology., 1994. 77(4): p. 412-20. 11. Bye, N., Protecting the infant through nutrition: are prebiotics the answer? Nutrition Bulletin, 2004. 29(3): p. 213-220.

Iron absorption from breast milk has been found very high (nearly 50%) in an old much quoted study using radioactive isotopes (1). This absorption level is much higher than reported iron absorption from other foods and often lead to the conclusion that iron from breast milk is very well absorbed. However, results of this early study using a rather unreliable method, have not been confirmed by more recent ones, estimating the iron absorption level rather between 10 to 20% (2-4), only marginally better than for infant formulas. As breast milk has a low iron content to start with, it is not a very good source of iron. This has to be put in relation to the very low iron requirements of the young infant (< 6 mo). As a reminder, a child is born with a high Hb level, and during the first few weeks, his Hb goes down, making available large quantities of iron which are stored and can be used for Hb synthesis later. The 2004 FAO WHO report on vitamin and mineral recommended intake does not mention any iron requirement for infants less than 6 mo. The time when the child starts needing iron depends on his/her iron stores at birth. These are related to birth weight and also to a large extent to the time of cord clamping. Delayed blood clamping helps to get good iron stores. Children receiving cow milk often often have mild asymptomatic intestinal blood loss which can lead to anemia and arguably breastfed children often have less anemia than those receiving cow milk (but not those receiving infant formulas), but this is not related to a better iron absorption. In practical terms, the low iron content of breast milk means that iron rich foods should be given to children, even if breastfed, during the complementary feeding period, a time when iron requirements are very high and iron stores available at birth have all been used. 1) Saarinen UM, Siimes MA, Dallman PR. Iron absorption in infants: high bioavailability of breast milk iron as indicated by the extrinsic tag method of iron absorption and by the concentration of serum ferritin. J Pediatr. 1977 Jul;91(1):36-9. 2) Davidsson L, Kastenmayer P, Yuen M, Lönnerdal B, Hurrell RF. Influence of lactoferrin on iron absorption from human milk in infants. Pediatr Res. 1994 Jan;35(1):117-24. 3) Domellöf M, Lönnerdal B, Abrams SA, Hernell O. Iron absorption in breast-fed infants: effects of age, iron status, iron supplements, and complementary foods. Am J Clin Nutr. 2002 Jul;76(1):198-204. 4) Abrams SA, Wen J, Stuff JE. Absorption of calcium, zinc, and iron from breast milk by five- to seven-month-old infants. Pediatr Res. 1997 Mar;41(3):384-90.