Milk has long been a critical food source for humans and other mammals. Human milk is highly complex and contains over 100,000 unique biological components, which play a major role in nourishment and disease resistance in babies. Although not all benefits of these components have been fully researched or discovered yet, the following lists important elements of breast milk:

• Immunoglobulins: protective proteins that bind to and help destroy harmful, invading organisms such as bacteria and viruses. Various types of immunoglobulins are found in human milk with the highest concentration found in colostrum, the milk that is only available from the breast the first three to five days of the baby's life. However, immunoglobulin levels, particularly sIgA, remain elevated for a prolonged period of time postpartum.

• Lactoferrin: an iron-binding protein that limits the availability of iron to bacteria in the intestines, as well as enabling certain healthy bacteria to thrive. It has a direct antibiotic effect on potentially harmful bacteria such as Staphylococci and E. coli. It is found in the highest concentrations in colostrum, but persists throughout the entire first year.

• Lysozyme: a powerful digestive enzyme that is found in breast milk at a level 50 times higher than in any formula. Lysozyme destroys harmful bacteria and ultimately influences the delicate balance of bacteria that inhabit the intestinal tract.

• Bifidus Factor: helpful bacteria that can inhibit the growth of disease-causing bacteria and parasites. Breast milk-fed infants have a level of Lactobacillus that is typically 10 times greater than that of formula-fed infants.

• DHA & ARA: part of a group of molecules known as omega fatty acids. DHA (docosahexaenoic acid) is a major building block in the gray matter of the brain and in the retina of the eye. DHA accumulates in the brain over the first two years of life. ARA (arachidonic acid) is found throughout the body and works in conjunction with DHA to support the visual and mental developments of infants. Significantly different amounts of these molecules have been found in the brains and retinas of breast-fed versus formula-fed infants.

• Long-chain Sugars: Human milk is rich in certain types of sugars called oligosaccharides, which appear to affect the delicate composition of bacteria in the baby's gut. Oligosaccharides block the adherence of harmful organisms to epithelial cells (membranous tissue that covers most internal and external surfaces of the body and its organs), helping to prevent infections. These molecules may be one reason why breastfed babies have different gut bacteria than non-breastfed babies.