Milk is a very special food for mammalian babies. It provides essential nutrients; stimulates development of the gut; promotes the growth of the unique neonate gut flora; and kills everything else. Milk is anti-bacterial, anti-fungal and anti-viral. It is used in fruit orchards as a pruning tool dip to prevent the spread of disease between trees, and it is used as a foot dip after ceremonial walking on hot coals. But is cow's milk healthy for adult humans and is milk compromised by pasteurization and homogenization?
Mother's Milk is FierceMilk as it is transferred from breast to baby is loaded with molecular weapons for the protection of the baby's respiratory and digestive systems. Cells from the mother are transferred along with the milk and quickly spread out on the surface of the mouth and digestive system to patrol for pathogens. The mother's immune system detects potential risks as the baby's mouth contacts the mother's lymphatic system at the breast, and the antibodies that are subsequently produced are transferred into the milk. Enzymes in the milk digest bacterial cell walls and other milk proteins are converted into anti-bacterial peptides in the baby's stomach before ultimately being digested into amino acid nutrients. Many of the fat/lipid nutrients in milk are also anti-bacterial or anti-viral. Most of the carbohydrate in milk is the simple disaccharide lactose that most bacteria can't use for food. The remaining 10% of the carbohydrates are extensions of the lactose to make galacto-oligosaccharides (GOS, a.k.a. bifidus factor) that are toxic to all but the few bacterial species that make up the highly specialized microbial community of the human baby gut flora. (Cow's milk has an entirely different composition, e.g. lacks bifidus factor, and supports a different gut flora.)
Milk is Liquid FatIt is hard to transport fat in water, because it isn't soluble. That is true for blood or milk. We have all heard about good and bad cholesterol, LDL and HDL, and the problems of transporting blood lipids from gut to liver to tissues. Specialized carrier proteins are needed for lipid transport in blood and the same is true for milk. Caseins are the milk proteins that coat droplets of fats that make milk white and then form digestible curds in response to the baby's stomach acid and digestive enzymes. We exploit the natural curd forming response of milk proteins and lipid droplets to form yogurts and cheeses.
Pasteurization and Homogenization Put Milk in the Dairy CaseMilk behaves optimally when immediately transferred from the mother's mammary tissue to the baby's digestive tract. Bacteria that contaminate breast milk are quickly killed by cellular and molecular defenses of the milk itself. Thus, breast milk has a long storage life at room temperature, chilled or frozen. The natural defenses of milk also permit regional milk banks, where donated milk is minimally processed and screened, for subsequent use by hospitals to avoid problems, such as necrotizing colitis, associated with the use of artificial feeding substitutes. Commercial preservation of cow's milk in stores has resulted in attempts to extend the shelf-life by heat treatment (pasteurization) to provide additional protection from microbial contamination and homogenization to prevent curd formation.
Milk is for BabiesSo why isn't milk the perfect food? Part of the reason may come from the highly specialized and essential role of milk for mammals like people. Millions of years of extreme selection pressure have made sure that every woman produces ample milk for all of her babies. Until very recently, if the baby could not successfully nurse, it would die. That made breast milk the perfect food for babies and milk was integral to the development of the baby gut, baby gut flora and baby immune system. But that didn't mean that cow's milk would be a healthy commercial food for human adults.
Milk Processing May Accentuate Casein Amyloid Fiber FormationProteins are made of a long sequence of a thousand amino acids. At each of those thousand positions there is one of twenty different amino acids. Some of the amino acids are hydrophilic and bind to water, whereas other amino acids are hydrophobic and bind only to lipids. Proteins in water fold and unfold in thousands of alternative configurations until the final shape is reached in which there is not enough energy in the molecular vibrations and movements of the water molecules to knock the protein into an alternative shape.
Heating/pasteurization and torturous mixing/homogenization can force milk casein and fats into new configurations that make the proteins stackable into fibers/amyloids. These milk protein fibers may be of interest, because protein fibers are important in many diseases, e.g. type I diabetes, Alzheimer's disease. The problem with amyloids, is that these fibers form a natural repetition of the same amino acid on each of the stacked proteins. This repetitive amino acid, e.g. positively charged lysine or arginine, can provide a binding site for a similarly spaced, oppositely charged molecule, such as heparin, which is involved in dragging molecules from the surface into cells. Beta amyloid fibers with positively charged amino acids in a band along their edges are what kills nerve cells in Alzheimer's disease.
Research has recently demonstrated that milk casein forms amyloid fibers in response to pasteurization and homogenization. It would be interesting to know if these fibers bind to heparin and if these fibers are toxic to intestinal cells.
I have raw cream from grass fed cows in my morning coffee and my three daughters never tasted formula.