With the first sale of homogenized milk occurring in the state of Connecticut in 1919, U.S. consumers have become accustomed to milk in a physical state very different from its natural one. Natural milk is an oil-in-water emulsion, and like all emulsions, milk is unstable, and if left to sit over time, will find its fat (oil) portion rising to the top of its water portion and forming a cream layer. The formation of a cream layer at the top of the milk would occur in all of our store-bought milk if the milk were not homogenized. But milk can be passed through a valve, under high pressure, so that its fat droplets will be broken apart into much smaller droplets only 0.2 to 2 microns in size. Unlike the larger, natural fat droplets found in milk, these pressure-created micro-droplets will stay dispersed in the milk.
Beginning in the 1960's and continuing through the 1980's, an M.D. named Kurt Oster published a series of articles questioning the health safety of homogenized milk. He hypothesized a connection between homogenization and the development of heart disease. According to Oster's hypothesis, an enzyme called xanthine oxidase (XO) was naturally associated with the fat globules in milk. Homogenization was theorized to trap XO in the new micro-droplets and prevent this enzyme from being metabolized in the digestive tract. Oster was convinced that because of homogenization, unmetabolized XO was being absorbed from the digestive tract up into the blood stream where it could trigger immune reactions and cause damage to blood vessel walls. The result was described as plaque formation—the very same plaque formation that gives rise to atherosclerosis in many U.S. adults.
Research studies have yet to conclusively prove, or disprove, Oster's hypothesis. There continues to be strong interest in XO, however, and its relationship to heart problems. However, the potential contribution of homogenization to these problems remains a research hypothesis at this point in time rather than a research conclusion. In fact, very little attention has been given to this hypothesis over the past ten years in peer-reviewed research journals.
Non-homogenized milks are available in the U.S. We support their consumption, even though we have not seen research that confirms the connection between homogenization and risk of heart disease, or the mechanism of XO damage. But homogenization is a processing step that takes us away from the natural form of whole milk. It's carried out for convenience and texture, not for nourishment or safety.
It's possible to produce non-fat milk by letting whole milk naturally separate into non-fat milk and cream—without any homogenization whatsoever. It's also possible to purchase goat's milk, which often requires no homogenization because the fat droplets in goat's milk are smaller to begin with and remain better dispersed in the liquid portion of the milk. In the absence of better research, it's impossible for us to take a stand against the consumption of homogenized milk for health reasons. But we recognize the more natural composition of non-homogenized milk, and we support its availability and consumption.
Enig, MD. (2003). Milk Homogenization & Heart Disease. Wise Traditions in FOod, Farming, and the Healing Arts, Weston A. Price Foundation, Summer Quarter.
Oster, K., Oster, J., and Ross, D. "Immune Response to Bovine Xanthine Oxidase in Atherosclerotic Patients." American Laboratory, August, 1974, 41-47
Oster, K., and Ross, D. "The Presence of Ectopic Xanthine Oxidase in Atherosclerotic Plaques and Myocardial Tissues." Proceedings of the Society for Experimental Biology and Medicine, 1973.