WHAT IS HOMOGENISED MILK?

What is homogenization and does it detract from the healthfulness of milk?

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; if left to sit over time, its oil (fat) portion will rise to the top of its water portion and form 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.

The process of homogenization, where milk is passed through a valve under high pressure, breaks apart milk's fat 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, creating the more "cohesive" texture we are used to in 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 and 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. He theorized that homogenization trapped XO in the new micro-droplets and prevented 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 into the bloodstream 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 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. But the contribution of homogenization to these problems is still a research hypothesis and not a research conclusion.

For those who are looking for alternatives to homogenized milk, nonhomogenized cow's milk is becoming increasingly available in the U.S. Additionally, goat's milk may be of interest since it often requires no homogenization because its fat droplets are smaller to begin with and remain better dispersed in the liquid portion of the milk. I support the consumption of these nonhomogenized forms of milk, even though I have not seen research that confirms the connection between homogenization and risk of heart disease, or the mechanism of XO damage.

In the absence of better research, it's impossible for me to take a stand against the consumption of homogenized milk for health reasons. Yet, I recognize the more natural composition of nonhomogenized milk, and I support its availability and consumption since homogenization is a processing step that takes us away from the natural form of whole milk. It's one that's carried out for convenience and texture, not for nourishment or safety.