Most commercial cow’s milk—including most organic milk—goes through a few stages of processing before it reaches the store shelf. It’s usually pasteurized in order to kill any pathogenic bacteria it may contain. You can read more about the pros and cons of unpasteurized, or “raw” milk, in my special two-part series on that subject.
Most commercially-sold milk is also fortified with vitamins A and D, in an effort to ensure adequate intake of these nutrients in the general population. Commercial milk is also usually homogenized—a mechanical process that breaks the fat globules into smaller droplets so that they stay suspended in the milk rather than separating out and floating to the top of the jug. Before milk is homogenized, some of the fat may be skimmed off to reduce the amount of fat in the end-product.
What is homogenized milk?
Homogenization was invented around the turn of the 20th century and quickly became the industry standard because people preferred the convenience of milk that didn’t have to be vigorously shaken to distribute the fat every time you wanted to use it. These days, of course, we tend to see food processing as something that reduces the nutritive value of foods. And some have suggested that homogenization might have a negative impact on how the milk affects your body.
In fact, it’s getting more common to find milk that’s pasteurized but not homogenized. Sometimes it’s labeled “cream-line.” Let’s take a closer look at whether or not unhomogenized milk might be a better choice.
Is homogenized milk bad for your heart?
When you homogenize milk, you not only change the size of the fat globules, you also rearrange the fat and protein molecules—which could alter how they act in the human body. In the 1970s, Kurt Oster proposed the hypothesis that homogenized milk might increase your risk of heart disease. Specifically, he theorized that xanthine oxidase, a compound that’s created when milk is homogenized, might be absorbed intact into the blood stream, where it would deplete other protective compounds called plasmalogens and result in the formation of plaques and heart disease.
Researchers spent the next decade or so testing various aspects of Dr. Oster’s rather ornate hypothesis. Ultimately, research failed to validate any part of it. Xanthine oxidase does not appear to be abosrbed into the blood stream from the digestive tract. Drinking homogenized milk does not increase blood levels of xanthine oxidase nor does this compound appear to have any effect on plasmalogen levels.
Purveyors of nonhomogenized milk often claim that it is more digestible. But in fact, studies suggest the opposite: homogenization increases the digestibility of milk.
More recently, some research has suggested that the smaller fat globules in homogenized milk might be more likely to raise LDL (or “bad”) cholesterol levels, compared with the larger fat globules in unhomogenized milk, cream, or cheese. However, the consumption of dairy fat (in any form) is not linked with an increase in heart disease. Indeed, several studies have shown a slight inverse association, with greater dairy consumption linked to slightly lower risk of heart disease.
Does homogenization make milk more digestible?
Purveyors of nonhomogenized milk often claim that it is more digestible. But in fact, studies suggest the opposite: homogenization increases the digestibility of milk—particularly in people with diseases that impair their ability to digest fats. Because the protein and fats are broken down into smaller particles, there is more surface area for enzymes to work on and this leads to more efficient digestion. If, however, you are lactose intolerant or allergic to milk, homogenization isn’t going to make milk any more or less tolerable for you.
Some people who are neither allergic nor lactose intolerant still feel that they tolerate unhomogenized milk better than homogenized. However, when researchers did double-blind tests, they found that subjects were just as likely to report symptoms with unhomogenized as with homogenized milk, suggesting that the perceived difference is mostly a placebo effect.
Does homogenization affect vitamin D or calcium absorption?
I’ve also seen claims that your body is less able to absorb calcium or vitamin D from homogenized milk. I have been unable to find a single study, paper, or reference to support the idea that homogenization has a negative impact on either your vitamin D or your calcium status. Rather, I found evidence that consuming homogenized milk that’s been fortified with vitamin D leads (as you might expect) to improved vitamin D and calcium status.
In fact, homogenized milk is more likely to be fortified with vitamin D, which obviously makes it a better source of the nutrient.
That said, as I’ve discussed in previous articles, although cow’s milk is a good source of calcium and vitamin D, it is certainly not the only source for either nutrient, nor is dairy milk essential to a healthy diet.
Homogenized milk is more likely to be fortified with vitamin D, which obviously makes it a better source of the nutrient.
Homogenization vs. pasteurization
Finally, I want to be sure we don’t confuse homogenization with pasteurization, because the two have nothing to do with one another. Pasteurization has to do with killing bacteria; homogenization has to do with emulsifying fat—and milk can be either, neither, or both. Organic certification is also completely unrelated to whether the milk is homogenized or pasteurized.
Here’s the bottom line on homogenization: If you like the idea of eating closer to nature, unhomogenized milk is definitely less processed. You may also enjoy the flavor or texture (or perhaps the nostalgia) of milk where the cream floats to the top. If, on the other hand, you prefer the flavor, texture, or convenience of homogenized milk, there doesn’t appear to be any danger in choosing that instead.