The Side Effects of the Hormones in Milk

Below is an approximation of this video’s audio content. To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring, watch the above video.

We’ve known for decades that women who eat meat have higher levels of estrogen in their blood. Compared to nonvegetarians, vegetarian women were found to have 45 percent lower levels of the most potent human estrogen. This may help explain the lower incidence of breast cancer among those eating more plant-based. Even semi-vegetarians who eat less meat than omnivorous women may have significantly lower estrogen levels. Why? Perhaps because vegetarian women excrete two to three times more estrogens in their feces than do their meat-eating counterparts. And why is that? Because the average fecal output of vegetarians can be twice as high. Look at those heavyweight Vs compared to the featherweight Os. The thought is that because vegetarians eat the amount of fiber closer to that which is natural for our species, those relying more on plants have an increased fecal output, which helps pull excess estrogen out of the system.

It may also have something to do with the hormones present in animal products. For example, the higher average blood concentrations of estrogen associated with high dairy consumption would be consistent with milk as a major source of estrogens in the human diet. The reason we’re concerned is that the increased consumption of animal-derived foods may have adverse effects on the development of hormone-dependent cancers. Among dietary risk factors, these investigators were most concerned about milk and dairy products, because the milk we drink today is produced by pregnant cows with markedly elevated levels of both estrogen and progesterone. The genetic manipulation of dairy cows enables them to lactate throughout almost their entire pregnancies, which is why commercial cow’s milk contains large amounts of estrogens and progesterone these days. That may be why milk-drinkers have five times the rates of having twins compared to vegans—that’s how much of an effect dairy may have on our hormones.

But we don’t really know how much the hormones in dairy affects our hormones until we put it to the test. Researchers looked to see what happens when men and prepubescent children, who both would normally have low estrogen levels, chug a quart (950 ml) of cow’s milk in under 10 minutes. This is what happened to the men. Within an hour of drinking the milk, their levels of the estrogen estrone went up, and progesterone and testosterone significantly dropped within 60 minutes.

It’s funny, there are men who don’t want to drink soy milk because of the phytoestrogens— even though soy phytoestrogen normally does not have feminizing effects on men—yet they’re perfectly willing to drink cow’s milk, which has actual estrogen estrogens in it!

In children, researchers saw the same thing—the levels of estrogens flowing through their body within an hour of drinking milk more than tripled: estrone, the potent estrogen estradiol, the pregnancy estrogen estriol, and a progesterone metabolite. And half the kids couldn’t even finish the whole quart (950 ml) of milk.

There’s also another sex steroid hormone present in cow’s milk called 5alpha-pregnenedione (5alpha-P) that is a direct precursor to a type of testosterone that may not only drive acne but also promote prostate cancer.

Now, we’d like to see controlled clinical studies, but the problem is there is no control. Dairy without the offending estrogen does not exist. Even organic milk from cows who aren’t injected with extra hormones has growth hormones in it, because biologically, that’s the whole point of milk—to put a couple of hundred pounds on a baby calf.

The problem with humans drinking cow hormones is there’s no natural feedback loop. For our own hormones, if we have too much estrogen or something, our brain dampens it down. But our own protective feedback system is bypassed when our system is invaded by these dihydrotestosterone precursors in dairy products. See, the human endocrine system, our hormonal system, didn’t evolve under the influence of ingested dairy and other external hormones and growth factors, and we’re just not equipped to cope with such a quote-unquote “sneak attack.”

In summary, evidence suggests that consumption of dairy-sourced hormones, which aren’t subject to any innate feedback inhibition, may be the source of the steroid sex hormones that drive acne and at least prostate cancer. This is perhaps the most promising unifying hypothesis—or theory—to explain the cause of diverse conditions that blemish, scar, shorten, or take the lives of millions.

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Motion graphics by Avo Media

• acne
• breast cancer
• cancer
• dairy
• estrogen
• fiber
• hormones
• meat
• milk
• organic foods
• phytoestrogens
• Plant-Based Diets
• prostate cancer
• soy milk
• vegetarians