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About one in four women will eventually suffer from fibroids, most commonly manifesting as excessively heavy periods and pain or pressure. Why might you feel pressure? Because you may be carrying around 26 pounds of tumors in your uterus. Fibroids are the most common reason women get hysterectomies—having their uterus removed completely, a major surgery associated with disability and death. But, all surgery carries risk. The chances of dying within a month of surgery may only be about one in 1,200, which makes it among our safest surgeries—safer than getting your gallbladder removed, for example. But, of course, you lose the ability to bear children, and these surgeries cost billions of dollars a year. Yet, “[d]espite the high prevalence, significant [pain and suffering], and huge economic…impact…, relatively little is understood” about the cause and disease process that lead to fibroid tumors.

Avoiding atomic bomb blasts whenever you can is probably a good idea in terms of decreasing fibroids risk. But, what about more easily modifiable risk factors? Well, alcohol consumption is associated with increased risk—particularly beer. And, whenever you hear that, whenever you hear beer specifically, you think of the hormonal effects specific to beer—specifically the powerful phytoestrogen found in hops. Well, if that phytoestrogen is increasing fibroids risk, what about the phytoestrogens in soy?

Well, this was looked at in the Black Women’s Health Study. Fibroids are two to three times more prevalent among African-American women. So, they thought maybe dairy intake might be “contribut[ing] to the disparity,” given their higher levels of lactose intolerance. And, indeed, dairy consumption was associated with reduced risk. They figured it was the calcium content, or maybe the vitamin D. But perhaps the women were drinking soy milk instead, and that was increasing their risk? No. “Soy intake was [found to be] unrelated.” Same finding in a group of predominantly white women, though they did note a protective association with the amount of lignans flowing through their bodies. Lignans are another class of phytoestrogens found predominantly in flax seeds, but also throughout the plant kingdom. Hard to make any generalizations about the soy phytoestrogens, though, as soy consumption was rather low across the board. This research was done in Washington state.

If you go to Japan, where they have the highest per capita soy consumption in the world, you could get a bigger spread of intakes. The researchers had “previously found that soy…intake was inversely associated with the risk of hysterectomy”—meaning women who ate more soy had lower hysterectomy rates, suggesting a potentially protective effect of soy against uterine fibroids, since that’s the main reason women have their uterus removed. This would be consistent with in vitro studies that found that the main soy phytoestrogen seemed to inhibit fibroid tissue proliferation in a petri dish. But, when they specifically looked, “[t]here was no evidence of” a link to soy at all, protective or otherwise. The same was found in one study out of China. Fruit and vegetable intake was associated with significantly lower risk of fibroids, but soy food consumption was not.

But, a second study out of China, published the same year, found a significant association between soy milk intake and fibroids. That’s consistent with the three alarming case reports of women with symptomatic fibroids reporting “an unusually high intake of soy milk,” or “regularly consuming excessive amounts of soy,” or “extremely high intake[s] of soy…everyday” for decades. It’s hard to take these cases seriously when nowhere do they actually say how much they were consuming. The only quantitative mention was 40 grams of isoflavones, which roughly translates to 400 gallons of soy milk every day. That would be excessive, but also impossible.

The only way to know for sure is to put it to the test. Not just a population study or anecdotal reports, but randomize women to two years of soy phytoestrogens—the amount found in three to five cups of soy milk a day—and “no significant” effect on the frequency or growth of fibroids was found.

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