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“Menopause is characterized by a decrease in estrogen, which triggers the uncomfortable symptoms of hot flushes, night sweats, sleep disturbances, and vaginal dryness. Among these menopausal symptoms, hot flushes [also known as hot flashes] are reported by many women to be the most bothersome.” I already summarized the available evidence on the role of soy phytoestrogens to help alleviate those symptoms. Here’s the latest meta-analysis. Although the balance of evidence point to soy benefits, the individual study results are all over the place. Yes, some studies show 20, 30, even 40% better than control, but some showed no effect.

This is something that’s been noted by the professional societies, like the American College of OB/GYNs. Yes, these supplements may work, but the evidence is so inconsistent. This may be partly because the supplements used were extracted from different parts of the soybean. Maybe it would be better if they just used soy foods rather than supplements. The dosing would be about “two servings of traditional soyfoods” a day—like two cups of soy milk, which is what you see older women in Japan doing, who have some of the lowest reported rates of hot flashes in the world. But, even the studies on soy foods, as opposed to supplements, have had “conflicting results.” Why all the inconsistency? It may have to do with our gut bacteria.

People who eat foods made from soybeans, which have these “health-promoting isoflavones,” tend to have lower rates of a variety of chronic diseases. So, we can garner this protection by eating more soy foods, right? Well, it may be a little “more complicated” than that. There are certain gut bacteria that can convert isoflavones in soy into a potentially even more beneficial compound, called equol. Not all individuals can make this conversion, though, because not all individuals have the specific types of good bacteria in their gut that do it. So, there’s two types of people in the world: “equol producers” and “equol nonproducers”—depending on their gut flora. And so, this may help account for the variations in health benefits we see in clinical studies. It may help explain why some people seem to benefit from soy more than others.

For example, in the study I covered before, about how soy milk appears to prevent bone loss in the spines of postmenopausal women, if you split the women into equol producers and nonproducers, soy did work in non-equol producers, but seemed to work even better in the women whose gut bacteria is able to take the soy to the next level.

The more equol Japanese women make from the soy they eat, the fewer menopausal symptoms they may have. Some studies suggest equol-producing men may get less prostate cancer. If that’s the case, maybe we should look into improving the intestinal environment to enable equol production. Only a minority “of the Western adult population” is able to produce equol, though almost every other animal species appears to produce it; no problem.

In fact, that’s how it got its name. It’s named equol because it was first discovered in horses. But, interestingly, horses during the summer, not winter—because that’s when their gut bacteria had access to the phytoestrogens in clover. That was our first clue equol was made from plants. If you’re not Mr. Ed, though, “can [you] take someone who [doesn’t] make equol and convert them [in]to an equol-producer? Certainly, [you can] do the reverse; excessive use of antibiotics” can wipe out your good bugs. But how can you acquire the right good bugs? Suggested strategies include dietary alteration or probiotics.

The standard probiotic regimens don’t seem to help; so, how about dietary alteration? Well, about half of Japanese and Korean individuals can produce equol, but only as low as one in seven Americans. Maybe it’s because more soy is eaten in Asia? I mean, that would make sense—if you eat a lot of soy, you may foster the growth of bacteria in your gut that can digest soy. But, a month of soy isoflavone supplement exposure didn’t seem to convert nonproducers into producers. But, just two weeks of drinking three glasses of soy milk a day was able to convert three of six women into producers. For example, this woman started out not making any at all, or maybe a little bump between hours 50 and 60, but after two weeks of drinking soy milk, when they had her drink some more, she had nice equol spikes.

It didn’t work for all women, though. And, when they tried the same experiment in men, nothing happened. Hmm, back to the drawing board. Is there any group of Westerners that have high equol production rates that may offer a clue? Vegetarians have among the highest equol production rates ever recorded—more than four times as “likely to be…equol producers as their nonvegetarian counterparts.” The question is, why? They don’t think it’s because of the soy, given the conflicting soy data. Maybe it’s because they’re eating more prebiotics, like fiber?

Or, maybe “dietary fat intake decreases the capacity of gut…flora to [make] equol.” Or, maybe it has something to do with cholesterol intake? Analyzing the diets of equol producers, they do seem more likely to be eating more carbs, plant protein, and fiber. But, researchers have tried giving people fiber supplements along with soy, but that didn’t seem to work. Whatever it is about those eating plant-based diets, they may soon be the only remaining majority equol producers, as Asian populations continue to Westernize their diets.

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