Certain gut bacteria can supercharge the benefits of soy foods, resulting in even more bone protection, better control of menopausal symptoms, and lower prostate cancer risk, but how can we foster the growth of these good bacteria? 

Menopause is characterized by a decrease in estrogen, which triggers the uncomfortable symptoms of hot flushes [also known as hot flashes], night sweats, sleep disturbances, and vaginal dryness. Among these menopausal symptoms, hot flushes are reported by many women to be the most bothersome.” You may be familiar with my summary of the available evidence on the role of soy phytoestrogens to help alleviate those symptoms presented in my earlier video Soy Foods and Menopause. I discuss the latest meta-analysis in my more recent video, How to Convert Into an Equol Producer. Although the balance of evidence points to the benefits of soy, the individual study results are all over the place. Yes, some studies show 20, 30, even 40 percent better than control, but some showed no effect, as you can see at 0:38 in my video. 

This is something that’s been noted by professional societies like the American College of Obstetricians and Gynecologists. Indeed, these supplements may work, but the evidence is inconsistent. This may be partly because the supplements used were extracted from different parts of the soybean. Imight be better if, instead of supplements, soy foods were used. The dosing would be about two servings of traditional soy foods a day—for example, two cups of soy milk. In fact, that is what you see older women in Japan doingand they have some of the lowest reported rates of hot flashes in the world. Nevertheless, even the studies on soy foods, as opposed to supplements, have reported conflicting results. Why all the inconsistency? It may have to do with our gut bacteria. 

People who eat foods made from soybeans, which have health-promoting isoflavones, tend to have lower rates of a variety of chronic diseases, such as “cardiovascular disease, osteoporosis, and some cancers such as breast, prostate, and colon cancers,” so can we garner this protection by eating more soy foods? 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, but not all individuals can make this conversion. Why not? Because not all individuals have the specific types of good bacteria in their gut that do it. There are two types of people in the world: equol producers and equol nonproducers, depending on their gut flora. 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, you may remember a study I covered previously about how soymilk appears to prevent bone loss in the spines of postmenopausal women, which I show at 2:32 in my videoWell, if you split those women into equol producers and equol nonproducers, you’ll find that soy did work in equol nonproducers, but it seemed to work even better in the women whose gut bacteria can 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, as you can see at 2:55 in my video. Some studies suggest equol-producing men may get less prostate cancer. If that’s the case, perhaps we should examine the possibility of improving the intestinal environment to enable equol production. Only a minority of the Western adult population can produce equol, though nearly every other animal species appears to be able to produce it without any problem. In fact, it got its name because it was first discovered in equinesInterestingly, horses produce equol during the summer, but not the winter, because summertime is when their gut bacteria have access to the phytoestrogens in clover. That was our first clue that equol was made from plants. 

“This then begs the important question, i.e., can we take someone who does not make equol and convert them to an equolproducer? Certainly, it is possible to do the reverse; excessive use of antibiotics, which wipe out intestinal flora, is likely to do this” by getting rid of 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, though, so how about dietary alteration? About half of Japanese and Korean individuals can produce equol, but only as low as one in seven Americans canCould it be because more soy is eaten in Asia? 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. A month of soy isoflavone supplement exposure didn’t seem to convert equol-nonproducers into producers, thoughAfter just two weeks of drinking three glasses of soy milk a day, however, three of six women were converted into equol-producers. As you can see at 4:45 in my video, for example, woman started out hardly making any equol at all. After two weeks of drinking soy milk, though, she got nice equol spikes when the researchers had her drink some more, but it didn’t work for all women. And, when researchers tried the same experiment in men, nothing happened. Back to the drawing board. 

Is there any group of Westerners with high equol production rates from whom we may be able to get a clue? Vegetarians have among the highest equol production rates ever recorded and are more than four times as likely to be equol producers as their non-vegetarian counterparts. Why? Researchers don’t think it’s because of the soy, given the conflicting soy data, but could it be because they’re eating more prebiotics, such as fiber? Or, maybe dietary fat intake decreases the capacity of gut flora to make equol, or perhaps it has something to do with cholesterol intake. Analyzing the diets of equol producers, it seems they are more likely to be eating greater amounts of carbohydrates, plant protein, and fiber. 

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. 


The balance of evidence finds that soy is beneficial for alleviating menopausal symptoms.
Eating foods made from soybeans may lower rates of myriad chronic diseases, including heart disease, osteoporosis, and breast, prostate, and colon cancers.
Certain gut bacteria can convert the isoflavones in soy into equol, which is potentially even more beneficial, but not everyone has the specific types of bacteria to do so.
This difference in gut flora may help explain the variations in soy benefits found in studies.
Those whose gut bacteria are able to produce equol may experience fewer menopausal symptoms and less prostate cancer, for example.
Only a minority of Western adults can produce equol, though virtually all other animal species seem to be able to do so. 

Equol is made from plants. 

Vegetarians have among the highest rates of equol production and are more than four times as likely to produce equol than non-vegetarians.

What was that about safely helping to control hot flashes? Check out my video Soy Phytoestrogens for Menopause Hot Flashes. 

Plant-based eating has a variety of healthy effects on our good gut bacteria. See, for example: 

Microbiome: The Inside Story

Microbiome: We Are What They Eat 

Flashback Friday: Prebiotics – Tending Our Inner Garden 

What’s Your Gut Microbiome Enterotype? 

How to Change Your Enterotype 

How to Develop a Healthy Gut Ecosystem

How to Become a Fecal Transplant Super Donor 

How to Reduce Your TMAO Levels 

Flashback Friday: Gut Dysbiosis – Starving Our Microbial Self 

Is Fiber an Effective Anti-Inflammatory?

Benefits of Flax Seeds for Inflammation 

Benefit of Dates for Colon Health

In health, 

Michael Greger, M.D. 

PS: If you haven’t yet, you can subscribe to my free videos here and watch my live presentations: 

2019: Evidence-Based Weight Loss 

2016: How Not To Die: The Role of Diet in Preventing, Arresting, and Reversing Our Top 15 Killers 

2015: Food as Medicine: Preventing and Treating the Most Dreaded Diseases with Diet 

2014: From Table to Able: Combating Disabling Diseases with Food 

2013: More Than an Apple a Day 

2012: Uprooting the Leading Causes of Death