I’m, somewhat regretfully, part of a number of huge vegan groups on Facebook. That means I see in my newsfeed people arguing about soy nearly every day.
Is soy pumping us full of estrogen? Is soy making endometriosis worse? Is soy promoting breast cancer?
The answer to all of these questions, as far as science has explored (and it’s explored quite a lot in this arena) is a resounding no.
Science indicates that soy is not only not bad for your body, but that it is a nutritional powerhouse. It’s a disease fighter.
And this is not just in comparison with cows milk—which is, if you’re so concerned about man boobs, full of hormones. Of course milks that come from humans and other animals have hormones! There are hormones present in milk even from dairy cows not given bovine growth hormone. That is simply what happens when you take the milk from a recently pregnant mammal. Hormones abound. They’re supposed to be there.
Scientific studies regarding health effects of soy:
Below, find links to large scientific studies. Emphasis via bold text is added by me.
“Soyfoods have been intensely researched, primarily because they provide such abundant amounts of isoflavones. Isoflavones are classified as both plant estrogens and selective estrogen receptor modulators. Evidence suggests that these soybean constituents are protective against a number of chronic diseases, but they are not without controversy. In fact, because soyfoods contain such large amounts of isoflavones, concerns have arisen that these foods may cause untoward effects in some individuals. There is particular interest in understanding the effects of isoflavones in young people. Relatively few studies involving children have been conducted, and many of those that have are small in size. While the data are limited, evidence suggests that soy does not exert adverse hormonal effects in children or affect pubertal development. On the other hand, there is intriguing evidence indicating that when soy is consumed during childhood and/or adolescence, risk of developing breast cancer is markedly reduced. Relatively few children are allergic to soy protein, and most of those who initially are outgrow their soy allergy by 10 years of age. The totality of the available evidence indicates that soyfoods can be healthful additions to the diets of children, but more research is required to allow definitive conclusions to be made.”
“Recent data from Asia and North America indicate that soy foods may decrease the risk of breast cancer and improve the results of treatment in patients with breast cancer. Studying soy foods and isoflavones promises to be an exceptionally fertile area for a wide range of cancer researchers.”
Comprehensive evaluation of the role of soy and isoflavone supplementation in humans and animals over the past two decades
“Soy and soy‐based foods are considered healthy, particularly in many Asia–Pacific countries, where soy products have long been consumed. Soy and soy‐related products have been found to help prevent the occurrence of cardiovascular diseases and certain types of cancer, such as breast and prostate cancer. These products can also have antioxidative effects that alleviate hot flashes during menopause and bone loss. These biological and therapeutic functions are primarily due to the isoflavones derived from soy, whose structure is similar to the structure of 17‐β‐oestradiol. Despite the many health benefits for humans and animals, the application of isoflavones remains controversial because of their anti‐oestrogenic properties. We focused on general information regarding isoflavones, as well as their structure, function, and application. We summarized evidence showing that dietary or supplemental isoflavones exert protective effects on the health of humans and animals. Based on the literature, we conclude that soy foods and isoflavones may be effective and safe; however, more high‐quality trials are needed to fully substantiate their potential use.”
“Higher levels of urinary genistein and daidzein were associated with decreased risk of advanced endometriosis (P for trend = 0.01 and 0.06, respectively) but not early endometriosis. For advanced endometriosis, the adjusted odds ratio for the highest quartile group was 0.21 (95% confidence interval = 0.06-0.76) for genistein and 0.29 (0.08-1.03) for daidzein, when compared with the lowest group. Inverse associations were also noted between urinary isoflavones and the severity of endometriosis (P for trend = 0.01 for genistein and 0.07 for daidzein). For advanced endometriosis, ESR2 gene RsaI polymorphism appeared to modify the effects of genistein (P for interaction = 0.03).
^^ I don’t have endometriosis, but somebody on the New Vegan Support Facebook group kept on insisting (with a Youtube video as evidence, OF COURSE) that soy made endometriosis way worse. So I looked into it. Turns out the opposite is true. Lol.
“Soyfoods have long been recognized as sources of high-quality protein and healthful fat, but over the past 25 years these foods have been rigorously investigated for their role in chronic disease prevention and treatment. There is evidence, for example, that they reduce risk of coronary heart disease and breast and prostate cancer. In addition, soy alleviates hot flashes and may favorably affect renal function, alleviate depressive symptoms and improve skin health. Much of the focus on soyfoods is because they are uniquely-rich sources of isoflavones. Isoflavones are classified as both phytoestrogens and selective estrogen receptor modulators. Despite the many proposed benefits, the presence of isoflavones has led to concerns that soy may exert untoward effects in some individuals. However, these concerns are based primarily on animal studies, whereas the human research supports the safety and benefits of soyfoods. In support of safety is the recent conclusion of the European Food Safety Authority that isoflavones do not adversely affect the breast, thyroid or uterus of postmenopausal women. This review covers each of the major research areas involving soy focusing primarily on the clinical and epidemiologic research. Background information on Asian soy intake, isoflavones, and nutrient content is also provided.”
But what about my GAINS???!!!?!1?
There’s less of a consensus here. In a (admittedly quite small; just 27 people) study conducted in 2004, whey protein bars didn’t appear to build muscle any more efficiently than soy protein bars. Though, interestingly, soy products seem to offer antioxidative benefits neither the whey group nor the control group experienced.
Still, there are other studies that indicate dairy milk is better than soy milk at promoting muscle protein synthesis (or MPS). One study says MPS was 18 percent greater after the consumption of whey on a rest day than after the consumption of soy. When consumed after exercise on an active day, MPS was 31 percent greater with whey consumption than with soy. To me it looks like this is due to the speed at which the proteins can be accessed by the body. When looking at whey and soy were both way better at promoting MPS than casein was.
So, IDK, it seems like whey protein may promote muscle growth better than soy, but the effects are not huge. Even if they were, I don’t think my #gainz are more important than cows’ well-being so………………..yeah.
In conclusion: don’t be afraid of soy. Drink that soy milk. It’s simply the best plant-milk option, nutritionally.
Someday soon I’ll write about my favorite high-protein, low-carb products. They’re almost all processed (beans, lentils, etc. are amazing but they are not low-carb) and many of them use soy protein. I eat them because I am not afraid of them. I’m not afraid of them because science has told me not to be.