A new study shows that soy may protect you from BPA. Here’s what you need to know.
Depending on whom you ask, soy is either toxic sludge or a superfood.
Now, a new study in the Journal of Clinical Endocrinology & Metabolism, showing that soy fights some of the harmful effects of BPA exposure, adds to the evidence that “superfood” may be a more accurate descriptor.
For the study, researchers with the Harvard T.H. Chan School of Public Health looked at 239 women who had undergone at least one in vitro fertilization cycle, and analyzed their conception rates in relation to both their diet and their BPA exposure. (BPA, aka bisphenol A, is a synthetic compound found in many plastic products and household goods that has been linked to infertility and is present in more than 96 percent of Americans’ bodies, according to the Centers for Disease Control and Prevention.) Researchers found that in women who didn’t eat soy, higher BPA levels were associated with decreased chances of embryo implantation and fewer live births. However, in women who routinely ate soy, BPA levels had no effect on IVF success.
While this is the first study to examine the link between BPA and soy in humans, previous animal studies have suggested that soy works by preventing BPA from adding methyl groups to your DNA, explains lead study author Jorge E. Chavarro, associate professor of nutrition and epidemiology at the Harvard T.H. Chan School of Public Health. “In other words, BPA switches on and off certain genes [to inhibit fertility] and soy prevented BPA from doing so.”
Chavarro recommends that women struggling to conceive eat more soy. Women may benefit by eating just one extra serving of soy, such as tofu, tempeh or edamame few days, according to the study’s findings.
But what about if you aren’t trying to grow your family? Is it always so good for you?
The Good, the Bad and the Estrogenic
Much of the debate on soy’s health effects – both good and bad – centers on isoflavones, phytoestrogens that have some similarities with the estrogen that naturally occurs in our bodies.
However, mounting research suggests that soy isoflavones don’t work exactly like estrogen, says registered dietitian nutritionist Sharon Palmer, author of “The Plant-Powered Diet.” For instance, while research from the Memorial Sloan-Kettering Cancer Center suggests that soy may speed up cancer growth in women with pre-diagnosed breast cancer, results from the Shanghai Women’s Health Study reveal that women who ate the most soy during adolescence and early adulthood had nearly a 60 percent lower risk of pre-menopausal breast cancer than did women with the lowest intakes of soy. And in one study of 97,275 California women, those who consumed even a few ounces of soy milk daily were at decreased risk of ovarian cancer. The researchers, from the Stanford University School of Medicine, note that some phytoestrogens actually block estrogen from attaching to cells and stimulating the growth of breast and breast cancer cells.
And in men, eating soy has no effect on testosterone levels, according to research published in Fertility and Sterility. According to the American Cancer Society’s nutritional guidelines, soy foods may help lower the risk and aggressiveness of prostate cancer.
Meanwhile, isoflavones have been credited with reducing the risk of heart disease, osteoporosis and cognitive decline in older adults. Research in Biochemical and Biophysical Research Communications also shows certain soy isoflavones reduce the proliferation of fat cells and may present a new method for combating obesity.
Beyond Isoflavones
The current study on soy and fertility highlights an important point about soy: Its effects don’t begin and end with its estrogenic ways, Chavarro says.
“Even if the isoflavones are removed, you can see some cardiovascular benefits from eating soy, suggesting that something about the protein itself, or the simple act of replacing some meat meals in your diet, can account for some of soy’s benefit on heart health,” says Heather B. Patisaul, an endocrinology and biology researcher at North Carolina State University.
For instance, soy is rich in high-quality protein, fiber, vitamins, minerals and anti-inflammatory compounds. “It’s an excellent plant-based alternative, and it has the best protein and amino acid profile of any plant proteins out there,” Palmer says. “I especially hate to see vegans and vegetarians avoiding soy, as it’s such an important food and it contains an important amino acid called lysine that many other plant proteins lack.”
Eat Soy the Right Way
“If you want to maximize your potential benefits from eating soy, then eat natural, minimally processed sources,” Patisaul says. “That way, you get the full mixture, including the protein, fiber, isoflavones and other ingredients. Tofu, tempeh and edamame are some of the best sources.”
Similarly, it’s worth noting that while these sources (not to mention soy nuts, beans and milk) get the gold-star of approval, experts just don’t know what the overall effects of eating large amounts of isolated soy products, such as soy protein isolate supplements and powders, would be. “It is already well known that eating too much soy can shut down a woman’s menstrual cycle, at least temporarily,” Patisaul says. “For vegetarians this may be a potential concern, but the average person doesn’t eat anywhere near that much.”
So if some soy is good and too much is, well, too much – how much soy should you add to your plate? Palmer notes that one to two servings a day of eating whole or minimally processed soy is generally agreed upon as the safe spot. A serving equals about 1 cup of soymilk or edamame or 1/2 cup of soy meat alternative, tofu or soybeans.
Although, if you currently don’t eat any soy, adding just a bit to your diet, especially in order to sub out meat, can potentially benefit your health, Patisaul says.
Written for Health.USnews.com