Edamame is having a moment. The trendy dish of steamed and seasoned soybeans is popping up on menus as a tasty appetizer, but it’s just one way to prepare and enjoy soybeans, a staple crop that’s a major source of protein for people in many parts of the world. Soybeans can also be made into tofu, a common meat replacement that some vegetarians and vegans rely on. Recently, soy milk has become so popular, it’s now widely available as a dairy alternative in most coffee shops. Further, miso, tempeh and soy powder are also common foods that originate from soybeans. Breastcancer.org reports that “soybeans are the most widely used, least expensive and least caloric way to get large amounts of protein.”
Soybeans are hot these days, with some advocates even suggesting they’re a superfood. Yet there remains some concern about whether soybeans can elevate risk for breast cancer. This stems from some cellular data and studies conducted in animals showing that compounds in soy products could have an estrogen-mimicking effect. But then other studies have shown that soy products might actually have an anti-cancer effect, an idea bolstered by epidemiological data indicating a much lower incidence of breast cancer in Asian populations, which tend to consume a lot more soy products than people following a more Western diet. And thus developed a debate: Can soy products contribute to the development of breast cancer or can consuming foods made from soybeans actually help protect you from the disease?
[See: A Tour of Mammographic Screenings During Your Life.]
Marian L. Neuhouser, head of the cancer prevention program in the public health sciences division of Fred Hutchinson Cancer Research Center in Seattle, says “some of the controversy or worry about soy consumption started with in vitro or cell data,” where scientists tested the estrogenic effects of isoflavones on cancer cells in the laboratory. Isoflavones are a type of phytochemical (i.e. compound found in plants) that can mimic the effects of estrogen, which is a prime driver of most breast cancers.
“Isoflavones have a structural similarity to estrogen,” Neuhouser explains. “They travel around the body in the blood, and they have a weak estrogenic effect, meaning they can bind to the estrogen receptor [on breast cancer cells] and perhaps have a similar effect as estrogen itself,” causing the cancer cells to grow. “About 75 percent of breast cancers are what we call estrogen-receptive positive, which means they use estrogen to grow. The other 25 percent are ER-negative, which means they grow and proliferate independent of estrogen. That’s where the link comes from, because [isoflavones have] this weak estrogenic effect that could perhaps mimic estrogen. There’s this thought that it could fuel breast cancer growth.”
Dr. Sagar Sardesai, assistant professor of medicine at the Stefanie Spielman Comprehensive Breast Center at The Ohio State University Wexner Medical Center. notes that “isoflavones are not hormones themselves, but when these substances are in the body, they can turn on the estrogen receptor, the same way the circulating estrogen can stimulate the estrogen receptor on breast cells.” In breast cancer, these receptor cells become overactive, leading to tumor growth. So because isoflavones stimulate this same pathway, logically it follows that they could encourage cancer growth. Studies have been far from conclusive on this causal connection, but because of these concerns, Sardesai says the breast cancer soy connection is “such a hot topic, at least two-thirds of my patients ask whether they can eat soy.”
In addition to soy-based foods, isoflavone compounds can be found in canned goods and preservatives, and because soybeans are often used in animal feed, they can get into some of the meat we eat, Neuhouser says. “In the U.S., even though soy is widely dispersed throughout the food supply, we still have a much, much lower consumption than in Asian countries where they’re eating a lot of soy,” and also tend to have a much lower incidence of breast cancer. “The isoflavone intake [in the U.S.] on average is less than 5 milligrams per day, so it’s really pretty low.” (By comparision, a 2009 analysis of data collected as part of the Shanghai Women’s Health Study, which had more than 73,000 participants, found consumption of isoflavones ranged from 11.23 to 54.97 milligrams per day.) In addition, she notes that “most of the data in U.S. cohorts has no association of soy consumption either with breast cancer risk or survival,” but some recent studies have indicated that consuming higher amounts of soy products could actually be “associated with reduced risk and reduced breast cancer mortality.”
[See: The 10 Best Diets for Healthy Eating.]
In this discussion, it’s important to note that the bulk of the data has been derived from laboratory studies done on cells or in animals, not in actual human beings. And many of the studies used very high levels of these compounds that would be tough to consume in dietary form, says Dr. Gertraud Maskarinec, a preventive medicine physician and nutritional epidemiologist at the University of Hawaii Cancer Center. The idea that soy should be avoided to reduce risk of breast cancer is “based on animal studies with very, very high concentrations of isoflavones in a way that you can never eat as a human,” she says. And for some people, the protein that soy can provide may be a better, lower-calorie option than meat. “I am completely convinced [soy is] a good food, and eating it instead of steak is no problem for breast cancer. Replacing your steak with a piece of tofu on occasion is neither here nor there,” she says, with moderation and controlling obesity being the really important points.
Sardesai agrees that soy can be part of a healthy, balanced diet even among breast cancer patients and survivors. “For a woman who has a moderate- to low-intake of soy, I definitely do not ask her to stop that,” and he says that the amount of soy you’ll be exposed to if you eat canned foods or drink a cup of soy milk each day are not a concern.
That said, Sardesai, Maskarinec and Neuhouser all warn against using soy supplements. Neuhouser says “we have very little data on soy supplements, so some of these over the-counter products — they’re usually marketed as hot flash remedies or post-menopausal remedies that have pretty high amounts of isoflavones — we don’t have data about whether they’re beneficial or harmful. But soy from foods, I think we can say it’s safe for women. It’s a good source of protein, and a good-quality protein. I think we’re coming to the conclusion that soy is safe for women to consume.”
Sardesai agrees. “In my patients who have been diagnosed, I often tell them ‘don’t take soy supplements.’ Given this debate and given this conflicting evidence both in cell lines and mouse models and some prospective small human studies, I don’t feel comfortable asking women to take a large amount of soy. But if you’re drinking a cup of soy milk a day, that’s perfectly OK. I think anywhere between 5 to 10 grams of soy per day is not going to affect you negatively based on the evidence we have so far,” he says.”
“As long as one thinks about food, it’s OK,” Maskarinec says. “The minute they take out ingredients of the food, such as the isoflavones, and put it in pills and injections,” then it’s smart to be concerned, “but not about a piece of tofu.” She says high-protein drinks and other foods that contain “lots of soy protein, I don’t consider those foods,” so talk with your doctor about whether or not to include such products in your diet.
[See: What Not to Say to a Breast Cancer Patient.]
If you’re dealing with a breast cancer diagnosis, you should discuss diet with your doctor anyway, but particularly if you use tofu or other soy products as your primary source of protein, Sardesai says. “I wouldn’t stop them from doing that because I still don’t have evidence that it impacts negatively with regard to breast cancer risk or metastases. But I would discuss the data with my patients and raise caution that it may not be a bad idea to change to some other form of protein.”
And for women who have no personal history of breast cancer, he says eating soy doesn’t pose a concern. “There’s very little data” regarding whether consuming soy elevates risk in people at average risk of developing the disease. So, if that describes you, enjoying a splash of soy milk in your daily cup of coffee and that edamame appetizer at your favorite restaurant appear to be completely safe.
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Does Eating Soy Products Increase or Lower My Risk of Breast Cancer? originally appeared on usnews.com
