Should Cancer Patients Avoid Soy
Do soy foods increase your cancer risk? April marks National Soy Foods Month, so let’s explore that question.
According to historical documents and archaeological finds, soybeans were first cultivated sometime in the 11th century BC in the eastern half of northern China, and soy has remained an important part of Asian diets ever since. Soy was first introduced to the United States in the mid-1700s. These days, soy sometimes gets a bad rap, but it can be part of a healthy pattern of eating.
Reading Health Behaviors In Different Countries Correctly
Science tries to avoid correlating behaviors with risk factors too quickly. And its that very reason extensive research must first be done to take all factors into consideration.
Consider any correlation between soy and breast cancer world-wide. Rates of breast cancer in general are much higher in the United States than in many Asian countries for example, where soy products are a major diet staple, Dr. Roesch says.
Those countries also typically feature an overall lower-fat diet and differences in birthrates, both of which affect cancer rates.
One possible reason breast cancer has been on the rise lately in these countries may be due to adoption of a Western diet and lifestyle, which may include higher intake of saturated fats and not specifically the consumption of soy.
Best Bet Is Moderation
The study didnt address the question of whether soy does or doesnt prevent breast cancer, or whether soy would have any effect on women who dont have breast cancer or have premalignant lesions.
The researchers general recommendation is not to avoid soy, but like most everything else in the modern diet to consume it in moderation. If you currently have early-stage breast cancer, dont eat soy in large amounts. If youve had breast cancer, you can eat soy, but in moderation, says Dr. Bromberg.
It seems reasonable to advise at this present state of the knowledge that women dont overconsume soy, adds Dr. Shike. When it comes to nutrition, variety is important, and so is moderation.
Read more about this study in HealthDay.
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What Human Studies Show
A number of long-term studies involving human populations have shown that eating soy foods does not increase the risk of breast cancer. On the contrary: Studies show that diets rich in soy may actually help to protect you from developing breast cancer.
A 2020 study that tracked the soy consumption of over 300,000 women in China found that moderate soy consumption did not raise the risk of breast cancer for women in the study. Women in the study who reported eating higher amounts of soy products experienced a lower risk of breast cancer.
A 2020 meta-analysis evaluated the results of 18 separate studies. After evaluating the results of these studies, researchers concluded that higher amounts of soy in the diet lowered the breast cancer risk for women. The protective effect was highest for women who had not yet reached menopause.
American Cancer Society say soy foods are safe and healthy for people to eat. They caution, however, that more research needs to be done to see whether taking isoflavone supplements is equally safe, since these supplements may have higher concentrations of isoflavones than there are in soy foods.
A Small But Significant Effect
Study participants had recently undergone breast biopsies and were diagnosed with stage 1 or 2 breast cancer and scheduled to have a mastectomy or lumpectomy two to three weeks later. During the time between their diagnosis and surgery, the women were randomized to receive either soy protein or a placebo as part of the study.
From the original pool of participants, those in the soy group who had high levels of genistein, a component of soy, were evaluated along with patients in the control group who did not take soy to look for signs of changes in gene expression or molecular changes in their tumors.
High levels of genistein are an indirect way of knowing whether you had actually consumed high levels of soy, meaning those participants consumed the food, says Dr. Bromberg.
Not everyone who took the soy had high levels of genistein and changes in gene expression were seen only in patients who did experience an increase. Only 20 percent of those patients who took the soy had really high levels of the genistein metabolite, she says, adding that the reasons behind that disparity arent clear, and that theres no way to predict who would have this reaction after consuming soy.
Of the women with high genistein levels, a few of them experienced changes in a specified set of genes that are established to be involved in breast cancer cell growth, death, or some aspect of breast cancer pathology, Dr. Bromberg adds.
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Myth: All Types Of Soy Have The Same Effect On The Body
Your body may process the natural soy in tofu, miso, and soy milk differently than the kind thatâs added to processed foods.
The soy protein isolate found in supplements, protein powders, and meat substitutes is usually stripped of nutrients, such as fiber.
âItâs also a more concentrated form of soy,â Millstine says. âSo youâre much more likely to get a high dose if youâre having protein shakes and soy hot dogs than if youâre eating edamame.â
Researchers arenât certain how large amounts of soy affect breast cancer risk. In one early study, soy supplements were shown to âswitch onâ genes that encourage cancer growth in women with early-stage breast cancer.
Experts recommend sticking with a moderate amount, or about one to two servings, of whole soy a day. One serving includes:
- Half a cup of cooked edamame
- 1 cup of soy milk
- 1 ounce of soy nuts
- 3 ounces of tofu
The Questions About Soy And Breast Cancer
Before launching into the controversy about soy and breast cancer, it’s important to point out that this is about more than one question. Many of you have heard that soy may lower the risk of breast cancer, but that breast cancer cells grown in a dish grow more rapidly if fed soy. What is that all about? Some of the separate questions include:
- Can soy intake lower the risk of developing breast cancer? If so, is there a window of time in which it may accomplish this, or does the effect last throughout life?
- Is it safe for those with breast cancer to eat soy, or will it make breast cancer grow faster or increase recurrence?
- Are soy supplements safe for those at risk of breast cancer or who already have breast cancer?
- How may soy interact with the medications commonly used to treat breast cancer?
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Soy Intake While On Aromatase Inhibitors Or Tamoxifen
While soy may help relieve your hot flashes, researchers caution postmenopausal women against having too high a dose of soy, particularly in the form of supplements that contain high amounts of soy isoflavones. And if you’ve had estrogen-sensitive breast cancer, and are taking a selective estrogen receptor modulator, such as tamoxifen, or an aromatase inhibitors, such as exemestane, it’s a good idea to refrain from soy. The soy isoflavone genistein may counteract estrogen suppressorsand that would make your post-treatment medication less effective.
After you’ve completed a full course of estrogen suppressors you can start including soy in your diet again, in modest amounts. But first, talk with your oncologist. If you still want the benefits of isoflavones, try dining on legumes, whole grains, and nuts. On the other hand, a good reason to avoid soy altogether is if you know that you’re allergic to it. You should also skip soy if you have a thyroid disorder or goiter.
Differences In How Soy Is Processed
First, mice process the soy differently than humans do. To understand how, a little background is necessary. Soy contains several kinds of phytoestrogens . Phytoestrogens are plant-based substances that act like estrogen in the body.
According to the American Cancer Society , certain types of breast cancer have been traced to increased estrogen in the body. Thats what gave researchers cause for concern about soy and breast cancer. However, in humans, phytoestrogens turn into genistein and daidzein, two isoflavones that are very different from and much weaker than human estrogen.
In fact, soy has been proven to in tissues. In tissues with breast cancer cells, estrogen stimulates the multiplication of cancer cells. When soy blocks this stronger form of estrogen, it is playing an active role in reducing the risk of breast cancer.
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Is It Safe For Survivors
Studies of pre- and post-menopausal women suggest soy isoflavones may have a protective effect against breast cancer. Population studies indicate that soy consumption in survivors of breast cancer may be linked to decreased recurrence and greater overall survival. A 2017 study looked at more than 6,200 American and Canadian women with breast cancer. These women filled out surveys about what they ate and other lifestyle habits. Those women who ate the highest amounts of isoflavones had a 21% lower risk of having died from any cause, compared to the women who ate the lowest amount of isoflavones.
Fermented Soy Will Heal Your Gut
Toss the fart-y processed tofu and veggie burgers, and stick to fermented varieties like tempeh, miso, and natto, which are easier to digest. Smith explains that “Fermented soy is generally thought of as ‘better’ than regular soy because the fermenting process reduces ‘anti-nutrients,’ such as phytic acid and sapoinin, and also because isoflavones are thought to be more available for our bodies to use in this form.” Not to mention fermented foods are also a great source of gut-healthy probiotics which can promote healthy digestion. Natto, in particular, is touted for its unique benefits due to its high levels of vitamin K2which is important for cardiovascular and bone healthas well as the presence of nattokinase, an enzyme found in the fermented food which has been shown to dissolve blood clots.
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Soy Foods Are More Than Just Tofu And Soy Sauce
Soy foods are made from soybeansa crop that, until the 1980s, has been used in America primarily as livestock feed, but has been a part of the Asian diet for many generations. Soy is available as edamame , tofu, soy milk, soy powder and flour, miso paste, tempeh, oil, and textured vegetable protein . Soy shows up in many meat analog productsmeatless meatballs, “burger” style crumbles, and even bacon-like strips and chicken-shaped nuggets.
Higher Concentrations Of Isoflavones In Mouse Studies
Because of the differences in how soy isoflavones are metabolized in mice and humans, the mice in these were exposed to much higher concentrations of isoflavones than the amounts human beings typically eat. Researchers have concluded that the higher concentrations mean the outcomes are likely to be different for the two species.
When researchers conducted similar soy , whose biology is much closer to human biology, they found no increased risk of breast cancer among the primates who consumed soy.
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Does Soy Lower The Risk Of Breast Cancer
Although there are not enough data to know whether soy may help protect against breast cancer, many studies suggest that it does.3-4 However, it seems the benefit only comes with a pattern of intake that is seen in most Asian countries, where women begin eating soy early life and eat it in amounts many times greater than typically seen in the U.S.4 In Japan, for example, soy intake ranges from 25 mg to around 50 mg per day. In the U.S., intake ranges from less than 1 mg to 3 mg per day.5
Results from an analysis that combined findings from multiple studies in Asian populations found that women who ate high amounts of soy had a 25 percent lower risk of breast cancer compared to those who ate lower amounts.6 When the same analyses were done in studies of U.S. and other Western populations, there was no link between soy and breast cancer risk.6
Research On Soy And Disease
Learn more about the research on soy and specific diseases or other conditions:
Soy protein took center stage after research showed that it might lower levels of harmful cholesterol. A 1995 meta-analysis of 38 controlled clinical trials showed that eating approximately 50 grams of soy protein a day in place of animal protein reduced harmful LDL cholesterol by 12.9 percent. Such reductions, if sustained over time, could mean a greater than 20% lower risk of heart attack, stroke, or other forms of cardiovascular disease. In response to this finding, in 1999 the Food and Drug Administration allowed companies to claim that diets low in saturated fat and cholesterol that also contain soy may reduce the risk of heart disease.
However, a number of studies since have tempered that finding. According to a comprehensive update of soy research by the nutrition committee of the American Heart Association published in 2000, eating 50 grams of soy per day lowered LDL by only about 3%. In October 2017, after review of additional scientific studies since the health claim was authorized, the FDA proposed a rule to revoke the claim because numerous studies presented inconsistent findings on the relationship between soy protein and heart disease. Some of these inconsistencies may have resulted because soy was compared with a variety of alternative foods.
Another prospective study followed 1,954 American women who were breast cancer survivors for six years. Key highlights of the study:
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Checking For Risk Of Breast Cancer Recurrence
After an average of nine years after their breast cancer diagnosis, women who consumed the highest amount of soy, or more than 23 milligrams of soy per day, had a 9% lower risk of dying from any cause and a 15% reduced risk for breastcancer recurrence, compared to women who consumed 0.48 milligrams of soy per day or less.
These results were not considered statistically significant and therefore may be due to chance.
According to Shu, 23 milligrams per day of soy consumed is the equivalent of one glass of soy milk or a half cup of tofu.
Leif Ellisen, MD, PhD, of the Gillette Center for Breast Cancer at the Massachusetts General Hospital Cancer Center in Boston, says women often ask him whether soy is safe after breast cancer.
âThere are a lot of health benefits in soy, but there has been some theoretical concern that soy has molecules that resemble estrogen which may increase risk of breast cancer recurrence,â he says.
But ârather than any negative effect, this study suggested a benefit for these patients in terms of overall health and breast cancer recurrence,â he says. âThis is quite reassuring for women who were concerned that they might have to eliminate healthy soy foods from their diets.â
One Reason There Isnt A More Definitive Answer Is Because Isoflavone Either Acts Like Oestrogen In The Body Or Its Opposite
One reason there isnt a more definitive answer is because isoflavone either acts like oestrogen in the body, or its opposite. When we eat soya, isoflavone either binds to the alpha oestrogen receptor in the body, which stimulates a tumours growth rate, or the beta receptor, which decreases growth rate and induces apoptosis.
Isoflavone prefers to bind to beta receptors, says Bruce Trock, professor of epidemiology and oncology at Johns Hopkins School of Medicine in Maryland in the US. That makes it more likely to reduce potential cancer risk.
The impact of soya on breast cancer risk may depend on when we start eating it.
Most studies on Asian populations included women who have eaten it since early childhood and were probably also exposed to it in the uterus, says Trock, compared to Western studies involving women who mostly didnt eat soya until later in life.
Starting to consume soya products at an earlier age may make soya more beneficial
Giving soya to animals at the equivalent of middle age doesnt seem to reduce risk or growth rate of tumours, he says.
But if researchers feed mice prior to puberty, then expose them to carcinogens, they get fewer and smaller tumours than if you dont give them soya.
Meanwhile, clinical and population data shows daily soya intake can halve the frequency and severity of hot flashes even when the placebo affect is taken into consideration, says Mindy Kurzer, professor of nutrition at the University of Minnesota.
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The Humble Soybean Is One Of The Most Controversial Foods On The Planet
Accused one minute for causing breast growth in boys and men, celebrated as a healthy alternative for those with lactose intolerance, the next. For breast cancer patients, the question is whether soy cures breast cancer, or causes it.
The science is split: there are just as many pro-soy studies as there are those that seek to demonize it. Nevertheless, soy continues to be a popular area for continued research.
Both sides of the argument focus on an element of soybeans called isoflavones .
In vitro studies showed that certain amounts of isoflavones can inhibit the growth of many cancer cells, including breast cancer. Amounts less than this sweet spot, however, have the opposite effect – the isoflavones begin mimicking estrogen and stimulate cancer cell growth .
Similarly, soy consumption has been both suggested as capable of reducing hot flushes and vaginal dryness in postmenopausal women, and of interfering with the efficacy of Tamoxifen. . In vitro studies showed that soy effectively blocked Tamoxifen from working, whereas animal studies showed that combining soy isoflavones with Tamoxifen was 33% more effective than tamoxifen alone. .
Researchers were first prompted to look deeper into soy, after a study, carried out in 1990, found that soy protein provided a protective effect to rats that had been chemically induced with breast cancer . Human-based studies began and from 1991 onwards, results seemed to support the benefits of soy .
So, should I eat it, or not?