Sensitivity Analysis And Publication Bias
Sensitivity analyses showed that no individual study excluded changed the combined RR substantially between soy, soy isoflavones and soy protein and any of the outcomes. The Egger’s or Begg’s did not indicate the presence of publication bias for most associations examined in the current meta-analysis, except for the associations between soy protein intake and risk of overall cancer incidence soy intake and risk of prostate cancer . Furthermore, the trim and fill correction procedures indicated that the pooled RRs were not affected by publication bias .
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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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.
Soya cycle
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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Lower Risk Of Breast Cancer
Research shows that women who consume soy are less likely to get breast cancer. One study found that women averaging one cup of soy milk or about one half cup of tofu daily have a 30% lower risk of developing breast cancer compared with women who eat little or no soy. This may be due in part to protective substances called isoflavones found in soy foods.
In a 2013 meta-analysis that analyzed data from 22 studies, researchers found that, among Asian women, those who consumed the most isoflavones had a 32% lower risk of breast cancer. A protective effect was observed for both pre- and postmenopausal cancers. A 2014 meta-analysis reached similar conclusions. Western women dont typically eat much soy, so its harder to compare between high and low levels of intake. However, eating soy foods during the preteen and teen years, when breast tissue is forming, may be especially protective.
Provides Relief From Osteoporosis
Soymilk is beneficial in providing relief from osteoporosis in postmenopausal women. Osteoporosis is a risk for women in post-menopausal years of age. Often known as brittle bones, loss of calcium contributes to the risk of developing this disease.
Studies have found that an animal protein diet increases urinary excretion of calcium and a soy-based protein diet does not. Since increasingly soymilk is also fortified with calcium, it could be said that soymilk helps in retaining and providing supplements to the body. Natural hormone replacement therapy with soy isoflavones may improve retention of bone mass and density, and thereby reduce the risk of fracture in postmenopausal women.
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Is Soy Safe To Eat After Breast Cancer
New Study Suggests Soy Will Not Increase Risk of Return of Breast Cancer
April 5, 2011 — For years, breast cancer survivors were often counseled to avoid soy foods and supplements because of estrogen-like effects that might theoretically cause breast tumors to grow.
Now, a new study of more than 18,312 women shows that eating soy foods did not increase risk of breast cancer recurrence.
The new findings are being presented at the American Association for Cancer Research 102nd Annual Meeting in Orlando, Fla.
âIf you regularly eat soy, you donât need to worry or avoid it, and women who want to lead a healthy life, can safely include some soy in their diets,â says study researcher Xiao Oh Shu, MD, PhD, a professor of medicine at Vanderbilt Epidemiology Center of Vanderbilt University Medical Center in Nashville, Tenn.
In addition to the isoflavones which may act like estrogens in the body, âsoy has many anticancer properties, antioxidants, nutrients, micronutrients, or vitamins that may contribute to its beneficial effect on health,â Shu says.
Shu and colleagues analyzed data from four large studies of women with a history of breast cancer diagnosed between ages 20 and 83. Soy intake was assessed using questionnaires in all of these studies. The study only looked at soy foods, not supplements.
Favor Whole Soy Foods
While foods made using whole soybeans like edamame, tofu, and soy milk have health benefits, highly processed soy products likely do not. Some food companies have separated protein from whole soybeans and used it to make soy protein isolate. Theyve packed this isolate into shakes and turned it into meat substitutes. Unfortunately, soy protein isolate may not be healthy. In fact, its been shown to increase the amount of insulin-like growth factor in the blood, just like cows milk. Insulin-like growth factor can promote cancer growth. So stick to simple soy products like tofu, tempeh, edamame, soy milk, or miso. These foods may help protect against cancer while providing health benefits.
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Myth: Eat Soy To Protect Against Breast Cancer
While eating a moderate amount of soy is fine, itâs too soon to suggest eating more to protect your breasts.
âThe results are promising, but thereâs still not enough information,â Meyers says. Experts now believe that soy isoflavones may actually block estrogen from attaching to breast cancer cells instead of spurring growth like once thought.
Meyers notes that many of the hallmark studies are done in Asian countries, where people grow up eating soy in its traditional forms. âThat may influence the way their body processes soy,â she says. âWe need to look at if having soy later in life has the same effect.â
More research also needs to be done on how much soy you get at different ages. âSoy may have more of an impact on a postmenopausal woman whoâs not producing as much estrogen as a healthy 20-year-old,â Millstine says.
Soy And Breast Cancer: Is There A Connection
Medically Reviewed By: Wendy Y. Chen, MD, MPH
Could adding soy milk to your coffee or substituting tofu for meat increase your risk of breast cancer? The research is conflicting, but our breast cancer doctor, Wendy Chen, MD, MPH, is here to help us cut through the noise.
one of the most common questions I get from breast cancer survivors, says Chen, a breast oncologist with the Susan F. Smith Center for Womens Cancers at Dana-Farber.
While laboratory studies on soy compounds in isolation have sparked questions about a possible connection, studies of breast cancer patients in China and Japan have not shown any increased breast cancer risk resulting from soy consumption.
There is a biological basis for this line of inquiry.
Soy has what are called phytoestrogens, Chen says. These are plant-based estrogens. If you look at certain compounds in isolation, some of them have been shown in lab studies to increase cancer cell growth. However, that has never been shown in people.
The most extensive population studies on this issue were conducted in China. The Shanghai Womens Health Study surveyed more than 70,000 Chinese women about their health and food intake, including soy. Soy consumption is exponentially higher in China than in the United States. Many Chinese are lactose intolerant, and so they begin drinking soy milk in childhood. In addition, other forms of soy, such as tofu and edamame, are part of the traditional Chinese diet.
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Can Eating Soy Increase Your Risk Of Breast Cancer
Some types of cancer, such as hormone receptor-positive breast cancer, use human estrogen to grow and spread. Because of this, some people may worry that eating the phytoestrogens found in soy could increase estrogen in their bodies and encourage breast cancer growth.
However, no studies in people have shown a link between eating soy and having breast cancer. Studies done in the laboratory have shown that isoflavone enhanced the growth of breast cancer cells and promoted breast cancer tumors in rats. However, these studies were not done in people, and laboratory studies are not used to make dietary recommendations for people. Researchers have also discovered that rats metabolize soy differently than humans do.
Scientific data suggests that consuming soy foods as part of a diet with lots of other plants is a great way for breast cancer survivors to care for their bodies. However, if you’re not comfortable including soy foods, survivors can have a perfectly healthy diet that does not include soy foods. Julie LG Lanford, MPH, RD, CSO, LDN, registered dietitian and nutritionist with 15 years of experience working in oncology nutrition
Does Eating Soy Impact Your Risk Of Breast Cancer
Soybeans are high in plant protein, fiber and other nutrients. On the other hand, soy has been targeted as a food to avoid when it comes to hormone-sensitive cancers like breast cancer. So, when it comes to breast cancer risk, is soy helpful or harmful?
There is a lot of confusion around soy but, the truth is, soybeans are a healthy food and can be a great alternative to animal-based protein, says Lynne Groeger, M.S., R.D., C.S.O., registered dietitian specializing in oncology nutrition with Riverside Cancer Care Center.
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Straight Talk About Soy
The Takeaway: Soy is a unique food that is widely studied for its estrogenic and anti-estrogenic effects on the body. Studies may seem to present conflicting conclusions about soy, but this is largely due to the wide variation in how soy is studied. Results of recent population studies suggest that soy has either a beneficial or neutral effect on various health conditions. Soy is a nutrient-dense source of protein that can safely be consumed several times a week, and probably more often, and is likely to provide health benefitsespecially when eaten as an alternative to red and processed meat.
Soy is exalted as a health food by some, with claims of taming hot flashes, warding off osteoporosis, and protecting against hormonal cancers like breast and prostate.
At the same time, soy is shunned by others for fear that it may cause breast cancer, thyroid problems, and dementia, though these claims have not been substantiated.
Whether published in a popular press article or a well-designed clinical study, some debate about soy remains. As a species within the legume family, nutrition scientists often label soy as a food with potential for significant health benefits. However, due to contrary research that suggests possible negative effects of soy in certain situations, there has been a hesitancy to wholeheartedly promote soy.
Thus, there are many factors that make it difficult to construct blanket statements about the health effects of soy.
| Unfermented soy foods |
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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Intake Of Soy Soy Isoflavones And Soy Protein And Risk Of Cancer Incidence And Mortality
- 1The First Affiliated Hospital, Xi’an Jiaotong University Health Science Center, Xi’an, China
- 2Key Laboratory of Shaanxi Province for Craniofacial Precision Medicine Research, College of Stomatology, Xi’an Jiaotong University, Xi’an, China
- 3School of Public Health, Xi’an Jiaotong University Health Science Center, Xi’an, China
- 4Key Laboratory for Disease Prevention and Control and Health Promotion of Shaanxi Province, Xi’an, China
- 5Key Laboratory of Environment and Genes Related to Diseases , Ministry of Education of China, Xi’an, China
Background and Aims: Associations between soy intake and risk of cancer have been evaluated in prospective observational studies with inconsistent results. Whether the potential anticancer effects offered by soy were attributed to soy isoflavones and soy protein still needs to be elucidated. This study aimed to comprehensively quantify the association of soy, soy isoflavones and soy protein intake with risk of cancer incidence and cancer mortality by conducting a meta-analysis of all available studies.
Higher intake of soy and soy isoflavones were inversely associated with risk of cancer incidence, which suggested that the beneficial role of soy against cancer might be primarily attributed to soy isoflavones. These findings support recommendations to include soy as part of a healthy dietary pattern for the prevention of cancer.
Soy May Be Okay For Breast Cancer Survivors
Prospective studies show no increased risk of recurrence.
At one time, soy seemed to be just the ticket for women: heart-healthy, good for bones, and helpful for hot flashes. And then there was the low rate of breast cancer in soy-consuming countries. But as so often with “miracle foods,” closer study has dampened some of the enthusiasm.
Early research indicated that soy protein could lower LDL cholesterol, but later studies were so unimpressive that the American Heart Association asked that food companies no longer be allowed to label soy products as helpful in preventing heart disease. It’s still unclear whether soy does much for bones or hot flashes. And although some studies suggest that it may protect against breast cancer, other research has found that isoflavones can spur the growth of breast cancer cells in test tubes and animals. There’s also some concern that soy’s estrogenic activity may interfere with tamoxifen, a drug used to prevent recurrence in women with estrogen-sensitive breast cancer. As a result, some clinicians advise patients with breast cancer to limit their consumption of soy or avoid it altogether.
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Lower Risk Of Recurrence
What about women who have been diagnosed with breast cancer? Researchers found that women diagnosed with estrogen-negative breast cancer who ate the most soy isoflavones had a 21% lower risk of dying from cancer compared with those who ate the least.
The Womens Healthy Eating and Living Study also showed that soy may help protect breast cancer survivors. Researchers found that women who ate the most soy cut their risk of cancer coming back or cancer death in half. Another study followed 5,042 women previously diagnosed with breast cancer for four years. Women who regularly consumed soy products like soy milk, tofu, or edamame came out ahead. They were about a third less likely to have their cancer come back, and 29% less likely to die from cancer compared with women who ate little soy. Numerous other studies confirm these findings. Women who avoid soy get no advantage, while women who consume soy are less likely to have their cancer return.
Soy Is Most Protective For One Kind Of Breast Cancer
The apparent protective power of soy depended on what kind of breast cancer a woman had. For women with hormone receptor positive breast cancer, including those taking hormonal adjuvant therapies, eating more soy was neutral. There was no harm but no benefit in terms of mortality.
Women whose breast cancer was hormone receptor negative, however, really benefited from soy. These are women who are not candidates for hormonal adjuvant therapies such as tamoxifen. For these women, who dont benefit from these medications that help prevent recurrence, eating more soy is one step they can take to improve their odds. And since the study also found that women who started eating more soy after diagnosis benefited, its clear that while a lifelong soy habit is healthy, its never too late to start.
The findings echoed the results of earlier research published in TheAmerican Journal of Clinical Nutrition that women who ate more soy-based foods after diagnosis were 25% less likely to have recurring tumors than women who ate little or no soy after diagnosis. So this is the second major study in the US demonstrating that women with breast cancer who eat soy tend to do betternot worse.
What about isoflavone supplements? Unfortunately, this study didnt cover them, so no conclusions can be drawn about whether they are beneficial or safe.
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