Theories abound as to which foods help or hurt in preventing cancer or easing its effects on the body. Researchers at Memorial Sloan Kettering have recently uncovered evidence that addresses one often-discussed food in many diets: soy.
In a controlled, randomized study of women with newly diagnosed, early-stage breast cancer, MSK scientists found that, in a subset of participants, adding a moderate amount of soy to the diet led to an increase in the expression of genes associated with cancer growth.
In a small portion of the women in the study, “there was evidence that genes that promote proliferation were overexpressed,” says gastroenterologist, internist, and nutritionist Moshe Shike, a coauthor of the study and leading researcher in the field of diet and nutrition.
The study was not long enough to address the question of whether these changes in gene expression would lead to enhanced tumor growth. “Although the genes were being expressed, it is not clear that this will translate into actual tumor growth,” says physician-scientist Jacqueline Bromberg, a coauthor of the study. “But the concern is that there may be the potential.”
The findings were published in the September 4 issue of the Journal of the National Cancer Institute.
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 aren’t clear, and that there’s 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.Back to top
Amount of Soy Could Be Normal for Some Diets
Though the levels of soy given to study participants was significant — about 51.6 grams, or the equivalent of about four cups of soy milk, per day — people who eat soy regularly could reasonably consume that amount throughout the course of a day, particularly vegetarians, those who don’t consume dairy, or people from Asian countries, says Dr. Bromberg.
“We’re not talking about 20 times more soy. We’re talking about something that a person could eat,” she adds.Back to top
Best Bet Is Moderation
The study didn’t address the question of whether soy does or doesn’t prevent breast cancer, or whether soy would have any effect on women who don’t 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, don’t eat soy in large amounts. If you’ve 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 don’t overconsume soy,” adds Dr. Shike. “When it comes to nutrition, variety is important, and so is moderation.”
Read more about this study in HealthDay.Back to top