Soy Appears to Decrease Risk of Breast Cancer Recurrence, Death

< Dec. 09, 2009 > -- The risk of death and cancer recurrence in women who have had breast cancer may be lowered with regular consumption of a moderate amount of soy foods, according to new research.

Furthermore, the association between soy and a reduced risk of death held true even for women with estrogen receptor-positive cancers and women taking tamoxifen, according to the study published in the Journal of the American Medical Association.

Study author Dr. Xiao Ou Shu, a professor of medicine and a cancer epidemiologist at Vanderbilt University Medical Center in Nashville, Tenn., says, "We found that women with a history of breast cancer who consumed moderate amounts of soy food were doing better in terms of prognosis. They had reduced mortality and reduced recurrence."

Soy's Effect Different than Expected

There has been some concern that soy might increase the risk of breast cancer or worsen the prognosis for women already diagnosed with the disease because soy is a phytoestrogen. That means that it can act like a weak form of estrogen in the body.

However, it appears those concerns may have been unfounded because Dr. Shu and her colleagues found that soy actually reduces the availability of naturally-occurring estrogen by binding to its receptors.

"In our study, we found that soy food has a very similar effect to tamoxifen," says Dr. Shu. Tamoxifen is a drug that blocks the action of estrogen in the body, which can be helpful for treating cancers that are fueled by estrogen.

Study Details

Dr. Shu's study included just over 5,000 Chinese women who had been previously diagnosed with breast cancer between 2002 and 2006. The women were aged 20 to 75, with the majority of women between 40 and 60 at the time of diagnosis.

The researchers collected information on cancer diagnosis and treatment, lifestyle factors (including diet), and disease progression at six months after diagnosis, and then again at 18, 36, and 60 months after diagnosis.

Women who had the highest intake of soy had a 29 percent reduced risk of death and a 32 percent decrease in the risk of cancer recurrence compared to those who ate less than 5.3 grams of soy per day.

According to Dr. Shu, there was a linear response, and the researchers that found the higher the intake, the lower the mortality, up to 11 grams of soy protein taken in daily. She adds that after 11 grams daily, the benefit leveled off but did not decline.

Eleven grams of soy translates to about one-fourth of a cup of tofu each day, says Dr. Shu.

Soy Source Should be Considered

Dr. Shu, along with Dr. Gina Villani, chief of hematology/oncology at The Brooklyn Hospital Center in New York City, say it is important to note that Chinese women tend to get their soy from natural sources, such as tofu, edamame, or unsweetened soy milk, instead of the processed types of soy foods that many Americans eat, such as sweetened, flavored soy milk or soy-based protein bars.

"The take-home lesson is that whole foods are what we need to eat more of," says Dr. Villani. "Try to stay away from the processed stuff. Don't bulk up on soy milk or soy candy bars."

Dr. Shu also points out that Chinese women may be replacing unhealthier food choices, such as red meat, with soy. In an accompanying editorial in the same issue of the journal, experts from the US National Cancer Institute (NCI) noted that the average daily soy intake for people living in China makes up 10 percent or more of their daily protein intake.

Both Drs. Shu and Villani advise against loading up on soy supplements, as these have not been proven to be beneficial, and Dr. Villani says it is unclear if such high levels of soy could cause harm.

And, Dr. Villani adds, "Supplements don't replace food. We haven't even begun to understand the interactions between nutrients in food and the body. Soy as a bean may react different than soy from a candy bar in the body."

"Soy food intake has been shown to reduce the risk of breast cancer, and it may have cardiovascular benefit, so overall, whether or not you have cancer, soy could be very beneficial to you and could become an important component of a healthy diet," says Dr. Shu. "But try to get it in natural sources, not from processed food."

Always consult your physician for more information.

Nutrition to Reduce Cancer Risk

The scientific community is continually studying the role of diet in the development of cancer. Many results are preliminary and more is being learned every day.

Research is discovering that intake of fruits, vegetables, and cereal grains may interfere with the process of developing cancer of the oral cavity, larynx, esophagus, stomach, colon, lung, prostate, and rectum. In addition to reducing the risk of developing cancer, the risk of developing heart disease, hypertension, obesity, diabetes, and other chronic diseases might also be prevented by eating more fruits and vegetables.

There is also evidence that total fat intake of greater than 30 percent of total calories can increase the risk of developing some cancers. This is especially true when total fat intake includes saturated fat and possibly polyunsaturated fat.

The Food Guide Pyramid, Dietary Guidelines for Americans, and 5 A Day for Better Health Campaign are good sources for nutritional information.

Although research studies are inconclusive at this time, preliminary evidence suggests that some components of food may play a role in decreasing the risk of developing cancer, including phytochemicals, antioxidants, and omega-3 fatty acids.

Phytochemicals are chemicals found in plants that protect plants against bacteria, viruses, and fungi. Eating large amounts of brightly colored fruits and vegetables (yellow, orange, red, green, white, blue, purple), whole grains/cereals, and beans containing phytochemicals may decrease the risk of developing certain cancers as well as diabetes, hypertension, and heart disease. The action of phytochemicals varies by color and type of the food. They may act as antioxidants or nutrient protectors, or prevent carcinogens (cancer causing agents) from forming.

Antioxidants are substances that inhibit the oxidation process and act as protective agents. They protect the body from the damaging effects of free radicals (by-products of the body’s normal chemical processes). Free radicals attack healthy cells, which changes their DNA, allowing tumors to grow. Research is underway to investigate the role of antioxidants in decreasing the risk of developing cancer.

Researchers are studying the effects omega-3 fatty acids have on delaying or reducing tumor development in breast and prostate cancer. Since our bodies cannot make omega-3 fatty acids, we must get them from food or supplements.

Always consult your physician for more information.