-Dr. Kathy Johnson, PhD, CMC
There has been much controversy regarding the safety of soy food and products for women that have survived breast cancer. A recent study done by the Journal of the American Medical Association (JAMA) found that women in China who had breast cancer had an associated lower risk of death and breast cancer recurrence when they had a higher intake of soy food.
“Soy foods are rich in isoflavones, a major group of phytoestrogens that have been hypothesized to reduce the risk of breast cancer. However, the estrogen-like effect of isoflavones and the potential interaction between isoflavones and tamoxifen have led to concern about soy food consumption among breast cancer patients,” the authors write in explaining why they pursued this study.
The study analyzed data from the Shanghai Breast Caner Survival Study. It was based off a large population of 5,042 women, all of whom were breast cancer survivors in China. The women were between the ages of 20 and 75 and were diagnosed between March 2002 and April 2006 and followed up through June 2009.
The researchers collected information about the diagnosis, treatment, lifestyle after exposure and disease progression. It was gather approximately 6 months after the diagnosis and reassessed at three follow-up interview conducted at 18, 36 and 60 months after diagnosis.
After 4 years there were 444 deaths and 534 recurrences out of the 5,042 women followed in this study. Patients in the groups with the highest amount of soy protein intake had a 29% lower risk of death during the study and 32% lower risk of reoccurrence compared to the patients with the lowest intake of soy protein.
“The inverse association was evident among women with either estrogen receptor-positive or -negative breast cancer and was present in both users and nonusers of tamoxifen,” the researchers write.
“In summary, in this population-based prospective study, we found that soy food intake is safe and was associated with lower mortality and recurrence among breast cancer patients. “
”The association of soy food intake with mortality and recurrence appears to follow a linear dose-response pattern until soy food intake reached 11 grams/day of soy protein; no additional benefits on mortality and recurrence were observed with higher intakes of soy food. This study suggests that moderate soy food intake is safe and potentially beneficial for women with breast cancer.”
There were several different factors that went into their study such as the differences in the quality, type and quantity of soy food intake between China and the United States. Also, the amount of time the doctors followed up with the women in remission was only 4 years, a short amount of time.
As well, US doctors that there are likely differences in screening rates in China compared with the US and a number of factors make it difficult to compare stage and treatment specific results in China with outcomes in the U.S.
“Even though the findings by Shu et al suggest that consumption of soy foods among breast cancer patients is probably safe, studies in larger cohorts are required to understand the effects of these foods among diverse clinical subgroups of breast cancer patients and survivors.
“In the meantime, clinicians can advise their patients with breast cancer that soy foods are safe to eat and that these foods may offer some protective benefit for long-term health. Moreover, the potential benefits are confined to soy foods, and inferences should not be made about the risks or benefits of soy-containing dietary supplements. Patients with breast cancer can be assured that enjoying a soy latte or indulging in pad thai with tofu causes no harm and, when consumed in plentiful amounts, may reduce risk of disease recurrence.”