Soy Consumption: Safe and Possibly Beneficial for Breast Cancer Survivors

Key Takeaways:

  • Increased consumption of soy may not only be safe but could aid in reducing the risk of mortality in breast cancer survivors.
  • Women diagnosed with breast cancer who had a high intake of soy during the study experienced a lower mortality rate and decreased recurrence of cancer.
  • The concern over soy consumption is due to its estrogen-like compounds, known as isoflavones; however, the new study challenges this concern, showing positive correlation between higher soy intake and reduced death risk.
  • The study also showed a strong benefit for women who did not have hormone-receptor positive cancers, with 50% reduced risk of dying from any cause.
  • High soy dietary intake may play a protective role against breast cancer death by displacing estrogen from its preferred site on the cancer cell, keeping its effects under control.

Controversies surrounding the implications of soy for breast cancer patients have been ongoing for years. It now appears that an increased soy diet may not only be harmless for breast cancer survivors, but instrumental in reducing the risk of mortality.

The Influence of Soy on Mortality Rates

Current research, encompassing more than 6,200 breast cancer survivors, found that those who consumed the highest amount of soy experienced a lower mortality rate throughout the almost 10-year follow-up period. Dr. Fang Fang Zhang, the leader of the study and an assistant professor of epidemiology at the Friedman School of Nutrition Science and Policy in a renowned university, stated that there were no adverse effects detected for women diagnosed with breast cancer who consumed soy in terms of mortality.

Zhang cites, “Overall, an elevated level of soy consumption is linked to a 21 percent reduction in the risk of death compared to women who include soy in their diet less often.”

The Controversy Over Soy

Alerts regarding soy’s ‘risk/benefit’ profile stemmed from the presence of estrogen-like compounds known as isoflavones in the food. Experts say this is crucial because higher estrogen levels can stimulate the growth of cells in hormone-receptor positive breast cancers, which is the most prevalent tumor type.

The outcome of this new study, according to medical oncology professor Dr. Omer Kucuk, should conclusively settle the soy controversy. The results of the study, echoing those of a previous one, show a positive correlation between higher soy intake and reduced odds of breast cancer recurrence. “When you have decreased recurrence, you have decreased mortality,” noted Kucuk.

Kucuk confidently adds, “I think now we can assert that women with breast cancer should not worry about consuming tofu, edamame, miso soup and other soy products, including soy milk.”

Study Observations and Discoveries

The recent study involved participants enrolled in a Breast Cancer Family Registry and had an average age of 52 years at the beginning. Throughout the study, over 1,200 of the participants passed away. The diets of all the women were tracked, some of which were monitored even before their diagnosis of breast cancer.

The researchers discovered an association between higher soy intake and better survival post a breast cancer diagnosis, although the study was not designed to establish cause-and-effect.
Interestingly, a strong benefit was observed for women who did not have hormone-receptor positive cancers – the type that’s sensitive to estrogen. These women had a 50% reduced risk of dying from any cause during the follow-up.

A considerable advantage from high soy intake was also apparent for women who had never undergone hormone therapy for breast cancer treatment – they had a 32% reduced risk of death during the follow-up period.
According to the researchers, women in the ‘low-soy’ group consumed less than 0.3 milligrams (mg) of soy isoflavones daily, while those in the highest group consumed 1.5 mg or more. The median intake was found to be 1.8 mg of soy isoflavones daily, which Zhang explained, is equivalent to about half to one full serving of soy foods, such as soy beans or tofu, per week.

The Protective Role of Soy

The experts could only conjecture why soy might be protective against breast cancer death. Zhang explained that the plant-based estrogen, once attached to the cell surface, makes it less probable for estrogen to attach to the same cell. Essentially, the soy isoflavone dislodges the estrogen from its favored spot on the cancer cell, keeping its effects under control.

Healthy Soy Intake

Most women, specifically those in countries where soy consumption is comparatively less, need not fear the implications of excessive soy intake. In countries with higher soy consumption, an intake of 20 to 25 mg per day is not uncommon. To clarify, Kucuk said: “If you drink a glass of soy milk, that is about 27 mg of soy.”

For More Information

For more information on Soy and breast cancer, visit the Fred Hutchinson Cancer Center.

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