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Study: Does eating soy affect the risk of death in breast cancer survivors?

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Contents

At a glance Guidelines
Findings     In-depth        
Clinical trials Limitations                
Questions for your doctor             Resources                    


STUDY AT A GLANCE

This study is about:

Whether eating soy is associated with a higher risk of death in breast cancer survivors.

Why is this study important?

Whether women who have had breast cancer should eat foods that contain soy has been debated for many years. Research examining soy’s effect on breast cancers has been mixed; it is still unclear whether women with breast cancer should avoid soy products or eat more soy than they did before their diagnosis.                                                                  

Study findings: 

  1. Women diagnosed with breast cancer whose diet contained the highest levels of soy products (more than 1.5 mg daily) before or after diagnosis had a reduced risk of dying from any cause (not just breast cancer) compared to breast cancer survivors who had the lowest level of soy in their diets (less than 0.3 mg daily).
    • This association was limited to women who did not previously receive hormone therapy as part of their breast cancer treatment, including those with hormone-receptor-negative () breast cancers.

What does this mean for me?

This study suggests that breast cancer survivors who had a higher dietary intake of soy had less risk of dying from any cause than breast cancer survivors who ate less soy. However, researchers do not completely understand how soy affects breast cancer growth or risk for recurrence.  More work needs to be done in this area, especially for women who have breast cancer. 

It is important to remember that this study adds to what we know about soy consumption and breast cancer but it does not provide definitive conclusions for specific patients. Not all breast cancers are the same, so research that applies to one subtype may not apply to all subtypes. A report by American Cancer Society written by experts in nutrition, physical activity, and cancer survivorship and published in 2012 assessed available research regarding nutritional intake (including soy) for breast cancer survivors; the report stated that, “Current evidence does not suggest that consuming soy foods is likely to have adverse effects on risk of recurrence or survival.”  Ultimately, health care providers know their patients’ cancers and situations best. Women should discuss their concerns with their health care providers, and continue to follow their recommendations regarding soy consumption.

Posted 4/27/17

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References

Rock CL, Doyle C, Demark-Wahnefried W, et al. “Nutrition and physical activity guidelines for cancer survivors.CA: A Cancer Journal for Clinicians, 62: 242–274.  

Zhang FF, Haslam DE, Terry MB, et al. “Dietary Isoflavone Intake and All-Cause Mortality in Breast Cancer Survivors: The Breast Cancer Family Registry.” Cancer. Published online first in March 2017. 

This article is relevant for:

This article is also relevant for:

people with breast cancer

people with metastatic or advanced cancer

people with triple negative breast cancer

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IN DEPTH REVIEW OF RESEARCH

Study background:

Soy consumption by people with breast cancer is controversial among researchers and health care providers, and that controversy often confuses patients and survivors. Some research shows that dietary soy acts against breast cancer development by decreasing the amount of made by the body. On the other hand, other research shows that dietary soy can act like , activating the signaling pathways that encourage breast cancer growth.

While studies from China have consistently found a lower risk of breast cancer recurrence and/or risk of death associated with higher soy consumption in women, studies conducted in the United States have yielded mixed results.

Fang Fang Zhang and colleagues from Tufts University and other institutions published work in the journal Cancer in March 2017 looking at soy consumption and risk of death from any cause (not just breast cancer) in women who have been diagnosed with breast cancer.

Researchers of this study wanted to know:

How does eating soy products affect the risk of death in women who have had breast cancer?  

Population(s) looked at in the study:

The researchers used the Breast Cancer Family Registry to survey women from San Francisco, New York City, Philadelphia, Utah, and Ontario (Canada) who had invasive breast cancer. Information on the women’s tumor hormone status ( and progesterone receptors) was taken from pathology reports or from cancer registry records.  Researchers obtained mortality data in various ways, including annual telephone contacts and questionnaires.

These women completed questionnaires that included information on their diets. Of the 6,235 women who participated, 4,769 returned the questionnaire within 5 years before they were diagnosed (pre-diagnosis), while 1,466 returned the questionnaire within 5 years after they were diagnosed (post-diagnosis). The women were asked how frequently they consumed certain foods (including soy) and the portion size.  Average follow-up was 113 months (9.4 years), during which 1,224 deaths occurred.

Study findings: 

  1. Women with breast cancer whose diets contained the highest levels of soy products (more than 1.5 mg daily), whether pre- or post-diagnosis, had a reduced risk of dying from any cause (not just breast cancer), compared to breast cancer patients who had the lowest levels of soy in their diets (less than 0.3 mg daily).
    • This association was limited to women who had hormone-receptor-negative (ER-/PR-) breast cancers and women who did not previously receive hormone therapy as part of their breast cancer treatment.   

Limitations:

Because the researchers used a self-reporting survey to measure soy intake, the results are subject to certain data collection errors, including the possibility that participants incorrectly remembered how often they ate a particular food or how much of it they ate. (Data from women whose reported total calorie intake was much higher or much lower than the average caloric intake of other participants were considered to be unreliably reported and were excluded from the results.) Women who had higher soy intake were more likely to be Asian American, young, premenopausal, physically active, more educated, not overweight or obese, nonsmokers, and either did not drink alcohol at all or drank less than 7 alcoholic drinks per week. To ensure that the effect on risk was due to soy consumption and not any of these other factors, the researchers adjusted for this information in their mathematical models. Finally, the researchers looked only at all-cause mortality, meaning deaths that were not breast cancer specific; they were unable to look at breast cancer recurrence. The researchers did not have additional information on any other diseases that the women may have had, which may have also increased the risk of death.

Conclusions:

This study suggests that women who have breast cancer and regularly consume soy products have a lower risk of dying from any cause. However, more work needs to be done to understand and confirm these findings. Breast cancer patients should continue to follow their doctor’s recommendations regarding soy consumption during and after treatment. Women who are worried about their dietary intake of soy or any other nutrients should discuss their concerns with their health care providers.

Posted 4/27/17

Share your thoughts on this XRAYS article by taking our brief survey

References

Rock CL, Doyle C, Demark-Wahnefried W, et al. “Nutrition and physical activity guidelines for cancer survivors.CA: A Cancer Journal for Clinicians, 62: 242–274.  

Zhang FF, Haslam DE, Terry MB, et al. “Dietary Isoflavone Intake and All-Cause Mortality in Breast Cancer Survivors: The Breast Cancer Family Registry.” Cancer. Published online first in March 2017. 

Expert Guidelines
Expert Guidelines

Nutrition for people diagnosed with cancer

The National Comprehensive Cancer Network (NCCN) recommends the following for cancer survivors: 

  • Think about your food choices and the amount of fruits, vegetables and unrefined grains you eat compared with red and processed meats, alcohol, and foods or beverages with added fat or sugar. 
  • Think about your eating habits, including portion size, snacking, how often you eat out and the use of added fats or sugars.
  • All survivors should be encouraged to:
    • Make informed choices about food to ensure variety and adequate nutrient intake.
    • Limit refined sugars.
    • Eat a diet that is at least 50% plant-based, consisting mostly of vegetables, fruit and whole grains.
    • Track calorie intake; monitoring calories is an effective way to manage weight.
    • Minimize alcohol to no more than one drink per day for a woman and two drinks per day for a man.
  • For patients desiring further dietary guidelines, the USDA approximate food plate volumes are:
    • Vegetables and fruits should comprise half the volume of food on the plate
    • Vegetables: 30% of plate; fruits: 20% of plate
    • Whole grains: 30% of plate
    • Protein: 20% of plate
  • Recommended sources of nutrients:
    • Fast: Plant sources such as olive or canola oil, avocados, seeds and nuts, and fatty fish.
    • Carbohydrates: Fruits, vegetables, whole grains and legumes.
    • Protein: Poultry, fish, legumes, low-fat dairy foods, and nuts.

The Academy of Nutrition and Dietetics, the United States Office of Disease Prevention and Health Promotion and the American Institute for Cancer Research also publish expert guidelines on nutrition and health. 

Updated: 12/12/2021

Questions To Ask Your Doctor
Questions To Ask Your Doctor

  • Is it safe for me to eat soy products?
  • What is a good, balanced diet for me?
  • What is a healthy body weight given my age, size and health?
  • Can you refer me to a nutritionist?

Open Clinical Trials
Open Clinical Trials

The following are studies focused on nutrition for people diagnosed with breast cancer. 

Visit our Featured Research Page and Research Search and Enroll Tool to find additional studies enrolling people with or at high risk for cancer.

Updated: 05/31/2024

Peer Support
Peer Support

The following organizations offer peer support services for people with, or at high risk for breast cancer:

Updated: 05/07/2024

Find Experts
Find Experts

The following resources can help you locate a nutritionist near you or via telehealth

Finding nutritionists

  • You can find a registered dietician in your area through Eatright.org, the website for the Academy of Nutrition and Dietetics. Search for nutritionists by specialty, including "cancer," "weight management" and "heart health."


Related experts

  • The Livestrong at the YMCA program includes a free 12-week membership and fitness training with certified exercise experts. You can search by zip code for a program near you.  


Other ways to find experts

  • Register for the FORCE Message Boards and post on the Find a Specialist board to connect with other people who share your situation. 
  • The National Cancer Institute (NCI)-Designated Comprehensive Cancer Centers have specialists to manage the symptoms and side effects of cancer prevention or treatment. 
  • FORCE partners with Savor Health® to provide free, personalized, evidence-based nutrition support 24/7 and “on-demand" through their text-based Intelligent Nutrition Assistant (Ina®). You can subscribe here

 

Updated: 11/20/2023

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