Soy has been a staple food in many cultures for centuries, but for many years it’s been a controversial topic in the cancer community. So, let’s separate fact from fiction so you can decide if soy belongs in your diet.
What Are Phytoestrogens?
Soy contains compounds called phytoestrogens. These plant-based compounds are structurally similar to human estrogen, but much weaker.
Phytoestrogens can bind to estrogen receptors (ERs) in the body. The effect depends on the type of receptor involved. Some receptors have a proestrogenic effect in tissues, while others have an antiestrogenic effect. In other words, the binding may mimic estrogen in some cases and block estrogen in others. In fact, in some cells, this results in tumor growth suppression triggering cancer cell death.
Finally, estrogen receptors aren’t just located in reproductive tissue. They’re also found in bone, lung, liver, colon and fat tissues, plus the urinary, cardiovascular and central nervous systems.
Types of Phytoestrogens
Two main phytoestrogens are lignans and isoflavones. Isoflavones are the most concentrated in soybeans, making soy the focus of much debate. Smaller amounts are found in other legumes, grains, and vegetables.
Soy: Friend or Foe?
Animal Studies
Early rodent studies linked high doses of isoflavones to increased breast cancer risk. However:
- Rodents metabolize soy differently than humans.
- The doses used were far higher than any realistic human diet.
Human Studies
In contrast, human research shows soy is safe and may even be protective:
- Large studies (Shanghai Breast Cancer Survival Study, LACE, WHEL) found soy intake of more than 10 mg/day was associated with a 25% reduced risk of breast cancer recurrence.
- A 2025 review exploring phytoestrogens in triple-negative breast cancer showed promise as a potential therapeutic agent.
- Asian populations, where soy intake averages 25–50 mg/day, consistently show lower breast cancer risk compared with women in Western countries (who typically consume less than 2 mg/day).
Beyond Isoflavones: Other Benefits of Soy
Whole soy foods are nutrient-dense and offer:
- B vitamins, potassium, magnesium, and high-quality protein.
- Fiber to support gut health and the immune system.
- Reduced LDL (“bad”) cholesterol and improved blood pressure.
- Potential reduction in menopause hot-flash symptoms.
Practical Takeaways
Trust your gut. If soy makes you anxious, focus on including other wholesome, plant foods – fruits, vegetables, legumes, whole grains, nuts, and seeds.
If you choose soy, stick with organic, and both whole and minimally processed options like:
- Tofu
- Edamame
- Unsweetened soy milk
- Fermented foods (tempeh, miso) – BONUS: they also support gut health and may improve nutrient absorption.
The Bottom Line
Soy is just one piece of the puzzle. A healthy lifestyle extends beyond nutrition to include regular physical activity, adequate sleep, and mental health practices supporting stress management and emotional well-being.
For most people – including cancer survivors and thrivers – moderate soy intake from whole foods can safely be part of an overall healthy diet and lifestyle.
Co-Written by: Mark S. Shahin, MD, FACOG, FACS and Erin Pellegrin RD, LDN
Helpful Links:
- Soy Isoflavones
- Straight Talk about Soy
- Soy and Cancer Risk: our Expert’s Advice
- Soy and Cancer: Myths and Misconceptions
- Will eating soy increased my risk for breast cancer?
- Phytoestrogens
- How Phytoestrogens Can Have Anti-Cancer Estrogenic Effects
- Breaking Barriers; Phytoestrogens in the Fight Against Triple-Negative Breast Cancer: A Comprehensive Review
- The Women’s Study for the Alleviation of Vasomotor Symptoms (WAVS)
- Is Soy Bad for You?