Does soy really affect breast cancer risk?

February, 27th, 2025

, Answer Section, ,

No. Eating soybeans or food that contains soy will not raise a person’s risk of breast cancer. Looking across populations, research finds that eating foods with soy may lower the risk of breast cancer. But it isn’t clear whether soy supplements are safe for people who’ve had breast cancer or who are at high risk of breast cancer.

Long-term contact with the hormone estrogen is a risk factor for breast cancer.

Soybeans contain plant chemicals called isoflavones. When digested by some people, some isoflavones act a little like estrogen that’s made in the body.

But plant estrogens in food are weaker than estrogen made in the body. And isoflavones may help lower the effect of estrogens made by the body. In some people, the action of isoflavones may block the body’s estrogen in some tissues. In other tissues, isoflavones may act as a weakened form of estrogen.

Breast cancer risk from estrogen is linked to lifelong exposure:

• Getting your period, also called menstruation, at a younger age than typical.
• Late start of menopause.
• No pregnancies or first pregnancy at an older age.
• Hormone therapy history with estrogen and progestin.

Other factors that raise the risk of breast cancer are:

• Age.
• A family history of breast cancer or genetic changes that make cancer more likely.
• Alcohol use.
• Dense breast tissue.
• Obesity after menopause.
• Breast or chest contact with radiation.

If you have questions about your risk of breast cancer, talk with a healthcare professional.

Soybeans and foods with soy can be part of a healthy eating pattern. Soy milk and yogurt, with added vitamins and calcium, are nutritionally similar to dairy milk and yogurt. And there are about 56 to 83 milligrams of isoflavones in 1 cup (240 milliliters) of soy milk.