Is soy safe for patients with breast cancer?

When it comes to eating soy foods, there are a lot of myths about what’s safe for cancer survivors and patients in cancer treatment.

As a breast cancer survivor and senior clinical dietitian at MD Anderson, Christie Siebel is passionate about debunking misinformation so patients get the nutrients they need to stay healthy.

Siebel shares this advice for patients and survivors who seek to avoid soy.

Soy foods are safe for patients with cancer

Siebel stresses that soy is generally safe to eat. “Soy is a great alternative to animal protein to include in your daily diet,” she says. “There’s no reason to avoid eating soy.”

Soy contains phytoestrogens – the plant form of hormone estrogen. Because the names sound similar, Siebel says there has been hesitation around eating phytoestrogen, especially among patients with breast cancer and other types of cancer that are hormone-sensitive.

For many breast cancer patients, treatment involves blocking estrogen to prevent cancer cells from forming.

Though they sound similar, these hormones aren’t the same, and eating phytoestrogens doesn’t affect the estrogen found naturally in your body.

Soy foods may reduce your risk of cancer

Research suggests eating soy foods may reduce risk of cancer recurrence – even in patients with estrogen receptor-positive cancer. “Soy isn’t bad for you, and it may actually be beneficial for cancer prevention,” Siebel says.

This may be especially true for patients who carry a BRCA mutation. These genes are responsible for DNA repair. It’s thought that isoflavones found in soy may restore tumor suppression in BRCA1 and BRCA2 genes.

“That’s why I try to eat soy every day,” says Siebel, who carries the BRCA gene.

How soy foods impact your health

There are three main types of foods that come from soy. Each one has a different impact on your health, Siebel says.

• Whole soy foods. These include edamame, unsweetened soy milk and tofu. Siebel says these are the healthiest options. They’re often less processed and contain more plant-based protein.
  
  
• Soy supplements are often powdered and can be included in bars, smoothies and shakes to boost protein intake. “If you’re including soy supplements in your diet, don’t overdo it,” Siebel says. She recommends talking to your care team about how much protein you need to achieve your health goals.
  
  
• Condiments like soy sauce, soybean oil or soy lecithin may be found in things like salad dressing. Since these don’t contain as many phytoestrogens, they don’t offer many health benefits. But they’re not necessarily harmful if you eat them in small amounts, Siebel says. You should still watch how much soy sauce and other condiments you consume since it is high in sodium and can increase your risk of  high blood pressure and other health issues. 

Depending on your other dietary needs, Siebel says two servings of soy foods a day can be part of a healthy diet. “A serving could be half a cup of edamame, or an eight-ounce cup of soy milk,” she says.

Talk with your care team about your needs

The bottom line, Siebel says, is to have good communication with your care team for any questions you may have about your diet and cancer risk.

“Work with your dietitian and care team to make the best decisions for you,” Siebel says. “But there’s no reason to avoid eating soy.” 

Request an appointment at MD Anderson online or by calling 1-877-632-6789.