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Is Soy a Healthy Choice Where Cancer Is Concerned?

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When choosing foods for a balanced diet, some healthy choices are easier to identify than others. Fruits and veggies may have a clear edge over deep fried foods, but some foods, like soy, fall somewhere in the middle. 

The effects of soy came into question when early studies in rodents found that isoflavones, a compound that’s found in many foods but is especially concentrated in soy, increased the growth of estrogen receptor-positive breast cancer cells and promoted breast cancer growth. However follow up studies in humans showed that rodents metabolize soy differently and that the effects of soy may actually be beneficial to humans.

“Most experts agree that although there isn’t enough strong evidence to recommend soy as a cancer preventative food, it does appear safe and could possibly be helpful for cancer survivors,” said Abigail Galbraith, an oncology dietitian at Samaritan Hematology & Oncology Consultants.

The American Institute for Cancer Research and World Cancer Research Fund, which put out recommendations regarding cancer, have placed soy into a neutral category meaning it doesn’t seem to cause cancer or prevent cancer. Other foods in the same category: coffee, dietary fiber and non-starchy vegetables. The group recommends a moderate consumption of one to two servings a day of whole soy foods like tofu, soymilk, edamame or soy nuts.

How Much Soy?

According to Galbraith, if you’ve had cancer and soy was a part of your diet before, it’s fine to continue eating a moderate amount of soy, up to three servings a day. Studies of Asian populations with lifelong moderate soy consumption show that it could help prevent breast cancer. But if soy is new to your diet, stick to the guidelines of one to two servings a day, where a serving contains 7g of protein and 25mg of isoflavones.

Isoflavone content isn’t typically given in the nutrition facts and can vary widely depending on how the soy is prepared and by brand. The United States Department of Agriculture has a partial list of isoflavone content of common foods if you eat soy regularly and are concerned about your intake. One cup of soymilk can be as low as 6 mg and 3 ounces of uncooked tempeh can be as high as 51.5 mg. Tofu is about 19 mg.

“Soy can affect people differently based on their own gut bacteria and genetics,” said Galbraith. “There is a considerable amount of scientific research right now around soy and how it affects the body. We’re constantly learning more.”

Eat whole soy foods with confidence as part of a healthy diet, but Galbraith recommends avoiding soy pills, isoflavone-enriched powders and soy protein powders due to the extremely high isoflavone content.

“A plant-based diet has anti-inflammatory properties that are a keystone for cancer prevention and recurrence,” said Galbraith. “Having tofu instead of meat is a positive switch that can reduce your overall cancer risk, especially if you’re replacing red meat.” 

According to the American Institute for Cancer Research and World Cancer Research, certain foods can increase or decrease your cancer risk.

Foods with Strong Evidence to Decrease Cancer Risk:

  • Whole grains
  • Fruit
  • Colorful vegetables
  • Whole foods not supplements

Foods with Strong Evidence to Increase Cancer Risk:

  • Processed meat(e.g. ham, salami, bacon)
  • Red meat (e.g. beef, lamb, pork)
  • Alcohol

Cancer Survivors are invited to join a That’s My Farmer nutrition series which will be returning to your community soon.

Learn more about the Mediterranean Diet and healthy food preparation at three seminars this May and June.