Should I Eat Soy?

You’ve probably heard that tofu, soy milk and other foods that contain soy are good for you, but you might be shying away from them because of rumors that soy contains hormones that can cause health problems. Soybeans contain plant compounds called isoflavones, some of which demonstrate “phytoestrogen” activity, meaning they act a little like the female sex hormone estrogen. Estrogen is linked to breast cancer risk, so many women wonder if eating foods with soy might increase their risk. Some men also pass up soy, worrying that its estrogen-like properties will lower their testosterone levels. Researchers have been studying the effects of soy for years, and based on the available scientific evidence, at Canyon Ranch we believe that soy foods in moderation can be part of a healthy diet for most of us.

Soybeans were first cultivated in China more than 5,000 years ago and soy is becoming more common in American diets. Along with tofu and soy milk, you can find soy in foods like “vegetarian meat” products (soy burgers and soy sausage, for example), miso, tamari soy sauce, tempeh, texturized vegetable protein and soy flour. When you eat edamame at a restaurant, you’re eating soybeans. Soy is naturally rich in protein, and it may help with heart health. Unlike animal sources of protein, soy doesn’t contain cholesterol, and although it does have 5 grams of saturated fat per cup, there’s evidence that soy protein may help lower blood cholesterol levels.

Here are some answers to common questions about soy so you’ll know if you can confidently make it a part of your diet:

Is Soy Safe for Women to Eat?
For most women, yes.
Research about soy and breast cancer risk is somewhat conflicting. Concerns come from studies in rats that show an association between breast cancer and compounds in soy. However, humans metabolize soy differently than other animals, and no such association has been shown in people. Studies have found no higher risk of breast cancer recurrence for those who have already had the disease and consume soy, but the data is limited. There’s some evidence that soy lowers the risk of cancer, including breast cancer, in certain ethnicities and cultures where it’s eaten starting at a young age. How? One possible explanation is that while soy some isoflavones may act like estrogen, they can also block the body’s receptors from more potent natural estrogens we produce.

The bottom line: “At this point, we’re favorable about the moderate use of soy across the lifespan with the possible exception of the breast cancer survivor,” says Lisa Powell, M.S., R.D.N., director of nutrition at Canyon Ranch in Tucson. “We don’t encourage breast cancer survivors to eliminate all soy, just not to emphasize it,” Powell says.

More: 5 Ways to Lower Your Breast Cancer Risk

Is Soy Safe for Men to Eat?
Yes. A 2009 University of Minnesota analysis of 15 studies found that neither soy protein nor isoflavones had an effect on men’s reproductive hormones. Plus, other studies show that soy may protect against prostate cancer. “Soy appears to be safe for men, but we recommend moderation, as opposed to any overemphasis,” Powell says. “It’s a whole food that is rich in plant protein and nutrients that could be included in your balanced diet.”

More: A Male’s Hormones as He Ages

Are Soy Supplements Safe?
It’s best to steer clear of soy supplements. Though many are available (they’re often marketed to women for relief from menopause symptoms), the pills can contain much higher doses of isoflavones than soy foods and are not rigorously tested. Plus, “nutrients in isolation may act differently from the whole food,” Powell says.  “We recommend whole soy foods to take advantage of the synergy among all the nutrients.”

We also don’t recommend soy protein powders or products made with isolated soy protein, as these are extracted using hexane, a cancer-causing solvent.

Are There Any Other Concerns with Soy?
Like other beans, soy can cause gas, bloating and other digestive symptoms. It is also a common food allergen. And high intakes of soy (4 to 5 servings per day) have been shown to decrease thyroid hormone function in some people, particularly those with existing low thyroid function to begin with, Powell says.

Now That I Know Soy is Safe for Me in Moderation, How Can I Work More of It Into My Diet?
A few servings of soy foods over the course of a week are fine for most people. Processed soy foods like soy “ice cream,” protein bars and veggie “not-dogs” contain fewer isoflavones, so choose whole beans like edamame or soy nuts (roasted soy beans) when you can. To work soy into your diet, consider a cup of soy milk over your cereal, or a soy nut butter and jelly sandwich for lunch or edamame as a snack or in a stir-fry for dinner. Soybeans are usually genetically modified, so we recommend organic soy products, which also won’t contain pesticides.

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