When it comes to health and aging, we’re very conflicted about soy. At the end of the 20th century, soy quickly earned a health halo reputation (facilitated perhaps by soybean industry marketing?). It was supposed to cure or prevent all kinds of illnesses, from heart disease to breast cancer to hot flashes in menopause. Then just as suddenly it fell out of favor, thanks to rumors of increased breast cancer risk and hormone disruption.
Soy exists in our food supply in two distinct forms:
- soy foods, like tofu or edamame or soy milk
- processed foods containing soy-derived ingredients, such as soy isoflavones or soy protein isolates.
Soy protein isolate is protein that has been extracted from processed soybeans. Because soy beans are high protein, these isolates are used in plenty of food products to boost protein content, from protein powders and bars to fake meat to breads and cereals.
Soy isoflavones are phytoestrogens — molecules with weak estrogen-like behavior — present in all soy foods. Because of that, people theorized that soy isoflavones might affect breast tissue and increase cancer risk. Most studies of isoflavone intake do not show any evidence of increased cancer incidence or higher death rates for cancer survivors. In fact quite the opposite. Many studies show benefits of soy isoflavone intake. Another concern is the impact of these estrogen-like chemicals on children who consume soy formula. Could phytoestrogens disrupt normal growth in children? Again, studies have not found evidence for this. Despite the evidence, fears remain and some people avoid soy foods.
Humans have been consuming soy for centuries. Primitive soy plants originated in China, and soy was originally used more for medicinal purposes than as a food. Soy became a staple food in China and a variety of fermented soy foods had been developed by the 1st century B.C. Soy cultivation spread around Asia, but soybeans were not introduced to Europe and the Americas until around the 18th century.
It’s important to understand that soy foods have been used by humans for centuries, without obvious health problems, so current fears about health risks seem unfounded. Nevertheless, one catch is that until relatively recently, soy consumption was limited to foods like tofu, miso, tempeh, soy oil and soy milk. Now, thanks to widespread use of soy protein isolate, consumption of soy isoflavones could be much higher for some people.
I wrote about soy in relation to menopause in my book “Food Wisdom for Women”. A recent article in Food and Nutrition Magazine supports much of what I wrote. One of the main points is that soy is neither savior or villain. For example, it’s not linked to higher risk for breast cancer, but then it’s not know to prevent breast cancer. While women in Asian countries with high soy intake may have lower rates of cancer, there are many other diet and lifestyle differences in those countries that can also impact risk.
What about hot flashes? There’s no consistent evidence for a benefit, but then soy foods can be included in a healthy diet, which is one of the best defenses against severe menopause symptoms. What about heart disease? Again, soy doesn’t magically prevent heart disease. In fact, as the article points out, the FDA recently revoked the heart disease label claim permitted for soy foods, because evidence for that claim was weak. But substituting soy foods for high fat meat products can improve your diet and lower your overall risk for heart disease.
What about soy oil?
Soybeans have been pressed for oil for centuries, starting in China. Today most of the world’s soybeans are processed for oil. Soy oil is much like any other vegetable oil: high in unsaturated fatty acids, which are recommended over saturated fats.
Soy oil is widely used in processed foods, from bakery items to salad dressing, and sold for home use, although these days it’s usually labeled “vegetable oil” rather than “soy oil” (check the ingredients list if you’re curious). Perhaps that labeling distinction is made in response to fears about soy.
To Soy or not to Soy?
There’s really no reason to actively avoid soy foods for health reasons, unless you’re allergic to soy. High protein soy foods like tofu or soy milk or edamame are a good addition to any healthful plant-based diet. If you’re determined to avoid soy, you need to read food labels, as many processed foods contain soy.
I personally don’t avoid soy, but I don’t eat soy foods all that frequently. Soy foods like tofu, miso, edamame have been consumed for centuries; soy burgers and soy cheese, not so much. You don’t need soy. It’s not likely to prevent diseases, and adding soy to a junky diet won’t be helpful. So choose accordingly.