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You are what you eat, they say. But what happens when what you eat contains … hormones? The narrative around soy has created a dilemma for consumers, sparking a debate about whether we should eat foods like miso, edamame and tempeh. In 2008, researchers chronicled the unusual case of a man who developed breasts and other side effects after drinking three quarts of soy milk per day — and from there, a myth was born. But experts are tired of the myths around what they call a highly beneficial food, which contains plant hormones that act similarly to estradiol, known more commonly as estrogen in humans. “Soy foods represent one of the healthiest and easiest ways to consume more plant protein,” said Dr. Mark Messina, director of nutrition science and research at Soy Nutrition Institute Global, and has been conducting research on soy since 1989. Advertisement Here’s what scientists want you to know about integrating soy into your diet. What is soy? Soy is a plant-based product that’s high in protein and domesticated in China. It can be eaten as a whole soybean or turned into many other foods, such as tofu or soy milk. People have turned to soy as a source of multiple vitamins like B, C and K, and minerals like zinc and iron. “Soy is packed with nutrients beyond its well-known isoflavones,” said Lauren Manaker, a registered dietitian in Charleston, South Carolina. “It’s a fantastic source of high-quality plant-based protein, fiber and essential nutrients like calcium, iron, magnesium and potassium. It’s also naturally low in saturated fat, making it a heart-healthy choice. These nutrients work together to support muscle health, digestion and overall wellness.” Messina added there are three ways to incorporate soy: traditional Asian soy foods, concentrated protein in powders that are in meat alternatives, energy bars, or can be added to liquid and also supplements. Advertisement Despite myths, soy doesn’t contain the type of hormones that humans produce. Instead, they have a high concentration of isoflavones, a type of plant estrogen. Why soy has gotten a bad rap After that case of the man who developed, well, man boobs, the myth started circulating. “The male feminization concern rose to the forefront beginning in 2009 because of an article in a very popular men’s magazine. By the way, 10 years later, that magazine in an article entitled ‘Tofu is the New King of Protein’ apologized for their misunderstanding of the scientific literature,” Messina said. Other research has proven that not only is this concern just a myth, but that soy has benefits, he added. Advertisement “In contrast to this case report, human intervention studies involving nearly 2,000 men show no effects of soy or isoflavones on testosterone or estrogen levels,” Messina continued. “In addition, soy does not increase risk of gynecomastia (breast enlargement in men) or affect sperm or semen parameters. ... Finally, soy protein also promotes gains in muscle mass and strength in men engaged in resistance exercise training similarly to animal protein, including whey.” Another common concern is whether soy can cause cancer. This has also been disproven, and some studies, in fact, suggest it might play a role in preventing it instead. “Much of the confusion around soy and cancer risk has been due to studies in rodents and a misunderstanding about a phytochemical that is naturally found in soy foods called soy isoflavones,” said Dr. Marissa Shams-White, senior principal scientist for the department of population science at the American Cancer Society in Atlanta. “However, we now know that rodents break down soy isoflavones differently than humans, so they don’t have the same effect on us. In fact, they may bind to estrogen receptors in our bodies and block estrogen from binding to them, which may help to prevent the growth of breast cancer cells.” Advertisement She added that more research is needed to understand how soy may provide these benefits, but studies suggest that soy foods may have antioxidant and anti-inflammatory effects. Messina even said he recommends girls consume at least one serving of soy daily: “an amount associated with a reduced breast cancer risk in the observational studies.” Advertisement Not all soy is created equal While it might seem easy and efficient to just add a soy supplement to your diet, rather than learning about and cooking soy-based foods, experts warn that might not be as effective as other options. “The findings are mixed when isoflavones are consumed through supplements,” Shams-White said. “For cancer prevention, we do not recommend taking supplements.” Instead, nutrition experts recommend turning to food to reap the benefits of soy. “Women can benefit from 1-2 servings of soy per day, which provides about 25-50 mg of isoflavones,” Manaker said. “This amount doesn’t necessarily change with age, but during menopause and perimenopause, soy may play a more significant role in managing symptoms. For men, soy is perfectly safe and doesn’t negatively affect testosterone levels, as some myths suggest. The same serving range applies, and it’s a great addition to a balanced diet for both men and women.” Advertisement Dr. Andrea Caamano, medical director for The HRT Club, a digital health platform for hormone health in New Jersey, touts the benefits of soy for menopause symptoms, specifically hot flashes. For example, in a 2023 study of a plant-based diet including soy, women had a drastic drop in hot flashes, with an 84% decrease in 12 weeks. For 59% of participants, the hot flashes ended altogether. Caamano recommends people always choose food products in their “most natural, organic state,” which helps avoid overly processed food, including soy. “Soybeans work best for hot flashes and weight loss, are a whole food, and contain lots of fiber and protein,” she said. “Tofu is a decent runner-up as it is usually lightly processed, but once we get into soy milk and soy yogurt, there tend to be additives, sugar, etc., making these products less natural and potentially causing a worsening of hot flashes and weight gain,” she said. The best foods for integrating soy into your diet For those looking to reap the benefits of soy, Manaker recommends the following snacks and meals: Edamame — by itself, or added to salads Tofu — can be used in stir-fries, soups, or other types of bowls and meals Tempeh — a protein-packed addition to meals Roasted soy nuts — a satisfying, crunchy snack Soy milk: milk made by soaking soybeans How much soy is good for you? “The recommendation is to consume 25 grams of soy protein per day for cholesterol reduction. That is easy to do when using concentrated sources of soy protein,” Messina said. “Soy protein directly lowers blood cholesterol levels.”
