Maybe you’ve heard scary things about soy. . .
Feminizing men, fueling breast cancer, wrecking your thyroid. Three claims, decades of research, and a solid conclusion.
If you live in a country where soy isn’t a staple food, you’ve probably heard a lot of scary things about it:
If you live somewhere that eats a lot of soy, you’re probably thinking: these myths are ridiculous. We’ve eaten soy for generations and I’ve never heard of anyone having these problems. You’re right, and you have nothing to worry about.
For everyone else, here’s the scientific consensus on soy foods, and the three myths that really need to die☠️.
What are soy foods?
Soybeans start out green and tender — you may have seen these served as edamame. As the beans mature they get smaller, and most varieties turn yellow. From there, they’re remarkably versatile.
Soy milk
Soybeans blended with water, then strained to remove the pulp.
Tofu
Made from soy milk: ingredients bring the proteins together, much like curds and whey in cheesemaking, and the proteins are pressed into blocks.
Soy curls & TVP
Made much like wheat noodles: soybeans are ground into flour, mixed with water into a dough, then formed into shape.
Tempeh
Similar to making cheese: a culture is added to the beans and grows around them.
Why is there so much fear around soy?
Soy contains phytoestrogens — plant estrogens. Phytoestrogens are different from mammal estrogens, the kind humans, cows, and goats produce. Much of the fear comes from that single fact, plus the misunderstanding that eating phytoestrogens must be like taking estrogen.
If people knew how many everyday foods contain phytoestrogens, soy might not seem so frightening:
The only people worried about eating too much garlic are vampires. Meanwhile, dairy products contain actual mammal estrogens and almost nobody worries about those.
Just because dairy products contain animal estrogens. You don't need to start worrying about them. Low-fat dairy, especially fermented dairy like yogurt and kefir, can be part of a Whole-Food Mediterranean-Style diet.
Look at the health outcomes, not the mechanism
Most soy fear-mongering zooms in on one chemical or biological process. It’s a common social media move: highlight a single process and make it sound terrifying. The problem is that thousands of processes are running in your body at once, and for every “bad” one there may be dozens counteracting it.
Smoking cigarettes activates plenty of “positive” biological processes: appetite suppression, improved alertness, better working memory. The long-term outcomes still bury the short-term benefits. That’s why outcomes — not mechanisms — are what we judge a food by.
The three myths and the actual health houtcomes
“Soy feminizes men and lowers testosterone”
Many men worry that eating soy will shift their hormones or cause gynecomastia — “man boobs.” Soy has been studied extensively, and it has been consistently demonstrated to have no effect on men’s hormone levels, including testosterone and estrogen. There’s also no data suggesting soy affects sex drive or causes gynecomastia.
“Soy increases breast cancer risk”
The opposite is true. Higher soy consumption is associated with a 30% reduction in the risk of developing breast cancer, and eating soy during childhood and adolescence is probably a factor in achieving that reduction. For women who have already received a breast cancer diagnosis, soy consumption reduces recurrence rates and improves survival.
The mechanism is that phytoestrogens interact with beta estrogen receptors — but again, the outcome is what matters: less breast cancer, and better survival for those who have had it.
“Soy harms thyroid function”
This one traces back to case reports of infants developing goiters — usually caused by the thyroid not getting enough iodine. The authors hypothesized the soy infant formula was responsible. In a way they were right, but not because soy was affecting the thyroid: the diet was deficient. When iodine was added to the soy formula, the way iodine is added to cow’s milk, the goiters improved. So does soy affect thyroid function? Iodine affects thyroid function, soy does not.
So how does soy actually affect your health?
Soybeans are a bean, and beans come with a long list of positive outcomes. Here’s what has been studied specifically for soy.
Type 2 diabetes & cardiovascular health
Meta-analysis · 1,963 studies · highest vs. lowest soy intake
Soy consumption is associated with lower disease risk.
Prostate cancer
Prostate cancer is the second most commonly diagnosed cancer in men, and soy consumption is significantly associated with a reduced risk of prostate cancer.
Breast cancer
Soy consumption is linked to lower rates of developing breast cancer and, for those already diagnosed, lower rates of dying from it.
Bone health
A meta-analysis of 5,313 articles found soy food consumption associated with improved bone mineral density in the lumbar spine, hip, and femoral neck — protective against osteoporosis.
Hot flashes
Frequent, regular consumption of soy products lessens menopausal hot flashes.
The bottom line
The overwhelming scientific consensus is that soy is a beneficial food. If you want to add it to your diet, start small: steam some in-the-pod edamame, toss dry-roasted edamame into a salad or trail mix, or make marinated tofu for dinner.
Educational content; not a substitute for medical advice.
