The first time I heard about plant estrogens was back in University, when I met a vegetarian who was deathly afraid that eating soy would cause him to grow breasts. Since I already had breasts (and wasn’t particularly scared of having them grow) I didn’t give the matter much more thought.
I started hearing about the issue again in 2009, after the birth of my first child. One of my friends (who is pretty health conscious), was very concerned about the affect of soy on developing children. She advised me not to let my daughter eat soy. I was skeptical, since I knew many asian moms who seemed to have perfectly healthy children in spite of feeding them a host of soy products. I did a bit of research and was satisfied that the occasional bit of tofu or miso wasn’t going to transform my kid into a space alien.
Fast forward a few years later, and soy is one of the most common concerns raised by people who are concerned about the safety of a vegan diet. I was perfectly satisfied that soy was safe, but I wanted to gather some more specific information to provide concerned readers of my blog and my YouTube subscribers. One of my subscribers, Renzee White, has been encouraging me to make a video/blog post on this topic for a while, so this is for you, Renzee!
There are a number of issues people bring up surrounding soy, but the most consistent is concern about possible estrogenic activity. This concern is obviously more pronounced in men, who worry that drinking soy milk or eating tofu might cause them to develop “man boobs.”
Now, I’d be pretty happy to develop boobs at this late stage, man or other wise. But in my own (limited, anecdotal) experience, this doesn’t seem to be a side effect of following a vegan diet. In related anecdotal evidence, my husband is free from man-boobs as well.
Soybeans contain molecules known as “isoflavones.” Isoflavones appear to have a weak estrogenic effect, and are popular in the natural health industry as a treatment for hot flashes in menopausal women. And since sex hormones like estrogen are used to grow breasts in transgendered patients, many have feared that soy itself may have similar breast-boosting affects.
What does the medical research tell us about soy and hormones?
The most comprehensive source of information on soys’ health effects in the long term comes from studies on soy infant formula. Soy milk is often used in children who are allergic to cow’s milk formula or are intolerant to lactose. In 2004, a study of 48 children raised on soy formula showed exactly zero cases of precocious puberty, breast growth or other problems associated with sex hormones. A comprehensive study published in the journal Fertil Steril showed that soy did not have feminizing effects, even when soy was consumed at levels much higher than those of asian men. This has been the case in repeated studies.
So we have proven that phytoestrogens do not cause an increase in human estrogen levels, nor do they reduce testosterone. And yet paranoia keeps many men from consuming soy out of a false belief that it might “feminize” them. This could not be farther from the truth.
On the other hand, soy can actually help with a number of health issues that threaten public health. Soy has been linked to reduced risk of coronary heart disease and cancer. In fact, some studies go so far as to encourage plentiful soy consumption early in life, since it’s been shown to reduce the risks of so many diseases.
Of course, there’s always an outlier – an interesting study published in 2008 featured the only case of gynecomastia strongly associated with soy consumption. It featured an elderly man who was drinking 3 litres (3 quarts) of soy milk each day. He had no other symptoms of hormonal abnormalities, but complained of breast tenderness. When he stopped consuming 1,200 calories worth of soy per day, his symptoms disappeared. Of course, his symptoms could easily have come from the extra calories (our bodies store estrogen in fat cells), so even in this odd case, it’s not easy to determine whether the soy – or the fat it produced – was the cause of his symptoms. Regardless, you should be fine if you keep your consumption with in normal limits.
Dairy and hormones
For a moment, let’s try just using common sense. What do you think might have more effect on your hormone levels: soybeans, or the lactation fluid of a pregnant mammal? (most cows are pregnant nearly the entire time they are being milked).
If you said cow milk, you’d be right. And there is a lot of science to back up your “hunch.”
A study published in the Journal of Reproductive Medicine showed vegans give birth to twins at just 1/5th the rate of milk drinkers. The author of the study postulated that this difference could be caused by an increase in the presence of IGF-1 (insulin growth factor) in milk drinkers. In addition to increasing the risk of having twins, IGF-1 is also associated with cancer, and has led some researchers to suggest that is why plant based diets reduce the risk of cancers compared to vegetarian or omnivorous diets.
What about the effect of hormones in milk on pre-pubescent children? In 2010, researchers demonstrated that intake of milk from pregnant cows significantly increased the presence of estrogen and progesterone in both men and women, and decreased testosterone production in men (in other words, what people always worry about with soy, but doesn’t actually happen!). The researchers concluded:
The present data on men and children indicate that estrogens in milk were absorbed, and gonadotropin secretion was suppressed, followed by a decrease in testosterone secretion. Sexual maturation of prepubertal children could be affected by the ordinary intake of cow milk (source)