Does drinking soy milk make men’s breasts grow?

The concern about the effect of soy on men probably arose because soy and other legumes contain isoflavones. These are phytoestrogens, or estrogen compounds structurally similar to human estrogen. However, they have different biological properties than human estrogen and do not promote estrogen’s harmful effects on the body, Hensrud says. In fact, they can be protective.

In general, studies do not support the idea that drinking soy milk will cause men to grow breasts or experience any other feminizing effects. Studies also refute the idea that soy increases the risk of breast cancer in women.

I have not seen any data that would lead me to believe that drinking soy milk or eating soy products promotes feminization in men, i.e. breast growth, or any similar adverse health effects, such as cancer of breast, in women, says David Jenkins, university professor in the departments of nutritional sciences and medicine, Temerty Faculty of Medicine, at the University of Toronto. I recommend soy intake to my patients of both sexes. I don’t think it has any bad effects. He added that no major health organization has warned of any danger associated with soy consumption.

At least two early studies each described a single case of soy consumption being linked to feminizing effects in men, including enlarged breasts, erectile dysfunction and decreased libido. But the experts noted that both subjects consumed unusually high amounts of soy in one case, three quarts of soy milk a day, which is many times the average dietary intake.

That’s a very large amount of soy milk on a consistent basis, most people don’t drink that much water on a daily basis, Hensrud says. These are two unusual cases and are not representative of the overall evidence on soy phytoestrogens.

Breast growth gynecomastia occasionally occurs in males and adolescent males, he says, referring to other causes of gynecomastia in young men. Most importantly, there is strong evidence that soy intake provides numerous health benefits with little risk.

Many studies have also found that soy milk and other soy products can reduce the risk of breast cancer, possibly explaining the low incidence of breast cancer among Japanese women, whose traditional diets are high in soy. According to studies, soy intake can also reduce the risk of breast cancer recurrence in women.

Women who have estrogen-positive breast cancer may be concerned about soy, but Hensrud says the data doesn’t point to an increased risk. Other research indicates that breast cancer rates increase among Japanese women who reduce their soy consumption and adopt a Western diet.

In addition, soy milk may have cardiovascular benefits by reducing blood pressure, inflammation, and low-density lipoprotein (the bad) cholesterol, according to studies. Additional research shows that soy appears to reduce the risk of prostate cancer and may prevent memory loss associated with aging and cognitive decline.

What else should you know?

Soy milk is a processed food that may contain added sugar, flavors and other ingredients. Also, those who are allergic to soy should avoid it.

In addition to isoflavones, soy foods are rich in B vitamins, fiber, potassium and magnesium. Also, unlike some plant proteins, soy protein contains all nine essential amino acids, making it a complete protein. Soy foods can be unfermented or fermented, the latter meaning that they have been cultured with beneficial bacteria, yeast or mold.

Hensrud says fermented soy milk may have even more health benefits, like other fermented foods.