What Is the Connection between Soy Milk and Estrogen?

Soy milk and estrogen are linked because soy products contain chemical species called isoflavones. These molecules, also known as phytoestrogens, can have effects similar to estrogen in the human body. Normally, the estrogen produced by humans has a number of functions, including regulating the reproductive system. Many people are interested in the effect that isoflavones have on the human body, especially whether they can be used to treat symptoms of menopause, and if they have any negative effects on infants fed soy-based formulas.

Products made from soy, including soy milk, contain chemical species called isoflavones. Another term for isoflavones is phytoestrogens. These compounds occur naturally in plants, and affect the body in a similar way as estrogen. Some researchers hypothesize that plants produce these chemical compounds as a mechanism of defense against herbivorous predators. Eating plants containing phytoestrogens could decrease the animals’ reproductive capabilities, resulting in a lowered population over the years.

In order to understand the effects that eating isoflavones can have on people, it is helpful to understand the role that estrogens play in the human body. Estrogen is a member of a class of chemical compounds called hormones: these molecules are produced to help regulate the internal environment of the body. Although both men and women produce estrogen, this hormone is present in a higher concentration in women. Estrogen is important for developing female secondary sexual characteristics, regulating the menstrual cycle, increasing the ability of the blood to clot, reducing cholesterol levels in the blood, maintaining strong bones, and increasing water retention in the body.

Many menopausal women are interested in the connection between soy milk and estrogen because they are sometimes advised to drink soy milk to decrease symptoms such as hot flashes. Since menopause is a time when women’s estrogen levels are dropping, it is thought that phytoestrogens can act as a substitute for estrogen in the body and reduce some menopausal symptoms. Unfortunately, the amount of soy milk a woman would have to drink in order to effectively reduce symptoms is not well established.

Some parents and doctors worry about the link between soy milk and estrogen because some babies are given soy-based formulas instead of breast milk or cow’s milk-based formulas. They are concerned that ingesting phytoestrogens could affect the babies’ growth and development. A number of investigations into the health of infants given soy-based formulas have not shown any significant problems with growth, future reproductive status, or overall nutritional status. Soy-based formulas are therefore still an option for infants, but are typically only recommended if the baby cannot process certain milk-based sugars or if the parents prefer a plant-based diet.