Health Mythbusters: Soy Consumption

By: Nikita Nayak

Does Eating Soy Cause Hormone Imbalances?

Soy, a nutrient-dense source of protein, is a popular food all around the world, especially in Asian countries where foods like tofu are important parts of numerous meals. However, there are many widespread beliefs about the harmful effects it may have on the human body. The prevailing belief is that soy consumption leads to imbalances in estrogen levels, causing a variety of health issues, from cancers like breast cancer and cervical cancer, to different thyroid disorders. Given that large numbers of people are consistently consuming significant amounts of soy, it is important to understand its effects on the human body.

How Would Soy Affect Hormone Levels?

Soy contains high concentrations of isoflavones, which are plant estrogens and function similarly to human estrogens, but with weaker effects. These phytoestrogens can bind to estrogen receptors in the body, mimicking naturally occurring estrogens. This can cause either estrogenic activity or anti-estrogenic activity. This can have varying effects based on the existing estrogen levels in the body and whether or not a woman is premenopausal or postmenopausal.

What The Research Says:

A 2004 study investigated the link between soy and cancer by comparing the effects of different dietary treatments given to mice and found a positive connection between soy consumption and cell proliferation. They found that mice who were given diets enriched with the compounds found in soy had stimulated tumor growth when compared with mice who were given regular diets (Allred et al. 2014). Other studies have found that one specific compound found in soy (genistein) enhanced the growth of breast cancer cells in mice (Kwon 2014; Allred et al. 2001).

Other studies have found that soy consumption either has no effect on human hormone levels or has a positive effect. For example, some studies showed that soy consumption may have effects that help with cancer prevention as it can have anti-estrogenic effects in the body (Kurzer, 2002; Trock et al., 2006; Zhao et al., 2019). Other studies found that while soy consumption may have a negative effect, it doesn’t have a large enough effect to result in observable changes like disorders or tumors. For example, a 2019 study found that while soy consumption did increase the levels of TSH (thyroid stimulating hormones), it did not raise them enough to be clinically significant (Otun et al., 2019)

Summary:

The research on the topic of soy consumption and its effects on hormones has produced varied and conflicting data. However, the argument that soy consumption has little to no effect on hormone levels is more plausible due to the number of studies that came to the same conclusion and the fact that many of them were clinical studies conducted on humans over long periods of time rather than mice models.
Ultimately, the effect of soy consumption will vary from person to person based on their age, gender, race, existing hormone levels, etc. So, the decision to eat soy or not will have to be a personal one.