Misconceptions About Soy

Written By Andrea Poy

Are you one of the many people who were told soy is bad for you? Maybe you were told soy increases estrogen, causes breast cancer, suppresses thyroid function, lowers sperm count, feminizes men, causes dementia, and numerous other accusations. So how can one person tell you soy is harmful while others say soy is a superfood? Let’s discuss where these myths came from and why soy is still negatively talked about, despite high-quality research displaying its many benefits.

Soy Overview

To first understand the popular debate about soy, you must first understand what soy even is. When talking about soy, it is important to distinguish the difference between whole soy foods and processed versions. Whole soy foods include tofu, edamame, soybeans, tempeh, miso, natto, and soymilk. Whereas processed soy includes soy protein isolate, soybean oil, soy lecithin, and soy flour. The research and health benefits talked about in this email are in regards to the whole soy foods mentioned above. Most of soy’s benefits come from its high isoflavone content, a class of flavonoids (an antioxidant compound found in plants). The two major types of isoflavones found in soy are genistein and daidzein. Additionally, whole soy contains fiber, B vitamins, potassium, magnesium, and all 9 essential amino acids. The reason soy has become so controversial is due to its phytoestrogen activity and previous poor research.

What is a Phytoestrogen?

All the misconceptions about soy are due to its high isoflavone content because isoflavones act as phytoestrogens. Phytoestrogens are a type of plant estrogen that have a similar function to human estrogen but with much weaker activity. To say soy increases estrogen levels due to its phytoestrogen content is much more complex than that because phytoestrogens can both increase and decrease human estrogen levels. For example, in premenopausal women with lots of naturally circulating estrogen, phytoestrogens help to decrease estrogen. Being that most women have estrogen dominance nowadays, this is a good thing to help keep hormone levels in check and lessen common estrogen-dominant conditions like endometriosis, uterine fibroids, ovarian cysts, etc. Whereas in post-menopausal women with minimal natural estrogen, phytoestrogens help increase estrogen levels and ease the transition into menopause.

Soy and Breast Cancer

For the longest time, women were told soy was one of the worst things you could eat if you had breast cancer. Unfortunately, some oncologists are still telling their patients this. This misconception all comes down to poor, outdated research. It was not until 2009 that research on soy and breast cancer was extracted from human data. Before then, the only research involving soy and breast cancer was done on cells and animals. Anyone who knows research knows that what happens in cells and animals does not always equate to humans. In several epidemiological studies, there appears to be a linear relationship between increasing soy consumption and decreased risk of breast cancer recurrence and mortality. There also has been no association between soy consumption and increased risk of women with a history of breast cancer.

Soy and Heart Health

A recent review posted in the Circulation Journal touted the numerous benefits of soy intake including a lower risk of heart disease. People who regularly ate isoflavone-rich foods like soy had a moderately lower risk of developing heart disease and were less likely to die from a heart attack. The benefits of tofu were strongest in premenopausal women followed by postmenopausal women, not on hormone therapy.

Soy and Brain Health

Fermented soy foods such as natto, tempeh, soy paste, and soy sauce may provide benefits for those with mild cognitive impairment, Alzheimer’s disease, and Parkinson’s disease due to their antioxidant and anti-inflammatory effects. Fermented soy also helps increase beneficial bacteria and butyrate, a neuroprotective short-chain fatty acid.

Soy and Thyroid Function

Genistein, an isoflavone found in soy, has been considered to be a goitrogen. Goitrogens are substances that interfere with the normal functioning of the thyroid and make it harder for the thyroid to make thyroid hormones. However, a meta-analysis of 18 randomized control trials found soy raised thyroid stimulating hormone (TSH) but had no effect on T3 and T4. Overall, most studies evaluating the effects of soy on thyroid function are not easily comparable due to the different types, quality, and amount of soy products used. Current evidence points toward soy not affecting those with already normal thyroid function. Better research is needed for those with subclinical or overt hypothyroidism.

Soy and Men’s Health

While there have been some studies showing soy decreases sperm count in men, these studies have also shown an increase in sperm concentration and improved motility and morphology. Quality of sperm is of similar importance, if not more important than sperm quantity. Aside from sperm health, a meta-analysis of 41 studies showed soy does not raise estrogen levels in men, lower testosterone, cause erectile dysfunction, or increase breast tissue density. Additionally, observational studies and meta-analyses have found higher soy intake with a lower risk of prostate cancer.

Soy and Menopause

Soy has numerous benefits for menopausal women including reduced frequency and severity of hot flashes, improved bone density, less risk of heart disease, decreased menopause-related weight gain, and decreased risk of breast cancer by 25%.

So there you have it, folks, soy isn’t so bad after all… it’s actually amazing!

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Andrea Poy
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