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SOY: Good or Bad?

While I was in Los Angeles last week, I shadowed a renowned medical doctor in Beverly Hills. During my three-day preceptorship, there were many patients who asked my opinion about their diet and nutritional intake. The most interesting question was from a patient who claimed she had soy sensitivity. Upon questioning her further, I realized she had endometriosis and she was scared that soy would make her condition worse. On my way back to Toronto, I started thinking about the controversy around soy and how important it is for people to know the good and the bad side of soy.

Soybeans contain phytoestrogens that are called isoflavones. By Phytoestrogen, I mean that the isoflavones attach to estrogen receptors and act as a very weak estrogen. It is believed that phytoestrogen or plant based estrogens have 1/100(0) strength of animal based estrogen. Age plays an important role on phytoestrogen strength. In young people, the human estrogen is very strong so the effects of phytoestrogens are negligible. However, as we age human estrogens will become weaker so phytoestrogens get an opportunity to bind harder to estrogen receptors and have an effect. What is interesting is soy seems to have both estrogenic and anti-estrogenic effect in different tissues in human.

Positive effects of soy:
1. Regulates LDL (bad cholesterol) levels because of high level of fiber
2. Regulates cell growth and protects against many cancers including breast and prostate cancer
3. It does not affect uterine fibroids as it becomes anti-estrogenic in uterus
4. Decreases blood pressure by increasing blood vessels diameter via producing nitric oxide
5. Improves bone density in menopausal women by acting estrogenic
6. Contains high protein content (this is only true when taking soy products like miso, edamame, or tempeh. Remember soy protein isolates act like cow’s milk. They increase insulin like growth factor [IGF-I] and increase risk of developing cancer)
7. Some studies report between 30-55% reduction in hot flashes and night sweats in menopausal women


Bad effects of soy:
1. Decrease absorption of medication in GI tract (it is recommended to take it at least 2 hours away from medications like thyroid medication, or the medication dose needs to be adjusted)
2. Difficult to digest in some individuals
3. Decrease thyroid function because they have phytate that acts as trypsin (thyroid hormone) inhibitor
4. Blocks uptake of minerals such as calcium, zinc, iron and magnesium again due to phytate contents
5. Most soy products are genetically modified
6. Some companies use hexane to process soy products. Hence, it is a good idea to know the company that processes the soy


Bottom line:
• Avoid processed soy because all the good nutrients are gone so you are basically getting nothing
• Make your own soy milk or buy soy milk made of whole-bean (on the label)
• If you have ever been diagnosed with breast cancer, remember that there are no convincing data that is safe or unsafe. I personally think it is better to AVOID it if you have a past medical history of any estrogen dominant condition
• As many other products, look at the expiry date. The longer it is the more additive and processing is involved in the product.


My recommendation is don’t take more than 15-20 gr of soy a day. However, feel free to enjoy your miso soup, edamame or soy latte whenever you wish to do so.
Dr. Z
Picture taken from: http://pilladvised.com/2010/05/the-soy-luck-club/

Author resumes no liability for incorrect information or any action reader decides to take based on the information on this blog post. This blog post is only author’s personal input on the topic and by no means entails any medical advice.