To Soy or not to Soy?

In the last 20 years, soy has gone from being praised as a great source of plant-based protein to denounced as an estrogenic cheap dairy alternative. This villanization of soy has gone so far as to become part of the modern lexicon as “Soy boy” has become an insult for an effeminate male. So, as always what’s the truth about soy?

Soy or Glycine max is a cultivated member of the bean family and was developed in China sometime before 2,000 B.C. making it a staple crop of East Asia for many centuries. Soy contains molecules called isoflavones which are classified as a phytoestrogen, meaning they act like estrogen in the body. This may sound scary, but phytoestrogens are not as strong as human estrogen, so they have what is called a SERM effect. SERM stands for “Selective Estrogen Receptor Modulator” which is a fancy way of saying that they bind to some estrogen receptors and have an effect similar to estrogen, but it is not as powerful as human estrogen. This SERM activity is very useful therapeutically for multiple conditions. In conditions such as PCOS where estrogen is high, a SERM can block those receptors and help to regulate symptoms related to high estrogen, while still allowing some activity. In conditions where estrogen is low, such as symptoms related to menopause, a SERM can help to replace estrogen without the risks of hormone replacement side effects. There are some studies suggesting that moderate soy consumption in premenopausal woman reduces the risk of estrogenic cancers. This SERM activity makes soy a healthy food to support female health. Regarding male health, there is very little scientific support for men not to eat soy even with these estrogenic effects, however, I would recommend men be more careful around eating soy in moderation and perhaps mix up their plant proteins instead of only using soy products for everything.

Speaking of plant proteins, Soy, while not containing all 20 essential amino acids that make up proteins, contains more than any other plant source. This makes is an excellent source of plant protein for vegetarians/vegans as well as any other person looking to reduce meat in the diet. Fermented soy products such as tempeh or natto are a great source of probiotics so choosing them versus tofu as a protein substitute can add even more benefit.

There are some downsides to eating soy products depending on your school of thought and or individual needs. The majority of soy grown in the US is genetically modified and the US is the top grower of soy in the world at the moment. If you are concerned about GMOs, make sure you are looking for organic products.

Soybeans are a legume, so if your digestive system is sensitive to beans, I would suggest avoiding them. As stated above, soy is traditionally an Asian crop so if you follow the ancestral diet school of thought, then those of East Asian decent should include soy as a stable part of the diet, whereas Europeans or Africans should perhaps avoid it. In the blood type diet, blood type A and AB have low inflammatory responses to soy, whereas type O should avoid it.

Another downside of soy is that it is a goitrogen, meaning that it contains molecules that inhibit iodine from entering the thyroid and thus can reduce thyroid hormone production and cause lumps or “goiters” to form in the thyroid. This rarely has a large enough effect in normal healthy thyroids, but in those with hypothyroidism, it is best to avoid goitrogenic foods to help the thyroid function as efficiently as possible.

So, as you can see, the question of whether soy is good for you or bad for you is complicated and should be decided on an individual basis, not as an all or nothing question. My general advice is usually to eat everything in moderation unless you have a specific reason to avoid it, which holds true for the soy debate as well.

SOURCES:

D’Adamo, D. P. J., & Whitney, C. (2016). Eat Right 4 Your Type (Revised and Updated): The Individualized Blood Type Diet® Solution (Revised, Updated ed.). Berkley.

Kurzer MS. Hormonal effects of soy in premenopausal women and men. J Nutr. 2002 Mar;132(3):570S-573S. doi: 10.1093/jn/132.3.570S. PMID: 11880595.

Chandra Amar K, in Bioactive Foods in Promoting Health, SCIENCE DIRECT, 2010

Farm Flavor, February 14, 2011. Soy What? Soybean Fun Facts, Journal Communications, Inc.