Who knew April is "National Soy foods month"? Soy consumption is highly controversial, confusing, and conflicting, yet growing in America as it is a $4.5 Billion industry. A few years back, I was stunned when I heard a patient tell me they didn’t want to give their son soy milk because it will decrease his testosterone levels. This was the first time I had heard of this and understood see her concerns. There is no question more human research needs to be done. We also need to continue to be cognizant that food effects everyone differently, and it is only one (although major) out of many changeable factors that play a role in our overall health. So I want to clear a few confusions on soy.
The low down
Soy is considered a top major allergen in the United States. It contains all the essential amino acids. The benefits of soy consist of improving cardiovascular health, skin health, menopausal symptoms, visual cognition, and improved kidney functions. Other advantages include reducing chances of breast cancer, prostate cancer, and decreasing depressive symptoms. It's a good source of iron, zinc, potassium, protein, fiber, and B vitamins. In the United States, 90% of soy made has been genetically modified to upgrade the soy protein and enhance the oils to be heart healthy. Genetically modified foods is a whole different topic as it is controversial, like soy.
There is whole soy, fermented soy and then there is soy protein isolate (SPI). Whole soy consists of tofu, soy flour, edamame, and soy milk. It is a high quality protein, containing all essential amino acid. Fermented soy is what’s found in soy sauce, miso, tempeh. SPI is found in many vegan products like protein powders, meal replacements, and vegan burgers. SPI is highly processed, removing essential nutrients like the fiber, fat, and carbohydrates.
Soybean has a compound called goitrogens which block iodine uptake in the thyroid gland which could lead to hypothyroidism or goiter (enlarged thyroid) when taken in excessive amounts. It is important to note these conditions are rarely due to soy consumption, as the US average per capita for soy intake is only 2 grams a day. Adequate amount of iodine is necessary always, but definitely when consuming soy. Iodine is a nutrient necessary for metabolism, reproduction and thyroid function and can be found in seafood, seaweed, and eggs. Consuming a diet with a variety of foods and cooking your soy foods can decrease its goitrogenics effects.
Soy protein contains a phytoestrogens which mimic the effects of estrogen. It's believed that the weak exposure of isoflavones reduces chances of breast cancer, especially when consumed in childhood and adolescence before becoming an adult. High levels of isoflavone have been shown to increase breast cancer but the ones found in soy foods are too low to have that effect. Soy and isoflavone supplements (the processed soy) however have shown to increase risk of breast cancer due to its high levels of isoflavones. It's advised to avoid the processed soy like SPI and supplements, and moderately consume whole soy foods.
Soybean is known for its estrogen levels from the phytoestrogen compound. But many human studies (over 30 meta-analysis studies) have shown that soy consumption does not decrease the male sex hormone, testosterone. One study, did show it decreased when consuming SPIs, so I would recommend stirring clear of the highly processed soy. If decreased testosterone levels from soy is a concern, be aware that consumption of alcohol, mint, and vegetable oils, and other foods may decrease testosterone levels.
Things to consider
When reviewing information on food and your health, ask yourself these questions:
1. What is the source?
2. Who is funding the research?
3. What type or variety (in this case type of soy) was consumed?
4. Was the research based on humans or animals?
Long story short
Soy is an excellent source of protein with many health benefits. If you are worried about negative effects on health, avoid SPIs, limit your consumption to 1-2 servings a day and consume the whole soy foods that are organic and non-genetically modified. If you are still not sure, consult with Registered Dietitian and Licensed Nutritionist.