Soy is a controversial topic in today’s wellness world. It is touted for its health benefits by some health experts, while simultaneously being deemed a health risks by others. Here is what you need know:What is Soy?
Soy (soybean) is a legume that has been cultivated and consumed for thousands of years in China and as of more recently, has become popular in the US. Often times soy is considered the “go to” protein source for vegetarians and vegans and a dairy free alternative for those allergic, sensitive, or intolerant to cow’s milk.
Soy-based foods come in a variety of forms from whole to highly processed. Whole soybeans (edamame) and soy nut butter can be found at most grocery stores. Minimally processed soy products include soy milk, soy flour, tofu, and fermented soy (miso, tempeh and soy sauce) are also common. Processed soy can be found in plant-based burgers, sausage, cheese, protein bars and protein powders, and also as textured soy protein.
Let’s start by discussing the health benefits of soy. Soy is a complete source of protein and provides us with essential fatty acids (omega-3 & omega-6), fiber, minerals (magnesium, potassium, copper, and manganese), and phytonutrients (plant chemicals) called isoflavones. Additionally, soy has natural anti-fungal, antibacterial, and antioxidant properties meant to protect the plant, and which may also be beneficial to humans.
Fermented soy products are often perceived as healthier than non-fermented soy foods, and the fermentation process seems to increase the total available protein and bioactive compounds and reduce anti-nutrients naturally found in soy. In addition, fermentation of soy with lactic acid bacteria and probiotic yeast significantly increases its antioxidant activity. Fermented soy may also play a role in preventing type 2 diabetes as studies suggest that it may improve insulin sensitivity.
Controversies and Research
Let’s take a look at some of the controversies surrounding soy and the related research. This is by no means and exhaustive list, but it highlights some of the more popular topics:
- Thyroid– There is concern about whether soy foods act as goitrogens or disrupt thyroid function in any way. Early research suggests that soy isoflavones interfere with the enzymes required for thyroid hormone synthesis. However there appeared to be no associated adverse effect on circulating thyroid hormone, thyroid weight, or thyroid tissue. Animal research does demonstrate significant unfavorable anti-thyroid effects from defatted soybean consumption (not soy isoflavones) if iodine deficiency is present. Researchers conclude that a combination of individual and other dietary goitrogenic factors may be involved. So, their recommendation is to limit/avoid raw or sprouted soy due to its potential goitrogenic effects. Cooking, however, will deactivate most goitrogens.
A Japanese study reported “hypometabolic symptoms (malaise, constipation, sleepiness)” and goiter in subjects consuming soy for three months and noted that symptoms disappeared when soy was eliminated for one month. Though, it is not clear if the study used raw or cooked soybean and full text is not readily available. A comprehensive 2006 review of the literature ultimately finds little to no evidence soy or soy isoflavones put forth negative effects in healthy, iodine-replete individuals. Functional medicine expert Dr. Hyman, MD notes that it would take an exceedingly large amount of soy to disrupt thyroid function and that soy may only affect those with iodine deficiency.
Human studies on thyroid restrictions appear to be inconclusive. Research on isolated soy protein suggests that 56 mg daily intake of soy isoflavones (from isolated soy protein) promoted increased free thyroxine index and T4 levels over time while a 90 mg/d dose was associated with increased thyroid stimulating hormone and increased T3 over time. Ultimately researchers concluded that the small effects soy protein may have on thyroid hormone levels are likely to be clinically insignificant.
- Cancer– Currently, soy is being researched for its potential role in fighting breast, colon, lung, prostate, and stomach cancers. Although the evidence that soy may reduce risk of colon, lung, and prostate cancer is limited, the evidence is somewhat stronger for breast and prostate cancer prevention.
- Cardiovascular Disease– relating to cardiovascular disease, research suggested that large amounts (~50 grams per day) of soy protein, given in place of animal protein, could reduce total cholesterol, LDL, and triglycerides reducing cardiovascular risk. However, of course, it’s important to keep in mind that reducing blood cholesterol may not reduce risk of cardiovascular disease so clinical effects and outcomes may be insignificant.
The FDA is currently reevaluating the claim though ongoing research suggests that soy (especially soy protein and isoflavones) may have additional beneficial effects on cardiovascular health including reduction of diastolic blood pressure, slowing atherosclerotic progression, and improvement of endothelial function.
- Genetically Engineered Soy-Lastly, we can’t forget to mention that approximately 90% of soy today is genetically engineered to be resistant to glyphosate and other herbicides.
There is concern that genetically engineered crops may have negative health effects (such as tumors, liver and kidney damage, digestive issues, etc.). The potential for increasing allergenicity is another concern regarding these crops.
- Anti-Nutrients- In its raw form, soy contains anti-nutrients that can bind with minerals, interfere with digestion, and disrupt organ function. However, it should be noted that many of these elements are neutralized when soy is cooked, processed, or fermented.
So, what’s the truth? As of yet, there is no definitive answer. There have been thousands (yes, thousands) of studies done on soy and its effects on humans, human cells, and animals. While soy has been praised for its role in the prevention of conditions like heart disease, menopausal symptoms and breast cancer, it has been criticized for its role in disrupting thyroid function, endocrine balance and reproduction.
Overall, research suggests soy may inhibit and induce specific enzyme function, act as an antioxidant, support glutathione and detoxification pathways, inhibit actions helping control tumor growth, and support neurotransmitter metabolism.
The bottom line is that when it comes to soy consumption, quality and moderation are important. It is best to choose organic, non-GMO whole soy products and limit soy consumption to no more than 1-2 servings per day. Fermented soy may be tolerated better than non-fermented due to the increased bioavailability of nutrients and reduction in anti-nutrients.
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Basilia Theofilou is a contributor on our blog as well as one of the nutrition advisors here at PreviMedica. You can read more about her here.