Soy: Friend or Foe? | Knowledge is Power


In the past several decades, soy has developed a negative reputation as a systemic endocrine disruptor that should be avoided. This article sheds new light based on recent research on the protein.

by jbarowski (New)

Specializes in pediatrics, special needs, education. Has 5 years experience.

Soy's comeback: Is eating Soy good or bad?

Soy: Friend or Foe? | Knowledge is Power

Soy is a nutrient-dense food that's a staple of vegan and vegetarian diets. Edamame, shelled or in the pod, makes a savory snack as immature soybeans, while miso is a rich soy paste that's popular in Japanese cuisine. Soy sauce, a fermented soybean dressing, is commonly added as a topping to many dishes. Soy serves as a versatile meat replacement when it's extracted from the soybean plant. Tofu is commonly made with a soy base. Imitation meats are also rich in soy.  In past studies, its use as a regular staple in meat-free diets has been questioned. 

Soy contains high levels of isoflavones, a phytoestrogen, or plant estrogen. While isoflavones are much weaker than the estrogen a human produces naturally, this compound still binds to estrogen receptors. In past studies, researchers hypothesized that the compound could act as a systemic endocrine disruptor, causing negative effects on the body. As an endocrine disruptor that mimicked estrogen, studies suggested that the compound either acted as a weaker form of estrogen, or it had anti-estrogen effects, preventing the effects of estrogen. 

Studies conducted in the past have suggested that soy could have dramatic effects as an endocrine disruptor, affecting thyroid function, ovulation levels in women, and semen production in men. A recent systematic review of 417 past studies shed new light on these suggestions, offering new considerations on soy and its place in the diet. 

There are some issues to be addressed with past studies regarding soy and its title as an endocrine disruptor. While soy has been studied immensely in the past, there are concerns with making broad conclusions about the negative health considerations associated with the protein. Most of the past studies on soy have been conducted on animals. There are current indications that soy may be processed differently in animals than in humans, making prior assumptions inaccurate. Meanwhile, the processing of this protein can be different from person to person based on their current medical profile. This also makes it difficult to draw broad conclusions on soy's effect on everyone. 

Additionally, many forms of soy can be studied. Tofu and soybeans preserve the structural integrity of soy, while the highly processed versions may have other effects on the body. Blanket statements don't adequately consider the effects different forms of soy have on humans.

The 417 studies that were recently reviewed contained data on soy protein and humans, proving to be more applicable than prior studies. Contemporary research shows that soy can be safely consumed multiple times a week. Up to five servings a week can be safely recommended to patients. 

Those with hypothyroidism should monitor their soy intake, and refrain from taking their medication within 4 hours of consuming the protein. Though this research is limited and based on a single study, this rule should still be recommended until further research is done. 

The most beneficial form of soy to consume is minimally processed. Tempeh, tofu, miso, and edamame are less altered forms of the protein. Meat replacement products, soy bars, and soy-based protein powders contain fewer nutrients as they are not complete forms of soy. The key to consuming soy is mixing the plant protein into a well-balanced diet. 

Unprocessed foods rich in soy may have minimally positive effects on the cardiovascular system. By replacing some portions of meat protein with soy, the patient can lower their risk of developing heart disease.  These foods also provide nutrients necessary for healthy blood vessels, reducing inflammation and increasing elasticity. 

The isoflavones found in soy aid in reducing the uncomfortable symptoms associated with menopause. As a phytoestrogen, this compound binds to estrogen receptors, slightly improving hot flashes. There are also indications that they can improve fatigue, joint pain, vaginal dryness, and anxiety with this population. It may decrease the progression of osteoporosis associated with menopause. Further research is needed in this area to confirm the amount of soy and type that is most likely to bring about these positive patient outcomes. 

Studies conducted in various parts of the world indicate that soy may be protective against breast cancer, due to its role as a phytoestrogen. The amount of soy consumed seemed to reduce the amount of breast cancer in the studied populations. Soy consumption may also reduce the recurrence of other types of cancer, including prostate. 

There are indications that fermented soy products may have a role in reducing the prevalence of neurological disorders. Soy is considered an antioxidant, potentially allowing it to minimize the oxidative stress caused by Alzheimer's disease and Parkinson's disease. It can also diminish inflammation in the brain, and slow the progression of cognitive decline. 

There are many protective qualities associated with implementing moderate amounts of minimally processed soy in a well-balanced diet. Past studies have been proven inaccurate in their assumptions on the negative consequences of this complete protein. This may be recommended, with the approval of a healthcare provider, to patients who have thyroid functions within normal limits.

Medical Disclaimer: The information on this site is not a substitute for professional medical advice.


Neither soyfoods nor isoflavones warrant classification as endocrine disruptors: a technical review of the observational and clinical data

Straight Talk About Soy

Is Eating Soy Healthy or Unhealthy?

Nurse Janelle is a masters educated nurse who focuses on provided high-quality content to her consumer base. As a nurse writer, she crafts well-researched health and wellness topics for nurses and the general public.

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1 Comment(s)

Tweety, BSN, RN

Specializes in Med-Surg, Trauma, Ortho, Neuro, Cardiac. Has 30 years experience. 30,852 Posts

Great article.  The "soy is bad" myth is one of the most frustratingly persistent nutrition myths out there, along with "carbs are bad and make you fat".

Hong Kong has the longest lived population in the world and also drinks the most soy milk per capita.  Japan has the next longest lived population in the world eat a lot of miso, natto and tofu.  

I've been eating tofu and tempeh for about 30 years a couple of times a week and will continue to do so.