What Are the Dangers of Drinking Soy Milk?

Soy milk is sometimes linked to breast cancer.
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Many people swap cow's milk for soy milk. If you're making the change and you follow a balanced diet and don't have any particular issues with soy products, you're not likely to face any danger.


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Certain compounds in soy have potential benefits, but when you consume too much processed soy, which is the foundation of commercial soy milk, problems can arise.

On the other hand, if you're eating fermented forms of soy, like miso, tempeh and natto, instead of drinking soy milk, benefits may become noticeable. The key is to make sure you're being choosy with your soy intake and consuming the protein only in moderation.



Processed soy milk can disrupt the way estrogen works in your body and may lead to hormonal imbalances if consumed in excess. Soy milk may also make it harder for your body to digest and absorb important minerals. On the other hand, fermented soy products are more easily digested and absorbed and can help keep your gut healthy.

Soy Milk Dangers

One of the most notable dangers of soy milk involves its isoflavones, which have a chemical structure similar to the hormone estrogen. Because they can bind to estrogen-receptors in the body, isoflavones are classified as phytoestrogens. But here's where it gets a little tricky.


There are two estrogen receptors in the body. When isoflavones attach to one, they produce estrogen-like effects, but when they attach to the other, they have an anti-estrogen effect. Because of this, isoflavones in soy milk have been linked to breast cancer in some cases, but not in others.


A study published in the Journal of the National Cancer Institute in September 2014 noted that estrogen-like activity is beneficial in postmenopausal women, but not in women who have an active menstrual cycle. Because of this, and based on previous studies on soy, researchers concluded that soy milk consumption may be problematic for younger women, but can actually be beneficial for women about 10 years after menopause.

The phytoestrogens may also have negative effects on thyroid function, especially in those with thyroid disease or subclinical thyroid disease or those who are deficient in iodine.

Phytates in Soy Milk

Phytoestrogens aren't the only problem, though. Soy also contains phytates, which are anti-nutrients that can block the absorption of certain minerals, like iodine, zinc, iron, magnesium, copper and chromium. If you're drinking a lot of soy milk and eating processed foods that contain soy, this can increase your risk of developing nutritional deficiencies.

Phytates and phytoestrogens also interfere with metabolism and can lead to increased fat accumulation, weight gain and obesity, according to a February 2012 report published in Food and Nutrition Sciences. Although concerns with soy isoflavones are a big part of soy milk dangers, there are also problems with the way many soy crops are grown, especially in the United States.

Concerns About Genetic Modification

Soy is one of the leading genetically modified, or GM, crops (also called genetically modified organisms or GMOs) in the United States. In fact, the United States Department of Agriculture (USDA) notes that 94 percent of the soy currently grown in the U.S. is genetically modified. In simple terms, genetic modification is when food scientists and chemists introduce new DNA to a crop to make it more resistant to threats, like pests and bad weather, so they can grow more.

While this increases the crop yield, it also introduces potential problems. One of the main concerns is that, since GM crops are resistant to bacteria, they may give way to the growth of bacteria strains that are antibiotic-resistant, and if these antibiotic-resistant bacteria make you sick, they'll be difficult to treat.

Another concern is that the process of genetic modification may introduce toxic substances, like heavy metals, into the plant. If this happens, and you drink a lot of genetically-modified soy milk, it can lead to health problems, like heavy metal toxicity. However, you'd have to drink huge quantities of soy milk over longer periods of time.

Soy Milk and Allergies

Soy is also one of the top eight allergens, and it's possible that genetic modification can make the risk of allergies even higher. According to a report published in the Journal of Food Science and Technology in December 2013, genetic modification can introduce another allergen into the soy milk without the public (or the food manufacturers) even being aware.

The report notes that when patients who were allergic to Brazil nuts, but not soybeans, consumed genetically-modified soy, they showed an allergic immune response. In other words, even if soy isn't a known allergy, there's a possibility that GM soy milk could cause allergy symptoms.

If you're allergic to soy, you'll need to completely avoid soy milk and any processed foods containing it. Unfortunately, soy isn't always listed as such on the ingredient list, so you'll have to watch out for other names for soy, like:

  • Edamame
  • Miso
  • Natto
  • Shoyu
  • Soya
  • Tamari
  • Tempeh
  • Textured vegetable protein (TVP)
  • Tofu

Read more: Soy Protein Intolerance Symptoms

Soy Milk Benefits

Still, there are potential soy milk benefits, especially if you're choosing organic soy milk, which by definition isn't genetically-modified. Soy milk and other whole, soy foods contain B vitamins, fiber, potassium, magnesium, unsaturated fatty acids and high-quality protein. The Harvard T.H. Chan School of Public Health notes that, unlike other plant-based proteins, soy is a complete protein, meaning that it contains all of the essential amino acids you need to stay healthy.

But choosing fermented soy products, like miso, natto, tempeh and soy sauce, may be more beneficial than opting for soy milk. The fermentation process helps break down the soy's sugar and protein content, which makes it more easily digested and absorbed by your body.

Fermentation also introduces some vitamins and minerals that aren't present in unfermented soy products, like soy milk. According to a December 2016 report in Nutrients, natto is a rich source of vitamin K, while other soy products are not.

Read more: The Benefits of Soy Milk - and Some Drawbacks

Don't Overdo It

The bottom line is that, in moderation, organic soy milk and fermented soy products can be part of a healthy diet, but the key is to make sure you're choosing high-quality soy products and not overdoing it. A problem connected to soy milk doesn't really have to do with the milk itself, but instead, with Americans simply consuming way too much soy, especially through processed foods.

Harvard Health Publishing notes that, while it's OK to consume whole soy foods like soy milk, edamame, tofu and fermented soy products in moderation, you should avoid processed foods made with textured vegetable protein and soy protein isolate and soy isoflavone supplements, which contain high doses of isoflavones and may be potentially problematic.