What Are the Dangers of Drinking Soy Milk?

Unlike milk from a cow, soy milk has no lactose, which makes it a viable alternative to cow's milk for those suffering from lactose intolerance. Fortified soy milk is a good source of protein, iron, B vitamins and calcium and is low in saturated fats and cholesterol. Although research on soy milk and other soy products has not shown conclusive results, some evidence has suggested that consuming soy milk can have harmful side effects in certain circumstances.

A man is pouring a glass of milk on a bedside table. (Image: Push/Digital Vision/Getty Images)


Allergies to food are the result of your immune system recognizing part of the food as a harmful, foreign substance and attacking it. In the case of soy milk, the harmful part – the allergen – is a group of proteins. In response to the allergen, your body releases histamine and other chemicals into your blood stream, producing allergic symptoms. Allergies to soy milk and other soy products are usually not serious but can be uncomfortable. Symptoms of soy allergy can include redness of the skin, tingling in the mouth, itchy skin, swelling, abdominal pain and runny nose or problems breathing. Severe reactions to soy milk are rare.

Infertility in Males

Soy milk and other soy products contain isoflavones, which are a type of protein. High isoflavone consumption has been linked to decreased fertility in animal studies, according to researchers in the Department of Nutrition at Harvard School of Public Health. The researchers published a study in the November 2008 edition of "Human Reproduction" that reported consuming soy foods lowered sperm concentration.

Thyroid Issues

Drinking soy milk may interfere with your body's ability to absorb thyroid medication, according to the American Thyroid Association. It may also cause issues if you are iodine deficient or have other problems with your thyroid. The isoflavones in the soy milk may lower the amount of iodine in the body, which can lead to underfunctioning of the thyroid. However, the University of Maryland Medical Center points out that in the U.S. most people consume iodized salt, which balances out any iodine lost from consuming soy.


Soy milk contains phytoestrogen, a hormone similar to estrogen. Phytoestrogens may have an effect on hormone-related cancers, particularly breast cancer and prostate cancer. While studies of the effects of soy milk and other soy products on cancer have had mixed results, some findings have raised concerns that consuming soy milk and other products may stimulate the growth of breast cancer cells, according to the University of Maryland Medical Center; however, the research is not conclusive and more studies need to be done. Phytoestrogens may reduce the effectiveness of the breast cancer medication tamoxifen, and the UMMC recommends not consuming soy milk or soy products if you are taking this drug.

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