While not technically milk, soy milk, produced from the soybean plant, provides a popular dairy alternative for those who cannot or choose to not consume cow's milk. Although soy milk provides many potential health benefits, such as lowering heart disease risk and protection from prostate cancer, some past research has suggested that it may have negative side effects for men when consumed in large enough quantities.
Soy Milk Composition
Soy beans are rich in phytoestrogens, a subcategory of a group of antioxidants called isoflavones. The structure of these plants' estrogens are very similar to that of the human sex hormone estrogen. This similarity can sometimes allow phytoestrogens to either mimic or inhibit the hormone in human estrogen receptors. Accordingly, these compounds in soy beans have the potential to play a role in any biological process that involves estrogen, leading many to speculate that soy might "feminize" men if consumed too often.
Some research has suggested that dietary intake of soy and the subsequent addition of plant estrogens can reduce sperm concentration in men. Although these studies found the reduction to be small, it was considered statistically significant. Other research has suggested that large doses of soy may lead to erectile dysfunction and behavioral concerns such as more aggressive and submissive behavior.
However, for every study condemning soy milk, there are just as many contradicting these negative findings. Designing and carrying out a research study on a single component in a food and interpreting the results is extremely complex. Additionally, these inconsistent findings are further complicated by the fact that much of the research is underwritten by industries with vested interests. It's also worth noting that a large percentage of studies were carried out on animals that were often given far greater amounts of isoflavones than any human would ever consume.
Overall we can conclude that in the case of soy milk, it is the dose that makes the poison. Consuming soy milk in moderate amounts has not been shown to have a negative impact on male health. On the contrary, the beneficial nutritional prospects make it a viable and wholesome milk alternative.
Sarah Dreifke is a freelance writer based in DeKalb, IL with a passion for nutrition education and the prevention of chronic disease. She holds a Bachelor of Science in both Dietetics and Life Sciences Communication from the University of Wisconsin-Madison. Currently, she is working towards a combined Master's Degree in Nutrition and Dietetics as well as a dietetic internship at Northern Illinois University.