The Controversy of Soy

by Logan Sewall 2 months ago in science

There have been many rumors that soy causes men to become more feminine. I want to examine the science behind these claims.

The Controversy of Soy

The controversy of soy is an interesting mixture of misunderstanding and confirmation bias. I would like to start off by saying there has never been any scientific connection between soy and testosterone levels. Many people like to make the claim that soy has an affect on testosterone levels and will make men more feminine. There is no scientific evidence to back these claims up whatsoever. The majority of these claims come from a misunderstanding of biochemistry and people then latching onto that misunderstanding and spreading it as fact. Media sources who do not cite nor check sources then spread the misinformation to the public.

Where do these claims come from? Claims like this usually don't come out of nowhere and there has to be some basis for the misunderstanding. The basis of that misunderstanding is hormones, specifically testosterone and estrogen. Soy contains what is known as a phytoestrogen, or a plant-based estrogen. When people see this, they assume that a plant-based estrogen will act the same way as the estrogen in the human body; however, this is not the case. Many chemicals synthesized by plants do not act the same way as they would if they were synthesized by the human body. For example, blood contains a protein known as hemoglobin. It is what allows red blood cells to carry oxygen. Plants synthesize heme, the iron containing ligand (ligand is the fancy name for a molecule that can bind to a metal) that makes up hemoglobin. This plant synthesized heme is used in a lot of plant-based burger substitutes because it gives it that meaty flavor, but that doesn't mean you're ingesting plant-made blood. In other words, because it was synthesized by a plant, which has very different conditions then the human body, it does not act the same way it would if it were made in the human body.

The same science can be and has been applied to soy. Many people believe that ingesting a phytoestrogen will decrease their testosterone levels and make them to develop more feminine features. This would be true if they were getting estrogen into their system (taking estrogen or testosterone is the process transgender people people go through to transition), not phytoestrogen. There have been a multitude of studies showing the health benefits of consuming soy, such as reducing risk of prostate cancer. For example, in the papers written by K. S. Weber, et al, and R. M. Sharpe, et al, they distinctly saw no link between phytoestrogen and a soy based diet on testosterone levels and even saw health benefits to a soy diet. [1,2] There have even been studies trying to prove health risks of soy and ended up concluding it is beneficial. [3] Many people against soy like to cite this article without reading it through, because it concludes that soy is not the cause of the issues, it was an isolated incident, and that testosterone levels returned to normal over time.

In summary, there is no link between soy and a decrease in testosterone. Many people like to cite this as a reason not to go vegetarian or vegan or to try and put down people who eat soy, but there is no truth to it. If you eat soy or want to start eating soy and are concerned about your testosterone levels, you have nothing to worry about.

I hope that this helps clear up some of the controversy and that you can help spread the truth. Misinformation is one of the biggest problems in this age. There is so much information out there it is hard to know what to believe. It is best to trust places that cite their sources and can be fact checked. I encourage you to check all the sources of the information you read and do not just assume it to be fact. I encourage you to start reading scientific documents as well. They are written by experts in their field to other experts so they can be wordy, but they are the best source of information. You can see how many times they've been peer reviewed, cited, and what information has been built off them.

Have a great day everyone.



[1] K. S. Weber, K. D. R Setchell, D. M. Stocco, E. D. Lephart, "Dietary soy-phytoestrogens decrease testosterone levels and protate weight without altering LH, prostate 5a-reductase or testicular steroidogenic acute regulatory peptide levels in adult Sprague-Dawley rats," Journal of Endocrinology, vol. 170 (3), 591-599, 2001

[2] R. M. Sharpe, B. Martin, K. Morris, et al, "Infant feeding with soy formula milk: effects on the testis and on blood testosterone in marmoset monkeys during the period of neonatal testicular development," Human Reproduction, vol. 17 (7), 1692-1703, 2002

[3] T. Siepmann, D. G. Edelson, "Hypogonadism and erectile disfunction associated with soy product consumption," Nutrition, vol. 7 (7-8), 859-862, 2011

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Logan Sewall

A Chemist and Nature Photographer born and raised in Alaska. I’m here to share my stories and pictures of nature as well as my work as a scientist. My goal is to inspire people and to provide scientific information to help drive change. 

See all posts by Logan Sewall