Soy: Does Soy Lower your Testosterone levels?

You might've heard a lot about soy while growing up about how it is rich in protein and good for growth. But as you entered your adulthood, you certainly have come across warnings to minimize soy consumption for some reasons( such as infertility and low libido).

Is there any harm in soy? Let's find out.

What is Soy?

Soy (derived from soybeans) is present in some canned and packed foods and especially found in soy milk, soy sauce, soybean paste, soy lecithin, edamame (immature soybeans in the pod) and tofu. It is also every so often added to foods like bread, cereals, and meat products. Soy is used as a meat substitute in vegetarian products such as soy burgers and soy hot dogs. There is no arguing that soy is a good source of protein.

Maybe this will come as a surprise to you, but an average person consumes a lot more soy than they realize. This is probably because soy comes as an indirect ingredient in most of the food you buy.

Are there any benefits of Soy?

National Nutrient Database prepared by the United States Department of Agriculture's (USDA) claims that 90 grams of cooked green soybeans contain about 127 kilocalories (kcal), 11.12 g of protein, 5.76 g of fat, 9.95 g of carbohydrate and 3.8 g of fiber.

While soybeans are low in saturated fat, they are high in protein and vitamin C. They are also a good source of calcium, iron, fiber, phosphorus, magnesium, potassium and thiamin.

However, the nutritional content of all those soy products out there varies in regards to how they have been processed and what other ingredients have been added.

Does soy have estrogen in it?

It's not like soy brings estrogen to your body. Estrogen is a hormone and soy doesn't have as its content.

Nevertheless, soy contains a kind of compound known as isoflavones (genistein, daidzein, and glycitein) which take the role of phytoestrogens or plant estrogens in the human body. Phytoestrogens aren't exactly the female hormone, estrogen, yet, they are structurally similar to estrogen. It is also assumed to have similar effects on the body. The American Journal of Clinical Nutrition explains it here.

High estrogen levels in men are more or less a direct path to low testosterone levels. Eating soybean or drinking soy milk, which contains estrogenic compounds, is often considered to be something that would lower testosterone.

So, how does Soy affects Testosterone levels?

Let's ponder over the following studies and make a conclusion after that.

  • Asian Pacific Journal of Cancer Prevention published a study with a conclusion that higher consumption of soybean and green tea are strongly related to the establishment of a capacity for equol production. What's wrong with equol? You might ask. See, equol is a strong anti-androgen. It can almost completely hold back the activity of dihydrotestosterone (DHT).
  • The study titled ' Soy food and isoflavone intake in relation to semen quality parameters among men from an infertility clinic' examined the association of soy foods and isoflavones intake with semen quality parameters. The researchers assessed the intake of 15 soy-based foods of 3 months of the 99 subfertile men who presented for semen analyses to the Massachusetts General Hospital Fertility Center. The association of soy foods and isoflavones intake with semen quality parameters was determined while adjusting for personal characteristics. After analyzing the results, the researchers came to a conclusion that higher intake of soy foods and soy isoflavones is associated with lower sperm concentration.
  • Another study titled ' Hypogonadism and erectile dysfunction associated with soy product consumption' also analyzed a human subject. As the test subject, a 19-year-old man was made to introduce heavy quantities of soy in his diet. Subsequently, the subject was found to have diminished libido and began to experience erectile dysfunction as well. When his blood sample was analyzed, a significant decline of DHEA, testosterone, and DHT levels were found. As part of the research, the man was made to stop consuming soy for one year. Consequently, his erectile health and hormonal profile were completely recovered. This case emphasizes the impact of isoflavones in the regulation of sex hormones and associated physical alterations.
  • Society for Experimental Biology and Medicine published a study which involved feeding soy in male infant rats while they were still in the womb. It turned out in the end that these rats had a problem with sexual organ development afterward. A strikingly similar conclusion was made in this study published by the official journal of Society of Toxicology.
  • The study titled 'Stimulatory influence of soy protein isolate on breast secretion in pre- and postmenopausal women' indicated that prolonged consumption of soy protein isolate has a stimulatory effect on the premenopausal female breast, characterized by increased secretion of breast fluid, the appearance of hyperplastic epithelial cells, and elevated levels of plasma estradiol. The findings suggest an estrogenic stimulus from the isoflavones genistein and daidzein contained in soy protein isolate.
  • The Journal of Nutrition made the concerns clear with a study titled ' Soy protein isolates of varying isoflavone content exert minor effects on serum reproductive hormones in healthy young men' which involved the participation of healthy men as subjects. The study concludes that soy protein, regardless of isoflavone content, decreased DHT and DHT/testosterone with minor effects on other hormones.
  • Another study published in the same journal proves that dietary treatment with soy at physiological concentrations produces blood levels of genistein sufficient to stimulate estrogenic effects, such as breast tumor growth. Breast cancer is a clear indication of inflated estrogen.
  • This study published by a different journal also confirms the aforementioned claim.

Soy protein and bodybuilding

Soy protein has been used for bodybuilding by men for ages. There are even some products out there in the market that provides soy protein exclusively. With such concentration of proteins in it, there is no doubt that soy can assist in bodybuilding and muscular growth. However, excessive intake of soy can lead to undesirable effects as pointed out by scientifically backed studies.

How much soy is too much for a man?

You are in serious trouble if you are kind of person who drinks soy milk daily and includes soybeans in your diet. There is no need to worry as long as you don't remember the last time you had soy.

A study which included healthy young men as subjects found that two scoops of pure soy protein powder which contains about 56 grams decreased blood testosterone levels by 19 percent after four weeks. However, testosterone levels increased within two weeks of skipping the protein powder.

Meanwhile, another clinical trial found that a soy-dairy protein supplement at a rate of 22 grams per day for three months did not alter testosterone in young men doing resistance training all the while muscle strength increased.

If accepting the above study, we can consider 22 grams a day a safe level of soy consumption.


Well, it is safe to say that too much soy or proper but constant consumption of soy is bad for men. 

If you are the type of person who doesn't want to take risks, then ignoring soy protein for bodybuilding is the recommended way for you.

Since there are lots of scientific studies that say 'no' to soy outright when it comes to testosterone levels.

In case you are a vegetarian and concerned about protein intake, you can take soy while checking the amount consumed.

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  • Updated December 23, 2019
  • Foods
Yadhu Vijayakrishnan