Isn't soy protein bad for men?

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Soy contains isoflavones, which are structurally similar to the main estrogen in men. This fact has raised the worry that consuming soy could have adverse effects on male sexual health; however, the best available evidence indicates that consuming soy does not affect male reproductive hormones.

Phytoestrogens are plant compounds structurally similar to estradiol, the main estrogen in men and premenopausal women. Because soy contains isoflavones, a type of phytoestrogen, concern has been raised about the possible effects of soy on men’s health.

Thus far, two case reports have documented adverse effects such as gynecomastia, hypogonadism, reduced libido, and erectile-dysfunction from an estimated 360 mg of soy isoflavones per day for 6–12 months. However, a meta-analysis of 15 randomized controlled trials (RCTs, a much higher level of evidence than case reports) found that men’s levels of total and free testosterone were not notably affected by either 60–240 mg of isoflavones or 10–70 grams of soy protein per day.

Accordingly, a couple of scoops of soy protein powder are unlikely to have estrogenic effects in men. If you’d like to take more, however, look for a soy protein concentrate or isolate produced through the alcohol wash method, which dramatically lowers the isoflavone content.[1]

Keep in mind that the isoflavone content of different soy products can vary depending on several factors such as the variety of soybeans used, differences in growing and storage conditions, and different food-processing techniques.[2] You can see how it varies below.

Isoflavone content of common soy foods


Reference: USDA FoodData Central Databases. Accessed Jan 18, 2019