"One of the biggest health myths that needs debunking is that soy is a health food," says Kaayla T. Daniel, PhD, CCN, author of The Whole Soy Story: The Dark Side of America's Favorite Health Food. "In Asia soy's well known for its ability to tank the libido.
Zen monks use soy as an aide to celibacy and Japanese wives serve extra helpings of tofu to unfaithful husbands to kill the ability, the desire," says Daniel. The science behind that is all soybeans contain phytoestrogens known as isoflavones. "These plant estrogens aren't identical to mammalian estrogens but they are close enough to interfere with the production and utilization of testosterone in the body," Daniel says.
Some studies have shown it may contribute to reducing a man’s libido. The occasional tofu dinner wouldn't have much of an effect on sex life, but if vegetarian or vegan man chooses soy-based protein over other plant based proteins on a regular basis, it may make a difference. "Researchers have proposed that the estrogenic properties (that is, those that emulate the female sex hormone estrogen) of soy's isoflavones can cause testosterone levels, along with sexual desire, to drop," says Ficek.
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