Recently some so called experts have claimed that eating soy can affect the testosterone level in negative way in man. Soy contain Phytoestrogens which do interact with our testosterone. Our Androgen and Estrogen both contain receptors that interacts with soy.
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Soy when interact with estrogen receptor it increases the testosterone level while when it reacts with androgen it decreases the testosterone level. If we eat soy once in a while than these imposed affects will vanish quickly. Even if one eat soy only once a day there will be temporary changes in the Testosterone level. So it is not correct to say that Soy kill our testosterone level.