straight from the write up.
[i] resveratrol acts as a potent estrogen antagonist (while also acting as an agonist in some tissues, similar to the drugs clomiphene and tamoxifen).
In higher concentrations, it acts as an aromatase inhibitor. That means that it stops the body from whittling away at your Testosterone.
This is cool because if a substance stops Testosterone from being converted to estrogen or estradiol, it not only prevents the nasty effects of estrogen (loss of muscle and strength and accrual of body fat), but it increases your level of Testosterone, leading to additional strength and muscle! [/i]