Here is some info I found on Saw Palmetto:
The fatty acids in Saw Palmetto are thought to have Testosterone inhibiting effects on the prostate. Saw Palmetto also prevents testosterone from converting into dihydrotestosterone (DHT), which causes prostate cells to multiply, and also lead to male balking. Saw Palmetto herb prevents the binding of DHT to adrogen receptore, thus playing a key role in helping prevent and treat prostate enlargement, and also hair loss.