I was once a genius but now my mind is dull. What can I do to jump start my brain again?

Maybe it was the Prozac? I know that particular medication affects the sex-drive, anyway. May I ask if you've gained a lot of weight since you were a child? Because there have been studies done in the past year that show that overweight people are consistently more mentally dull than a physically fit person of the same age. I've found this to be true for myself; as since I began my diet and excercise regimen a month ago, concentrating and executing tasks is *so* much easier than before.