How do I trim my weight...?

I am 6 feet tall and I weight 218 US pounds. I regularly ride both my road bike and my mountain bike to the tune of approx 120 miles per week. When I ride I ride with intensity, I'm not into checking out the scenery...My max HR is 175. It doesn't seem to matter what I do with my diet and exercise I just can't seem to shed the ton-age and it is driving me nutz. Please post any suggestions you feel are relevant. Thanks.

Steve,