I lost 10 lbs last year from just riding, and I did a hell of a lot of it.

This year I learned about nutrition through a variety of sources, but if you want one book that puts it all together for you start with "Eat to Live" by Dr. Joel Fuhrman. I'm just over 6' started the year at 230 lbs and got to 180 lbs in less than six months.

There's a lot of good advice written above (though I'd be skeptical of any magical pill or powder that proports to make the weight vanish). I'm not the type to keep track of points or count calories, and I'm not about to go hungry by portion control. I've also done about 1/2 the amount of riding this year that I did last year. If you're still in high school you might ask yourself just how much time you want to be on your bike. Dedication is a great thing, but I wouldn't have given up the time spent in high school, doing stupid teenage high school things, for anything in the world...