While I think that diet is the more important of the two, neither will work without the other. To get into good shape, one must have healthy eating habits that supply the body with enough nutrition to power the body, but not flood it with excess calories. One must also exercise all of the muscles, but not overdo it. It is a hard balancing act that takes a full lifestyle change, and anything less will only lead to failure. I am able to say this because it is a balance that I am still trying to strike. I have lost quite a bit of weight and gotten in better shape, but I am not all of the way there yet. I still have slip ups in the kitchen, and occasionally skip an exercise when I know that I should not.