Well you can't shift body fat. Some people carry it in different places than others. Diet and training is key to get rid of body fat. If you're fairly low body fat already, then you'll have to diet ultra hardcore to get it gone. Sit-ups alone just won't help you with that. Some people respond to cardio, others don't in the same way.. I'm the type that can lift and diet, but don't need tons of cardio to lose the fat. If my diet isn't dead on, it doesn't matter how much cardio I do, I'll still hold fat. Everyone is programed a bit differently that way. You just have to figure out what combination of diet, cardio, lifting your body responds best to.