The truth about abs is that you have a layer of fat between the skin and the muscle, and it doesn’t matter how many crunches you do, if you don’t cut down that layer of fat, you’ll never see your abs. You have to do exercises that are high in caloric expenditures — compound joint movements like squats, lunges, lower body exercises that recruit a lot of muscle fibers because they’re incorporating more than one muscle group. The overall result is that you burn more calories.
There is no such thing as spot reduction. You’re not going to lose fat in your midsection if all you’re doing is crunches. Crunches burn very few calories compared with other things you can do.