Many people believe you can "target" fat loss through certain exercises, such as crunches for belly fat. The truth, however, is that no number of crunches or sit-ups will give you a six pack.
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A 2011 study from the Journal of Strength and Conditioning Research measured the impact of six weeks of ab exercises on abdominal fat loss. While exercise performance improved, there was no significant reduction in abdominal fat. This corroborated a few other studies that suggest that spot reduction is a myth. You can't pick and choose where you lose fat; you just have to work on losing fat overall.
This isn't to say strength training isn't helpful, of course. Abdominal exercises will certainly strengthen your core muscles, but a six pack only becomes visible by reducing your body fat to lower ranges (about 10% for men and 20% for women). Crunches do nothing to help you with this goal.
(It's worth noting that some research does support the existence of spot reduction, but in very trivial amounts. One study shows that the breakdown of fat (or lipolysis) increases in fat cells adjacent to contracting muscles -- but only about 0.1g of fat per 30 minutes of exercise. That's the equivalent of 0.0008 tablespoons of butter.)
Knowing that "spot reduction" is a myth, the only thing that you can do is continually lose body fat in the correct manner. Your current leanness, not the exercises that you're doing, dictates the area of the body where fat loss occurs. Be patient, and you'll eventually see fat loss in your desired areas.