Actually, the calorie theories: 1) 3,500 calories equals a pound, and 2) that you must burn more than you eat, are pretty much old school and no longer the leading theories for causes of obesity or even weight.
New theories that have replaced these old myths are theories of set point weight (your body has a pre-determined natural weight) and theories about the number of fat cells each individual has--fat cells are created around puberty and the quantity usually doesn't increase overtime, but the size of individual cells expand and contract. This theory suggests that some individuals have larger quantities of fat cells and therefore, can only lose so much weight before hitting a natural plateau--the cells may have shrunken as much as possible, but the quantity of cells doesn't decrease.
Knowing this information, you can improve your health and body appearance quite significantly with exercise and with eating correctly. It's not as much about how much you eat as it is about the timing, quantity and makeup of your meals. It's much better to eat high quality (whole, unprocessed foods), balanced (proper ratios of protein, carbohydrates, and good fats), and frequent smaller sized meals than worrying about attempting to reduce calories by 500 per day or whatever your goal weight loss may require. Additionally, by combining this type of eating with regular exercise, you'll increase your metabolism and burn more calories throughout the day.
When you read that exercise doesn't help you lose weight, you may be reading that muscle weighs more than fat, and therefore, on the scale, you will be heavier if you build muscle. In reality, this is somewhat true. Yes, muscle is denser than fat, but you aren't going to gain a ton of weight by replacing your existing fat with muscle. The beauty of this is that even at the exact same weight, let's say 125 lbs, someone with lots of fat is visibly larger than someone of the exact same weight with lots of muscle instead of fat.
Putting all of this together, by exercising and eating correctly (frequent, balanced, and high quality whole foods) you can lose fat which is much better than just losing weight, and as a bonus, you'll replace some of that fat with muscle. With the added muscle, you'll naturally boost your metabolism on an ongoing basis.
The Straight Scoop about Dieting, and