I understand those reasons, but I'll say that calorie restriction by itself can leave the body undernourished, especially on exercise days.

I used the LoseIt! app mentioned earlier religiously for six months and cut thirty pounds without feeling like I was starving. It recommends fewer calories as you get lighter, so my intake allowance has dropped from nearly 2000 down to the mid-1700's now. But, it "credits" (for lack of a better term) calories for the exercise you're doing -- so if you do about 700 calories' worth in a workout, you can add another 700 to your food for the day. It's got a big selection of common physical activities, and it counts the calories for each session depending on time and your body (age, gender, and weight). If you don't work out that day, you just don't eat as much.

The result is that I'd eat an average of 2500 calories or so on exercise days. I've seen guys try to stick with 1500-calorie diets plus working out and they have a hell of a time because they feel so starved. I try to tell them later that they're just wrecking themselves -- their bodies are actually trying to operate on only a few hundred calories a day, which is all that's left over after burning energy for all that exercising. They don't get in any better shape, and they don't gain any more strength or endurance.

The app focuses on calories, so you run the risk of still being badly nourished if you continue eating the wrong stuff in smaller amounts. But, read between the lines, and you realize that you can either have a couple bags of chips, a Snickers bar, and a Gatorade to fill your daily budget, or you can have full meals of veggies, fruits, and some lean meat for the same amount of calories.

Still, when it comes down to it, calories are calories, and if your body doesn't get enough from food, it gets them from stored fat. Good foods help you gain strength and cut fat a lot quicker.