Ever notice the color-coded exercise "zones" listed on cardio machines? There's a "fat burning" zone, an "endurance training" zone, and so forth. The colors look nice, but how many times have you chosen the "fat burning" zone and watched as your fat stayed put? That's because fat-burning programs keep you at a lower intensity level, when to lose weight you really need to burn big calories. That only happens when you exercise at a higher-intensity level.
Let's look at the math. In a half hour of low-intensity exercise, you might burn 100 calories. Of those 100 calories, roughly 80 percent will be fat calories, meaning that you've burned 80 fat calories. In a half hour of high-intensity exercise, you might burn 300 calories. Of those 300 calories, roughly 33 percent will be fat calories, meaning that you've burned around 100 fat calories.
Get it? Even though the percentage of fat calories burned is higher during a low-intensity workout, you're burning so many more total calories during a high-intensity workout that, percentages aside, you are still burning more fat calories — not to mention the 200 additional carb calories.