It may be (there's some evidence for the belief but, who knows?) that it doesn't matter one wit what you think you're burning so don't even bother counting that toward you daily caloric requirement. For sure though, you can swing 4-5 pounds in a day just losing water weight so 2.5 lbs could even mean you lost a pound. At least in my experience, unless you actually weigh the food you eat (like Lance Armstrong did), you can be off quite a bit-- e.g., how much were those nachos, really: 1-serving... 450? Or, perhaps, 1,250?