Yeah I've been losing weight recently, and a 5k Run burns about 500-600 calories for someone my size. That's a shit load of effort, and not something an overweight person is likely able to do every day. But 600 calories is like a single big mac (just the burger). There's only so many calories you can reasonably burn in a day, but there's practically no limit to how many you can eat (none that you're likely to find without making yourself sick at least)