Originally Posted by BarracksSi

+1 to what umd said. If the plan is to eat 1700 per day, then you exercise 1500 calories' worth (not impossible, even on a bike), your body's gonna freak out and edge into starvation mode. The muscles you've just worn out won't have any fuel to rebuild, so they're going to suffer, too.

If you think of it as net calories, then that's cool. The LoseIt app, for example, makes a baseline assumption of daily calorie usage, figuring that just spending time at the office and doing regular stuff will burn x amount of calories. If you eat only that much, but still exercise well, you'll hit a daily calorie deficit of up to a thousand calories at a time, and that's just not sustainable. Trust me, I've tried that, and it sucks.