Here's the deal: Yes, your metabolism affects your size, and the faster your personal motor runs, the more calories you'll burn. But the truth is, a slow metabolism isn't the real reason you're packing on pounds. You are the reason.
As a general rule, arrive at the airport no later than two hours before your domestic flight is scheduled to depart. This is somewhat later than the typical suggestion of three hours for an international flight.
The Transportation Security Administration agrees with it, but airlines don't. For instance, American Airlines advises passengers to be at the airport two hours before flight time for international departures and 90 minutes for domestic flights. Also, there's an exception for flights to certain overseas destinations, which require that you check in earlier.