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.
Add another 30 to 60 minutes for an international departure leaving at a peak time. It's better to arrive at the gate early and catch up on your reading, than to arrive on time and miss your flight (most carriers secure the plane doors five minutes before departure time!).