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.
Dulles recommends arriving at the airport 2 1/2 to 3 hours before departure time for an international flight. I tend to leave myself 2 1/2 hours if my airline has allowed me to check in on-line, because then I only have to queue in the shorter, faster line to check my luggage and get my passport vetted.