Heather-
Weight gain always promotes increased metabolism, with both fat mass and muscle mass contributing to your BMR (muscle contributes more, but fat does to). Contrary to popular myths, obese people tend to burn more calories a day than thin people. That’s why it’s much easier to lose weight quickly when you’re 500 pounds than when you’re trying to lose that last 10 pounds. In your first post, you ask why overweight, unhealthy Americans haven’t reached metabolic perfection, even though they consume so many calories. The truth is, they do burn a lot of calories every day, just not enough to compensate for their huge intake.
If you want your body to burn calories, you have to do something to force it to. If you want to eat like Michael Phelps, then work out like Michael Phelps. I think that eating a lot every day has its advantages, and I like to eat a lot, but you have to exercise if you don’t want those extra calories to turn into fat.