You have to use a combination of dietary adjustments and exercise (doesn't have to be hardcore) to boost your metabolism.
This week's "dietary adjustment" for me was taking the scenic route to turn the .75 mile to the cafe into a 19.5 mile bike ride through the countryside, with four rather unkind hills.
Felt pretty good, too; as best I can recall, it's the first time I've done that much distance with a moderate load, (about 10lbs; it's really as much about the drag and crosswind area of the panniers as the weight, up to a point) without climbing off the bike at any point, and with only a brief stop to turn on the taillight and switch water bottles. If I can get to the point of doing that three times in a day, sleeping in the hammock and not being too sore to do it again the next day, I'm going to have to plan a serious tour.