Another part of it, according to the journal Science, is the fact that these people seem to get lots of exercise, whether they know it or not.
The secret, according to the Mayo Clinic, is NEAT, which stands for "non-exercise activity thermogenesis." The people who can ingest all those extra calories actually do burn it off. But instead of obvious exercise, they do it by fidgeting, changing position and lots of little motions that wind up using a lot of extra calories over the course of a day. - (HealthDayNews)