Sometimes the answer to your question lies in the persons habits. I personally, traveled alot when i was in my 20's. I got to eat out at lots of different restaurants in Dallas, Austin, San Jose, Santa Cruz, Monterey, Milpitas, San Fran, Hudson Mass, Marlboro Mass, Boston, Chandler Arizona, Orlando, Santa Fe, etc. Most of the towns that have anything to do with semiconductors. I became a food connisseur (probably spelled wrong). Also, i got to know wines. These things take their toll on people. You begin to enjoy a good meal. Your taste buds become your hobby. You dont have time for anything else.
I can see where people like that get heavy, and it gets out of control. I just finished traveling about a year and a half ago. I can now start to work on my weight i gained in that time period. Before i got into this industry i was 6 foot 4 180 lbs. I couldnt put a pound on.
Then again, there are some people that are just sick, and they just eat to eat. I cant see where people would do that....