The key

There are five groups of reasons that cause overeating:

1. willful overeating, as in Newfie,   I wants________.
2. physical causes
3. environment and tempations
4. maladaptive behavior
5. food addiction

for more details on the last 4 see http://philosophyofweightmanagement.blogspot.ca/2014/07/expansion-of-lettuce-effect.html