The Permanence of Fat
That's the obvious inference from the research dug up by Gina Kolata in her new book. If you're genetically predisposed to being chubby, you have two choices: stay chubby or feel like you're starving for the rest of your life. Money quote from an article in Science in 2000:
"Those who doubt the power of basic drives, however, might note that although one can hold one’s breath, this conscious act is soon overcome by the compulsion to breathe. The feeling of hunger is intense and, if not as potent as the drive to breathe, is probably no less powerful than the drive to drink when one is thirsty. This is the feeling the obese must resist after they have lost a significant amount of weight."