it would only benefit themselves to be honest so where's the incentive?  I hypothesize it's because they get to look like the victim. They tell people they can't lose weight no matter how little they eat and blame their metabolism because it removes responsibility. They say it so people will know that they aren't fat because they're lazy, gluttonous, and undisciplined; they work really hard on their diet but it's their genetix that prevent the weight loss. If they ate any less, they would go into starvashun mode and get even fatter, so obviously they can't just "eat less". Also they love playing the victim, for some reason. (Just in case it wasn't clear, the excuses above were written from a fatty's POV - they probably believe their own bullshit, I don't)