One paper suggests that there is a dopamine response difference in the obese: http://www.ncbi.nlm.nih.gov/pubmed/11210998
The causal direction is open to interpretation, but I still think that there is a difference between 'overweight' and 'obese'
this probably plays a part in it for some, but only a small part if I would have to guess, there's way more to it.
First sign there's much more going on than just 'a disease' is the fact there are way more obese people in the US for instance than in most other countries. And also for instance that children where both parents are obese are more likely to develop obesity as well. First comes down to culture, second to lifestyle. Not two things I'd directly associate with words like 'genetic or 'disease'.
You're not condemned to be obese if your genetics give you the propensity for it, but it's also fair to say that the genetics mean that disease-like interventions are necessary. http://www.hsph.harvard.edu/obesity-prevention-source/obesit...