The general accept is that obesity is genetic. But the combination of obesity and its stability almost always equates increased questions related to ways to maintain a normal weight.

Stable obesity:
When one is stable at a "set point" more then 20 lbs (more or less) above what is considered ideal for ones height and weight and finds it hard to lose (or gain, but who complains about that) away from that "set point". It is my opinion (and everybody's got one :) that many of these people would be better off where they are at then going to war with their bodies and screwing up their metabolisms.

If a stable obese person wants to lose weight he should attack it primarily from the exercise end of the spectrum. Even if that doesn't work he will still be more fit and healthy in the long run.

Unstable obesity:
When one doesn't seem to have a "set point" and slowly gains weight over time. This is a genuine metabolic disorder and it may be caused by disease, genetics, or simply by a long history of eating when one is not really hungry (comfort eating) and/or a sedentary lifestyle.

Whatever the cause, it should be treated like a disease and not a "character flaw". The weight needs to bought down before he gets so fat that it interferes with his mobility.