This isn't so much controversial as it is a question of where you draw the line in simply granting a patient's request. Obesity is a disease, but it's a bit murky when you figure in lifestyle choices that contribute to it. Thus, it can have a strong psychological cause, underscoring the fact that it can't just be reprimanded and blamed on gluttony or sloth. It also can have a real genetic component. Such a patient erroneously believes it is simply between his or her doctor and him- or herself, which isn't true. In this case, evidence-based medicine comes to the rescue, and your interviewer just wants to know whether you'll treat this like the disease it is or merely like granting a favor.