Obesity really is a chronic problem . . . and as such it seems like it would be best treated and studied by internists and endocrinologists. I guess you could focus your research on how obesity affects the management and treatment of people with acute problems. I think it also depends on what kind of research you want to do. If you are thinking about clinical studies where you are trying to see if an intervention will help people lose weight then I think that really is IM. But if you are thinking about cellular level basic science research, then that doesn't really "fit" within any particular specialties' domain, and maybe you could be one of those people who does 1/2 time ED and 1/2 time basic science research. I think you should ask yourself, "if I had to do one or the other," and of the answer is EM then do EM and the research will figure itself out. If the answer is obesity research then I think you should look strongly at IM.