I think, here in America, which is such a thin-obsessed nation (in the media -- look at the vast majority of runway models after all) we should be careful with throwing around the word obese. This is so particularly for women.
This may sound like I'm being cute but I'm not. Is the woman obese or merely full-figured? Again, I'm not being cute. Take the full-figured models Crystal Renn and Kate Dillon, for example. Depending on whether or not one is afflicted with thin-obsession (or the degree to which one is afflicted by this), one or both of those women might actually be considered "fat."
Some people might think of Oprah as "fat." I don't. I think of her as pleasantly plump -- Oprah Winfrey, in my opinion, looks better with a few extra pounds (and curves!) on her than she does thin.
I was one of the few people, perhaps, who did not think she looked good that time many, many moons ago when she lost all that weight. If you're not old enough to remember, ask your mother or grandmother -- remember the time she came out with a wagon full of bacon fat (eighty pounds worth or so?) to show how much extra weight she was carrying? Remember that? I did not think she looked good.
The important thing is to be fit and healthy. Do not, I repeat, DO NOT obsess over the scale. Eat well and get exercise -- plenty of fruits and vegetables, nuts and grains (don't do any fancy schmancy diets that don't work anyway) and get plenty of exercise, which is easier to get than you might imagine.
Remember, a lot of officially thin people are unfit and unhealthy unlike, say, the full-figure models I mentioned before, Crystal Renn and Kate Dillon (those two are extremely HEALTHY from what I can tell).
Listen, good luck to you and don't obsess over numbers on a scale!