I used to believe what you're saying, but my interactions with obese patients in a medical setting has led me to think otherwise. A lot of obese patients are afraid of going to the doctor's office or hospital because they don't want to be criticized or shamed for their lifestyle choices by a person who's been thin and healthy his entire life. I suspect that many obese patients would be deeply comforted to hear something like, "Trust me, I know that weight loss is challenging because I'm struggling with my weight right now, too. But hopefully with a lot of work, we'll both reach our goals. Here's what I've been doing so far: blah blah blah blah." If presented in the right way, the weight loss talk wouldn't have to be hypocritical at all. In fact, it could actually serve to be quite comforting and empowering for a patient who's terrified of being judged and embarrassed.
I've come to believe that being an overweight (or formerly overweight) physician could actually serve as an asset, in that it would allow one to be better able to relate to the large segment of the American patient population that struggles with obesity. The same reasoning applies to smoker or ex-smoker physicians, who can better empathize with a patient who's struggling to quit smoking.