Yup, I've put on weight during my PhD too... a fact which I manage to ignore until the rare occasion that I have to go somewhere smart and my clothes from a year ago don't fit properly. Sigh. I don't exercise enough, but because I never have in the past either, I'm certain it's the snacking that's the underlying cause. Recently, I've started avoiding sugar and fat and have lost a couple of pounds, so what I'd say is try to avoid those high calarie foods. Also, I've had to face the fact that it's going to take a bit of time to shift the extra weight. Not unlike the PhD actually, in that no matter how much you'd like to, you can't do it over night. I felt better once I'd accepted that.