HappyJBH:
I would recommend a high carb diet. Breads, Pastas, Rice and good cheese, beans too. Engery dense foods are good for healthy packing on pounds, If your afraid of diabetes then avoid over doing it on sugar, also keep saturated fats to a minimum. Sea food contains healthy fats and oils. Just good, filling wholesome is the best way I think.
I agree with all of this, the only thing I would add is to watch out for excessive salt as well. This is what I am cutting back on now to get my blood pressure under control.
Fivehundred's points are worth considering, too. My wife was a BBW when we first met, and it was health-related circumstances that resulted in her need to exercise more and keep her weight down. For whatever genetic reason, my body is better suited to carrying extra weight than hers.