I think they should diet to get to a lower body weight first, and then hit the gym.  I think they need to understand how calories in/calories out work before they try to factor in exercise -- so many obeasts go to the gym then go home and order their regular first pizza and a second one as a reward.  They totally negate their calorie burn, and probably make it worse.  Diet is so much more important than exercise in weight management -- it's a basic they need to get down first before they should do the exercise.