Perhaps, just perhaps, now this is a crazy idea, but perhaps all that nutritional advice is a) wrong and b) falling on deaf ears.
In my personal experience people (other people not me of course) are overweight because they are not active enough and eat too much. Portion sizes are too large and snacks at 9pm are dangerous.
Now a small percentage of the population does have a hormone problem, slow metabolism, big bones or whatever. I believe they could solve the majority of their problems by getting off the sofa and reducing portions and kill the snacks. Drink some tea and move. Increasing muscle mass is far better for weight control than simply doing more aerobic exercise.