DG,
If you have a fatpad in the pubic area, of course if it is lost, you'll "gain" that 1/2 inch...or more. It depends on how much fat is there.
Having said this, if you have a huge ass and lose it, it doesn't mean your dick will grow. With me, my stomach and pubic area was huge with copious amounts of fat. When I lost all of it, my penis appeared to have grown, when in actuality, it was there all along, just hidden by all of that fat. Basically, the afterwards is just an optical illusion. It does, however, make me feel great to know that I am like the other males in my family.
Diet: I did mine through surgery- Lap-Band. Any SENSIBLE diet and exercise plan will work, though. But, BE PATIENT!