Daily visits to the gym and aerobics. A strict diet which includes no fat or desert. They will only eat once in the morning, once in the afternoon and once in the evening of strictly healthy dishes.
Plus they have to be in trim condition with modeling experience to get a job unless they are 2nd generation or a big name like Kong. And then if Natalya or Tamina were to let themselves go, they'd be letting themselves straight out the door.