Donna Simpson currently weighs 600 pounds, so she's going on a diet in hopes of reaching what she considers her ideal weight: 1,000 pounds. The 42-year-old mother, a resident of Old Bridge, NJ, consumes a whopping 12,000 calories a day in an effort to reach her goal. Simpson already holds the Guinness World Record for world's fattest mother. She insists she's healthy despite the fact that she…