You probably can’t stay on 500-600 calories a day without medication. One type of medication helps you stay on 500-600 calories a day, by blocking your appetite, so you are much less hungry. Another type of medication is used to decrease your carbohydrate cravings, so you aren’t as hungry for sweets and starches. A third type of medication helps limit fat storage and blocks hunger. Appetite suppressants (phetermine, phendimetrazine, diethylpropion, benzephetamine) are used to block hunger. Other prescription medications (Zonegran, Topemax, Naltrexone, Wellbutrin, Januvia, Janumet, Invokana) are used to block carbohydrate cravings. Injectible GLP1 and GLP1 analogs (Bydureon, Victoza, Symlin, Byetta) are used to help limit fat storage and block hunger.