Cats cannot go on crash diets, or stop eating! Their liver's will start to fail. Any cat who has stopped eating for 3 days or more shoud be force-fed or put on an IV solution at the veterinarian. I have a diabetic, chronic renal failure, hyperthyroid apple-head siamese, 16 years old, and have learned much since the diabetes was diagnosed 5 years ago, the renal failure 1 year ago, the hyperthyroid in February this year.