Cat excessive hunger My male part Siamese cat is ALWAYS hungry (for last 5 months).I switched to Hill's I/D (from W/D), plus dry W/D. Still constant hunger. Vet says blood panel and 2 ex-rays showed normal. Could it be parasites?
Thank you!

Has he an any weightloss?
If his hunger is accompanied by thirst, and frequent urination you should have him tested for diabetes. Very common in male cats. This isn't a death sentence, its easily managed and cats can live for many years with the condition, and unlike humans, can "grow out of the disease" once their body weight is stabilised for a period.

Glucose is usually one of the panels in most bloodworks run.

Did they check your cats thyroid?

Why is your cat on an expensive prescription diet? W/D is for weight loss and I/D for liver problems. If there's nothing wrong with him, why does the vet feel it's necessary for him to eat some "special" diet.

Not to mention that these diets are inferior in quality. Speaking of diabetes, the high carb level in Hills can CAUSE it. This is the first ingredients of the canned I/D:
Water, Pork Liver, Egg Product, Corn Gluten Meal, Rice Flour, Pasta Product, Soybean Oil

Does this sound like mice, chickmunks, birds and rabbits to you?

Is he underweight?