With an alarming number of fat cats out there -- one scientific study concluded that 53 percent of cats in the U.S. are either overweight or obese -- your not-quite-svelte feline may need to quit the clean plate club. Tubby tabbies face an array of possible health problems, including arthritis, diabetes, heart and liver issues. They may also suffer illnesses, such as bladder stones or skin conditions that require special eating habits. And diabetic cats need strictly monitored care and feeding. But getting a cat to follow any diet not of his own choosing isn't as simple as cutting out treats and serving tiny portions. Knowing what to expect as you alter your cat's meal plan will help you to keep him on the right nutritional path.

When should a plump cat slim down? Most vets classify a cat with more than 20 percent body fat as overweight, but more simply, if the feline profile viewed from above has no waistline or abdominal tuck, the cat is too fat. You should be able to feel, but not see, his ribs. He shouldn't have folds of swinging fat when he walks. A cat's ideal weight depends on age, breed, lifestyle, bone structure and gender, but the average adult cat generally tips the scales at 7 to 11 pounds (3.1 to 4.9 kilograms), with females weighing less.

Two to 3 extra pounds (.9 to 1.36 kilograms) for a cat is equivalent to 40 pounds (18 kilograms) for a human! No wonder we have such an epidemic of obesity. Furthermore, cats that have been spayed or neutered use fewer calories than intact felines, so they often don't need to eat as much; they put on pounds because their owners offer too much food and not enough exercise. Never put your cat on a diet, or switch to "diet food," without first consulting your vet. Drastically changing the amount or type of food your cat eats can invite digestive problems or deplete crucial nutrients. The vet will determine if your cat has health problems in addition to being overweight. She'll then suggest the right food to attack the problems, or an eating regimen, including portion sizes, to tackle weight loss.