Simple Causes
Causes for low body weight can be simple. Say, your high-energy cat is a finicky eater. If he spends his days running, playing and jumping rather than snoozing, increasing his portions and the frequency of his meals can pack the pounds back on. If you've just found a cat and he's emaciated, chances are good that he's just hungry, and fixing the problem may be as easy as feeding him -- after having a veterinarian check him for diseases, of course.