The thinness of cats can be a source of disease. Simple nutrition will not fix the problem. The solution is special finished feed. In this article you will learn how to feed a cat for weight gain. Content Lack of weight in cats can be caused by physiological reasons or any pathology. Causes of thinness can be: starvation; stress metabolic disease; malnutrition; feeding a large number of kittens; dehydration due to disorders of the gastrointestinal tract (vomiting, diarrhea); infection with worms (helminths).