Illness
Cats that suffer from hypothyroidism gain weight, become lethargic and have dull coats. Your kitty's thyroid gland controls his metabolism through the production of hormones; an impairment of the thyroid gland reduces these hormones, resulting in a slowing of the metabolism and therefore weight gain. Feline hyperadrenocorticism or Cushing's disease can also lead to weight gain due to increase in the production of cortisol by the adrenal glands. This condition results from a tumor or the continued use of corticosteroids to treat another illness can result in Cushing's disease. In addition, several other health issues, such as an intestinal disease or diabetes can also cause weight gain. To properly diagnose and treat your cat, bring him to a veterinarian for an exam. Plus, your vet can give you some tips on weight loss if your cat receives a clean bill of health.