You need to determine if it is food related or if it reflects a medical problem. Provide your cat with nutritious food. Have you changed its food? Is the food too old? Is your cat getting food elsewhere? Rodents, neighbors, your kids? Is there clean, fresh water? Have you changed anything about where they eat? Smaller portions throughout the day may help. Female cats in heat will naturally go off their food somewhat. However, your cat may have a health problem that you need to address immediately, hairballs are affecting the digestive tract, anorexia, skin problems, kidney disease, parasites, bacteria, dental problems, tumors or infections. There is a more rare problem, Pica, where cats eat non-food items, which is thought to be from boredom. Remove non-food items and provide some new toys or play things.