Loss of appetite in cats can range from minor to serious. Common causes include picky eating, switching food too quickly, oral pain, or underlying conditions affecting digestive health for cats such as gastroenteritis or kidney disease. For occasional, mild appetite dips in an otherwise normal cat, try gently warming food to boost its aroma. If your cat refuses to eat for more than 24 to 48 hours, or shows vomiting, lethargy, or weight loss alongside poor appetite, consult a vet promptly to rule out underlying illness.