Butter is very high in fat and can cause a cat’s intestinal tract and pancreas to become inflamed, which can lead to gastroenteritis and pancreatitis. Some cats will develop vomiting and diarrhea, which is generally mild. But for those that develop pancreatitis, the condition can be much more significant. They can experience more severe vomiting and diarrhea, along with abdominal pain, decreased appetite, and weight loss.