Like humans, dogs and cats can develop diabetes. As a quick refresher, diabetic animals don’t produce enough insulin to drive glucose (sugar) into the cells of their body. The body thinks it is starving, so the animal tries to eat more and more food. Muscle starts to break down so the protein can be used as energy, as it does with starvation, and the animal loses weight and muscle mass. All the glucose that is present in the blood goes through the kidney, which filters it out. Glucose pulls water with it into the kidney, so the animal drinks a lot and urinates a lot. Those are the hallmark signs of diabetes: increased drinking, increased urination, increased appetite and weight loss.
Other diseases can cause similar clinical signs, so if you notice any changes in your pets drinking, appetite, urination, or weight, you should schedule a physical exam and do bloodwork and a urinalysis to figure out why.