Fasting is the act of purposefully withholding food and, in some cases fluids, from a pet for a period of time. Contrast fasting with inappetance, which is a situation in which the pet sometimes won’t eat or won’t eat as much as it needs.
Fasting from food and sometimes from fluids often is required for certain blood tests  and for procedures involving general anesthesia, such as dental procedures. Fasting is also part of the treatment method for pancreatitis.
Fasting, like inappetance, can be difficult on a diabetic pet. The nature of the difficulty depends on the length and nature (food only or both food and fluids) of the fast. When withholding food, you may need to adjust insulin dosage or forego an insulin shot. Withholding fluids (including fluids available to your pet in wet food) can elevate certain blood values. Consult with your veterinarian about the need for and potential effects of fasting on a diabetic pet.
The term fasting is also used to describe blood glucose readings taken before a meal. This is when blood glucose should be at a lower point because of the lack of food for a number of hours.