Fasting has a place in the pantheon of many religions as well as being a standard way of performing sacrifice in many cultures. Yom Kippur, one of the holiest days in the Jewish religious calendar includes fasting as part of ritual of atonement—observant Jews fast from sundown on one day to sundown the next. And Muslims celebrate the month-long holiday of Ramadan with pre-dawn to sunset fasts. Some groups also use fasting as a method of spiritual and/or bodily cleansing.
Fasting for people who have diabetes is a tricky area that brings the desires and wishes of the person contemplating the fast in conflict with the need to consume adequate nutrition in order to avoid the complications of blood glucose excursions in either direction. The level of risk associated with fasting depends on diabetes type, control level, medication regimen, and current physical condition.
In general, risk level is low in those whose diabetes is controlled through dietary means alone or with oral agents that do not stimulate insulin secretion from the pancreas. It increases for those on oral medications that promote insulin secretion, becoming highest for those with type 1 diabetes.
The risks associated with fasting are related to the subversion of normal physiological processes in people with diabetes. When people without diabetes fast, glucose levels are depressed, which reduces the amount of circulating insulin. Simultaneously, levels of glucagon and epinephrine rise, which releases glucose from liver glycogen. If fasting continues beyond a few hours, glycogen stores become depleted and fatty acids are released from the fat cells to be oxidized into ketones. The skeletal muscle and several organs will burn ketones for energy, thereby sparing available glucose for use by the brain.
In patients with type 1 diabetes, life-long recurrent episodes of hypoglycemia and autonomic neuropathy may blunt the normal response to fasting. When people are hypoglycemic repeatedly the body isn’t able to replenish glucogen stores adequately. In the face of inadequate reserves of glucogen the liver can’t secrete glucose to prevent hypoglycemia. Furthermore during fasting, patients with type 1 still require some level of basal insulin. Patients may not realize the need for insulin and omit coverage. Prolonged fasting in the face of insulin deficiency can lead to a situation where the brain is deprived of glucose because there isn’t sufficient insulin available to move glucose from the bloodstream into the cells. This stimulates the overproduction of ketone bodies and ultimately ketoacidosis, a potentially fatal situation.
In patients with type 2 diabetes alternations in insulin and glucagon response are not as dramatic and the development of ketoacidosis is not usually a concern. However, hyperglycemia can be as significant problem as can hypoglycemia. In patients with type 2 diabetes the liver often over secretes glucose in the fasting state leading to the hyperglycemic condition called the Dawn phenomenon.
Most religions do not obligate people who are ill to fast. In fact the opposite is true; fasting is usually actively discouraged. Yet, people with diabetes may not consider their condition a manifestation of acute illness, or they may feel the spiritual benefits of fasting outweigh the risk.
All people with diabetes who are contemplating fasting should
- Discuss their intention with their medical team
- Be in good physical condition and well hydrated
- Check their blood glucose frequently during the fast
- Have insulin (if taking insulin) and fast-acting carbohydrate available for low and high blood glucose
- Stop the fast if hypoglycemia results or if hyperglycemia above 250mg/dl with ketones occurs.
*Episodic fasting as a method of weight loss is usually ineffective and not a recommended choice.