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Recommendations for Insulin Using Patients When Fasting

Mar 11, 2017

Can patients who use insulin safely fast?

The topic of fasting comes up often as patients may have to fast for laboratory tests, surgery, diagnostic procedures (e.g. colonoscopy), or religious reasons, or just to improve their blood sugars or lose weight. It can be a major challenge for just about anyone but can be particularly difficult for patients with insulin-dependent diabetes.

Patients with insulin-dependent diabetes need to understand the management of diabetes during fasting to prevent hypoglycemia (blood glucose < 70 mg/mL or 3.9 mmol/L). Plus, the duration of the fast affects how much insulin is needed during that time.

The management of people with diabetes who fast is mostly based on expert opinion rather than medical evidence gained from clinical studies.

For patients using insulin who want to fast, there may need to be extra attention since healthcare professionals (HCPs) who are not experienced in dealing with fasting people with diabetes might not consult or even be aware of published recommendations [4]. Evidence-based guidelines are important and, although the evidence available in this area continues to increase, more randomized controlled trials are needed to fully answer questions related to controlling blood sugars when fasting.

One of the best examples of large numbers of people fasting is for Muslims during Ramadan, who fast from 15 to 30 days.[7]  People with T1DM will be advised not to fast because of the risks of severe complications.

However, recent studies involving young adults suggest that if the patient is stable, otherwise healthy, has good hypoglycemic awareness and complies with their individualized management plan under medical supervision, then many of these patients can fast safely. One study involving 33 adolescent children with T1DM found that 60.6% completed the fast without any serious problems [5]. These children and their caregivers were given intensive training and education on insulin adjustment, SMBG, and nutrition before Ramadan and were closely monitored during the monthlong fast. In total, five cases of mild hypoglycemia and no cases of DKA were recorded [5]. Another study involving 21 adolescents with T1DM also found that a majority (76%) could fast for at least 25 days [6]. However, the use of continuous glucose monitoring equipment in this study demonstrated that blood glucose levels fluctuated and some episodes of hypoglycemia went unrecognized, suggesting that regular SMBG during fasting is vital. The findings also highlighted the importance of thorough attention to hypoglycemia unawareness in these circumstances [6].  While the results of these studies are encouraging, they cannot be generalized to all people with T1DM. Strategies to ensure safety of individuals with T1DM who choose to fast include: Ramadan-focused medical education, pre-Ramadan medical assessment, including robust assessment of hypoglycemia awareness, following a healthy diet and physical activity pattern, modification of insulin regimen, and frequent SMBG or continuous glucose monitoring.

Not eating for an extended period of time leads to decreased blood glucose in all patients. In patients without diabetes, insulin levels decrease as glucagon increases, and the act of glycogenolysis provides about 75% of glucose requirements.[1] This mechanism allows blood glucose levels to remain within a normal range. In patients with insulin-dependent diabetes, the glucagon response is lost, and epinephrine becomes the main method to increase gluconeogenesis in the liver. However, the epinephrine response also diminishes over time; thus, patients with insulin-dependent diabetes are at risk for hypoglycemia.[2] Symptoms of hypoglycemia include sweating, shaking, mood changes, hunger, headache, tachycardia, and, in severe cases, unconsciousness, seizures, and coma.[2] Healthcare professionals should discuss the symptoms of hypoglycemia with patients who are planning to fast.

The duration of the fast and the type of insulin used can help guide insulin treatment during the fasting period. Some minor adjustments to insulin may be required if patients are fasting for laboratory tests or surgery (eg, 8-12 hours). Short-acting insulin before meals should be stopped until the patient has a meal. The basal insulin dose may need to be reduced by one half or one third, particularly for morning dosage regimens. Patients should be advised to eat a meal or snack and to resume their normal insulin regimen following the laboratory tests or procedure.

If possible, laboratory tests, surgery, or diagnostic procedures should be scheduled for the early morning because fasting until later in the day will cause greater glucose level disruption.[3]

Colonoscopies require more planning for patients with insulin-dependent diabetes because the fast includes specific dietary orders and bowel cleansing. Colonoscopies should also be scheduled for early in the day to cause the least disruption to blood glucose levels. On the day before the procedure, patients are asked to follow a clear liquid diet. Blood glucose should be checked throughout the day to monitor for hypoglycemia and hyperglycemia. Adequate hydration on the preoperative day is important for cleansing the bowel and preventing dehydration, which can lead to hyperglycemia and possibly ketoacidosis. On the day of the colonoscopy, patients using intermediate- or long-acting insulin should be advised to take one third to one half of their insulin dose. Mealtime insulin should not be used until the patient eats. Fast-acting insulin can be used to correct hyperglycemia.[8]

Fasting holidays present a unique challenge. Both Judaism and Islam exempt people with medical conditions that contraindicate fasting. Patients with poorly controlled diabetes or patients who are pregnant should be advised against fasting. Blood glucose monitoring is absolutely essential when fasting; if hypoglycemia develops, the fast should be broken and the low blood sugar corrected.

Suggested adjustments to insulin regimens based on the duration of the fast is outlined in the table below.[3,6,7]

Table. Recommendations for Insulin Regimens During Fasting[1,2,3]

Duration of Fasting Type of Insulin Used Recommendation
Sunrise to sundown Long- or intermediate-acting (glargine, detemir,regular) Reduce evening dose by 20%Reduce morning dose by one third to one half
Short-acting (lispro,aspart, glulisine ) Use with evening meal prior to fastUse to correct glucose >250 mg/mL on fastingday
Sundown to sundown Long- or intermediate-acting (glargine, detemir,regular) Reduce evening dose by one third to one halfReduce morning dose by one third to one half
Short-acting (lispro,aspart, glulisine) Use with evening meal prior to fastUse to correct glucose >250 mg/mL on fasting day
Prolonged fastingsunrise to sundown (eg,Ramadan) Long- or intermediate-acting (glargine, detemir,NPH) Reduce dose by 15%-30%; take at predawn meal
Twice-daily long- orintermediate-acting(glargine, detemir, NPH) Reduce one of the doses (morning or evening) by 50%depending on blood glucose readings
Short-acting (lispro,aspart, glulisine) Reduce evening dose by 50%; normal dose at predawn mealUse to correct glucose >250 mg/mL on fasting day

For patients who use insulin pumps, basal rates should be reduced to prevent hypoglycemia; other aspects of the insulin regimen, such as correction boluses, should remain the same. During a prolonged fast, such as Ramadan, a typical adjustment includes reduction of the basal rate by 20%-40% in the last 3-4 hours of fasting and then increasing the basal rate by 0%-30% after the sunset meal.[8]

In conclusion, patients with insulin-dependent diabetes can fast safely and control blood glucose. Healthcare professionals should evaluate patients who are planning to fast and ensure that they understand the importance of glucose monitoring throughout the fast and how to prevent hypoglycemia.

Practice Pearls:

  • Most insulin-dependent diabetes patients can fast safely and control blood glucose.
  • Healthcare professionals should evaluate patients who are planning to fast and ensure that they understand the importance of glucose monitoring throughout the fast and how to prevent hypoglycemia.


Grajower MM. 24-hour fasting with diabetes: management of religious observances and of the preoperative patient. Diabetes Metab Res Rev. 2011. Epub ahead of print. doi: 10.1002/dmrr.1169.

Grajower MM. Management of diabetes mellitus on Yom Kippur and other Jewish fast days. Endocr Pract 2008;14:305-311.

International Diabetes Federation and Diabetes and Ramadan International Alliance. Diabetes and Ramadan: Practical Guidelines. April 2016. http://www.daralliance.org/daralliance/wp-content/uploads/IDF-DAR-Practical-Guidelines_15-April-2016_low.pdf Accessed December 11, 2016.

Babineaux SM, Toaima D, Boye KS, et al . Multi-country retrospective observational study of the management and outcomes of patients with Type 2 diabetes during Ramadan in 2010 (CREED). Diabet Med 2015;32:819-28.

Zabeen B, Tayyeb S, Benarjee B, et al . Fasting during Ramadan in adolescents with diabetes. Indian J Endocrinol Metab 2014;18:44-7.18.

Kaplan W and Afandi B. Blood glucose fluctuation during Ramadan fasting in adolescents with type 1 diabetes: Findings of continuous glucose monitoring. Diabetes Care 2015;38:e162-e3

Diabetes and Ramadan: Practical Guidelines

Southwest Gastroenterology Associates. Diabetic Medication Instructions for Colonoscopy Preparation and Procedure. 2015.