Fasting Recommendations for Patients With Insulin-Dependent Diabetes

Andrea G. Scott, PharmD, MPH

Disclosures

February 15, 2017

Question

Can patients with insulin-dependent diabetes safely fast for medical or religious reasons?

Response from Andrea G. Scott, PharmD, MPH
Pharmacist, StoneSprings Hospital Center, Dulles, Virginia

Fasting is a challenge for all patients but can be particularly difficult for patients with insulin-dependent diabetes. Patients may have to fast for laboratory tests, surgery, diagnostic procedures (eg, colonoscopy), or religious reasons.

The duration of the fast is also important because it can affect how much insulin a patient will need during that time.

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).

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.[4,5]

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 adjustment 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[3,6,7]

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 fast
Use to correct glucose
>250 mg/mL on fasting
day
Sundown to sundown Long- or intermediate-
acting (glargine, detemir,
regular)
Reduce evening dose by
one third to one half
Reduce morning dose by
one third to one half
Short-acting (lispro,
aspart, glulisine)
Use with evening meal
prior to fast
Use to correct glucose
>250 mg/mL on fasting
day
Prolonged fasting
sunrise to sundown (eg,
Ramadan)
Long- or intermediate-
acting (glargine, detemir,
NPH)
Reduce dose by 15%-
30%; take at predawn
meal
Twice-daily long- or
intermediate-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 meal
Use 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.[7]

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.

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