This post was initially released on October 25, 2020. It has been updated.
Intermittent fasting has many benefits for diabetics. It reduces blood sugar, lowers weight, triglycerides, and total cholesterol, and decreases medication need.
However, people with Type 2 diabetes or adult-onset diabetes who would like to practice intermittent fasting should avoid complications.
Possible Complications of Intermittent Fasting When taking Diabetes Medications
Dehydration and Electrolyte Problems
Excess water and salts like sodium and magnesium are flushed out in the urine as the body responds better to insulin during intermittent fasting.
This is good because it lowers blood pressure and weight and decreases leg swelling.
However, dehydration can occur if the fluid loss is greater than the fluid intake.
This can manifest as dizziness, insomnia, passing out, falls, headaches, weakness, and lightheadedness. Adequate water and added salt intake will prevent dehydration.
Hypoglycemia
People with diabetes have elevated blood sugars that can cause complications like heart attacks, stroke, gangrene, kidney failure, and blindness down the road.
That is why medications to lower blood sugar are prescribed. However, the medicines do not address insulin resistance, so complications remain.
Intermittent fasting makes the body more sensitive to insulin and lowers blood sugar.
Consequently, hypoglycemia can occur when certain medicines are taken while fasting.
Hypoglycemia means low blood sugar. The symptoms are irritability, confusion, sweating, and decreased level of consciousness.
In extreme, it can present as stroke-like symptoms, and it has to be ruled out when someone presents with stroke-like symptoms in the emergency room. Low blood sugar can even lead to coma and death if not recognized and treated.
There is a condition called Hypoglycemia Unawareness. In this situation, the person has very low blood sugar but does not have any symptoms until their consciousness deteriorates.
That is why constant monitoring of blood sugar is essential. People with diabetes should have a glucometer.
Who Should Not Fast?
- Pregnant Diabetics
- Persons with dementia
- Children
- Anyone with a history of eating disorders
- People who had organ transplants on immunosuppressants.
Diabetes medications: What to stop and what to continue
Metformin
Metformin is effective and inexpensive in treating diabetes. It lowers the liver’s blood sugar production, which contributes to high blood sugar in diabetes. It also decreases the intestinal absorption of sugars, increases the body’s glucose use, and increases insulin sensitivity.
Metformin has a low risk of hypoglycemia and can be continued with intermittent fasting. Glucophage, Glucophage XR, Glumetza, Fortamet are brand names of metformin.
Sulfonylureas
Sulfonylureas like glyburide, glipizide, and glimepiride stimulate the pancreas to produce more insulin. The higher insulin levels lower the blood sugar. But sulfonylureas have a side effect. Studies have shown that people who take sulfonylureas tend to have worse outcomes if they develop a heart attack.
Read: Intermittent Fasting vs. Sulfonylureas: Heart Attack Outcomes
Long-acting sulfonylureas like glyburide (DiaBeta™, Micronase™, Glynase™, Glynase PresTab™), glipizide (Glucotrol™, GlipiZIDE XL™, Glucotrol XL™), and glimepiride (Amaryl™) can cause hypoglycemia during intermittent fasting. The doses should be reduced or withheld if taken the night before or the day of the fasting.
Meglitinides
Meglitinides are newer, short-acting sulfonylureas. Nateglinide (Starlix™) and repaglinide (Prandin™) should be withheld during meals without carbohydrates.
Insulins
Injected or inhaled insulin lowers blood sugar by storing what we eat into fat and muscles. However, if a person is inactive, the calories are primarily stored in fat.
All types of injected insulin, whether short or long-acting, can lead to weight gain and worsen obesity. Moreover, injected insulin in Type 2 diabetes worsens the preexisting hyperinsulinemia, which is why insulin is the last recourse in patients with Type 2 diabetes.
There is a high risk of hypoglycemia using long-acting insulins like NPH (Humulin™, Novolin™), Levemir (Detemir™), and Glargine (Basaglar™).
Insulin taken after meals like insulin lispro (Humalog™, Admelog™, Humalog KwikPen™, Lyumjev™), aspart insulin (Novolog™, Fiasp™, NovoLog FlexPen™, NovoLog PenFill™), and insulin glulisine (Apidra™, Apidra SoloStar™) also have a high risk for hypoglycemia, and blood sugar readings should be checked closely and proactively.
Prior studies of intermittent fasting on patients taking insulin decreased the doses by 50% and sometimes 75%.
However, there were still some who had hypoglycemia, which is why constant monitoring and supervision are essential.
SGLT2 Inhibitors
SGLT2s like dapagliflozin (Farxiga™) empagliflozin (Jardiance™), and canagliflozin (Invokana™) lowers the blood sugar by making the kidneys eliminate more sugar in the urine.
SGLT-2 inhibitors do not usually cause hypoglycemia. However, since they eliminate sugar and water through the urine, there may be a danger of dehydration and kidney injury, especially if intermittent fasting is also practiced.
It is better to skip this medicine or drink more water during fasting days.
Additionally, people taking water pills that increase urine output, like furosemide (Lasix™) and hydrochlorothiazide for high blood pressure or heart failure, may need to reduce their dosage if on intermittent fasting to prevent dehydration and kidney injury.
DPP4 Inhibitors
DPP4s or Dipeptidyl peptidase inhibitors like saxagliptin (Onglyza™) and sitagliptin increase insulin secretion. They also prevent glucagon from increasing blood sugar after a meal. Side effects are sore throat, stuffy nose, upset stomach, and diarrhea. DPP4s can be continued.
TZDs, or thiazolidinediones, like pioglitazone (Actos™) and rosiglitazone (Avandia™), lower blood sugar by depositing it into subcutaneous fat. They have a low risk of hypoglycemia and can be continued.
Glucagon-Like Peptide-1 (GLP-1) Receptor Analogues
GLP-1 drugs lower blood glucose if carbohydrates are included in the meal. Dose adjustment for once-weekly injections may not be adjusted.
A daily injection of liraglutide (Victoza™) can be continued because the risk of hypoglycemia is low. Lixisenatide (Lyxumia™ or Adlyxin™) is used to control postprandial hyperglycemia and thus can be withheld during IF days.
Alpha Glucosidase Inhibitors and Bile Acid Sequestrant
Acarbose (Glucobay™, Precose™, and Prandase™) and Miglitol (Glyset™) delays carbohydrate digestion. The result is lower glucose levels. They can be skipped on meals without carbohydrates, not because of hypoglycemia, but they are unnecessary and save money.
Colesevelam (Welchol™ and Cholestagel™) sequesters bile and lowers blood glucose and cholesterol absorption. They can be skipped during intermittent fasting; however, they should be continued if they are taken to lower cholesterol.
Summary
Drugs can cause hypoglycemia while intermittent fasting:
- Insulin
- Sulfonylureas – glyburide, glipizide, and glimepiride
- Meglitinides – nateglinide (Starlix™), and repaglinide (Prandin™)
Medications with low risk of Hypoglycemia while fasting
- Metformin, when taken alone
- DPP4s – saxagliptin (Onglyza™) and sitagliptin (Januvia™)
- TZDs – pioglitazone (Actos™) and rosiglitazone (Avandia™)
- Liraglutide (Victoza™)
Not needed when intermittent fasting
- SGLT2s like dapagliflozin (Farxiga™) and empagliflozin (Jardiance™), and canagliflozin (Invokana™)
- Lixisenatide – not needed during fasting days
- Acarbose (Glucobay™, Precose™, and Prandase™) and Miglitol (Glyset™)
- Colesevelam (Welchol™ and Cholestagel™). Continue if used to lower cholesterol
What about combination medicines?
Some diabetes medications are combinations of the above, like Metaglip, a combination of glipizide and metformin. In a drug combination, if one drug can cause hypoglycemia, like glipizide in this case, then it should be skipped because it can cause hypoglycemia even though metformin is OK to take alone.
Be aware that other medicines can cause drug-induced low blood sugar, including:
- Beta-blockers (such as atenolol or propranolol overdose)
- Cibenzoline and quinidine (heart arrhythmia drugs)
- Indomethacin (a pain reliever)
- Medicines that fight infections (such as gatifloxacin, levofloxacin, pentamidine, quinine, trimethoprim-sulfamethoxazole)
If you plan on doing physical activity while fasting, be aware that it can also lower blood sugar. Ensure you have a sugary drink if you plan to be physically active outside while fasting.
Steps before Intermittent Fasting
- Talk to your physician about your plans for intermittent fasting. Some physicians may not agree with the method and may dissuade you from doing it.
- Check and record your weight and waist circumference for baseline.
- Know your last glycosylated hemoglobin or HbA1c to know how your blood sugar has been controlled over the past three months.
- Be familiar with your list of medicines and all the doses.
- Check your blood sugar in the morning before breakfast and after every meal.
- Check the blood sugar every 2 hours if on insulin and every 4 hours for someone taking sulfonylureas.
- Personal continuous glucose monitoring systems like Dexcom® have hypoglycemia alerts. In contrast, Abbott Freestyle Libre System® does not have an alert. These systems allow frequent testing without additional expense or discomfort.
Medication adjustments may need to be continued the longer you fast. That is why the blood sugars should be recorded. This will help your physicians adjust your diabetes medicines. As weight loss happens, the risk of hypoglycemia increases; therefore, medication adjustments should be made as required.
Recording your blood pressure and heart rate is also a good idea since losing weight will lower your blood pressure. It is possible to be a diet-controlled hypertensive.
Remember to increase fluid intake since water from food is also reduced. Feelings of fatigue and weakness can be from dehydration, and SGLT2 inhibitors, diuretics, and other anti-hypertensive drugs may need to be withheld.
Always talk to your doctor when starting an intermittent fasting program.
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Reference:
Grajower MM, Horne BD. Clinical Management of Intermittent Fasting in Patients with Diabetes Mellitus. Nutrients. 2019;11(4):873. Published 2019 Apr 18. doi:10.3390/nu11040873
Image credit: By Clinical Cases, Ilmari Karonen – Drawn in Inkscape by Ilmari Karonen based on w:Image: Incretins and DPP 4 inhibitors.jpg from http://casesblog.blogspot.com/2006/11/dpp-4-inhibitors-for-treatment-of.html (uploaded by author), CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=1540751
© 2018 – 2022 Asclepiades Medicine, L.L.C. All Rights Reserved
DrJesseSantiano.com does not provide medical advice, diagnosis, or treatment