Intermittent Fasting May Not Be the Diet for Patients with Type 2 Diabetes

Intermittent fasting may help reduce body fat, but how safe is it in a patient with type 2 diabetes?

Intermittent fasting has become very popular. It includes various nutritional behaviors that allow a break of food consumption for extended periods that could range from hours to a full day on a regular intermittent schedule. Compared to caloric restriction, intermittent fasting had similar positive effects on blood pressure, cognitive function, cholesterol levels, inflammation, and weight. Maintaining an intermittent fast can be challenging and hard to sustain, as shown in a study with “attrition rates of 27% to 40%” in their intermittent fasting groups. For intermittent fasting to help in the prevention of chronic diseases like type 2 diabetes, it would need to be sustained over decades, which may not be feasible.

Calorie restriction has been known to help with insulin resistance. Intermittent fasting has shown similar results to calorie restriction in reducing insulin levels and increasing insulin sensitivity. During intermittent fasting, the body utilizes energy from fatty acids and ketones, increasing the amount of insulin resistance; however, insulin sensitivity returns during eating. While there seem to be favorable outcomes for intermittent fasting, there is still a concern for its safety in patients with type 2 diabetes. Intermittent fasting is known to cause dehydration and hypotension, amongst other safety concerns. Although insulin and insulin secretagogues are famous for causing hypoglycemia, all antidiabetic medication poses a concern for hypoglycemia.

Efficacy of intermittent fasting on A1C levels is non-inferior to the caloric restriction, as shown in a study where intermittent fasting decreased by 3%, and caloric restriction had a decrease of 0.5%. While the efficacy of intermittent fasting may be similar to caloric restriction, its safety may be less. Authors of the viewpoint article were interested in the safety of intermittent fasting for patients with type 2 diabetes. They observed the seven studies published on intermittent fasting for patients with type 2 diabetes, including five randomized controlled trials that compared intermittent fasting to caloric restriction. Most of the studies had different fasting frequencies, including fasting for 18-20 hours a day for two weeks, fasting two days a week for 12 weeks, fasting two days per week for 12 months, fasting 3 to 4 days a week for 7 to 11 months, fasting four days a week for 12 weeks, and fasting one day out of the week for four months.

All studies proved beneficial in quality of life and glucose improvement with no insulin resistance. However, the risk for macrovascular and microvascular complications may be a concern due to significant variations of glucose during intermittent fasting. A person may present with hypoglycemic episodes during intermittent fasting and hyperglycemic episodes during food consumption.

Medication for diabetes needs to be adjusted appropriately and carefully in patients considering an intermittent fasting regimen. Authors of the new viewpoint study suggest continuous glucose monitoring for clinical intervention in patients with type 2 diabetes who are doing intermittent fasting. Type 2 diabetes patients should not attempt intermittent fasting without talking to a physician. Although there are no comparative trials for medication regimens in this population, medication adjustment proposals are still based on known adverse effects and mechanisms of action of diabetes medications. The goal in the future would be to determine an appropriate diabetes medication regimen for individuals considering intermittent fasting. At this time, intermittent fasting is non-inferior to calorie restriction in terms of efficacy, while the full adverse effects of intermediate fasting on type 2 diabetes patients are unknown.

Practice Pearls:

• Intermittent fasting causes fluctuations in glucose level and may lead to coronary disease and retinopathy.
• Calorie restriction and intermittent fasting are non-inferior in their positive effects on A1C and weight loss.
• Hypoglycemic episodes are a primary concern with antidiabetic medication. Suggestions on how to adjust medication while doing an intermittent fast should be communicated by a physician, because of the risk of hypoglycemic episodes with intermittent fasting. Keep in mind that knowledge is still limited in this area.

Horne, Benjamin D. et al. “Limited Evidence For The Health Effects And Safety Of Intermittent Fasting Among Patients With Type 2 Diabetes”. JAMA, 2020. American Medical Association (AMA), doi:10.1001/jama.2020.3908. Accessed 11 July 2020.

Zahra Hashemy, PharmD. Candidate, USF Taneja College of Pharmacy

See more of our coverage of intermittent fasting.