Currently experiencing a surge in popularity, intermittent fasting has become an increasingly adopted dietary regimen due to its many purported health benefits. The concept of intermittent fasting refers to a spectrum of nutritional behaviors that aim to intentionally disrupt energy consumption for extended periods of time, for example, for between 16 and 24 hours on a regular intermittent schedule. In some intermittent regimens, individuals restrict food consumption to a 6- to 8-hour period, while in others they fast for a full 24 hours during several days of the week.

Some individuals may be inclined to adopt these dietary patterns as a means of weight loss or for their promised health benefits supported by anecdotal evidence, including the treatment of type 2 diabetes which remains unproven and untested entirely. While caloric restriction and weight loss are known to beneficially influence health outcomes in patients with type 2 diabetes – leading to improved glucose control, hypertension, and abnormal lipid levels – achieving them with intermittent fasting presents concerns.

Published on July 2, 2020 in JAMA, a new viewpoint underscores the limited body of evidence of the health benefits of intermittent fasting among type 2 diabetes patients and reveals the potential adverse complications that may result from this approach if patients are not carefully monitored.

Intermittent Fasting and T2D

To date, intermittent fasting in patients with T2D has only been studied in a few small, short-term trials yielding limited evidence of its benefit. Recently, a team of researchers examined the evidence for the health benefits and safety of intermittent fasting in this group of patients specifically. For the purposes of the study, intermittent fasting was defined as time-restricted feeding, or fasting on alternate days or during 1-4 days of the week, with only water, juice, or bone broth and no more than 700 calories consumed on fasting days.

In total, the study’s authors found seven published studies of fasting in T2D patients – only one trial had over 63 patients. Most studies were short in duration, occurring over 4 months or less, and evaluated five different fasting frequencies. All reported a connection between intermittent fasting and weight loss, while the majority also noted decreased A1c and improved glucose levels, quality of life, and blood pressure. Due to the lack of homogeneity in design, measures, and regimen styles, clinically meaningful conclusions could not be drawn.

In addition, only one study addressed the safety of two intermittent fasting regimens, finding that both increased the incidence of hypoglycemic events despite the use of a medication dose-change protocol.

Improved Glucose, Heightened Risks

The primary implication of the latest findings is that intermittent fasting may be less safe than caloric restriction, although it could be equivalently effective. Patients with existing diabetes who experienced weight loss saw a benefit of improved glucose, blood pressure, and lipid levels, according to the researchers.

While weight loss associated with intermittent fasting appears to be similar to that attained with caloric restriction, in the case of type 2 diabetes patients it can pose a risk of glycemic variability. Hypoglycemia can occur during fasting and hyperglycemia during feeding times, researchers note, and presents potentially dangerous clinical implications.

“Studies have raised concern that glycemic variability leads to both microvascular (eg, retinopathy) and macrovascular (eg, coronary disease) complications in patients with type 2 diabetes,” the authors cautioned. As such, the report highlights the need for continuous glucose monitoring aimed at detecting glycemic variability in susceptible patients as well as throughout studies of clinical interventions involving intermittent fasting in T2D patients.

Recommendations

Although further evidence is needed, the study’s lead author, Benjamin D. Horne, PhD, MStat, MPH, concluded that he would recommend intermittent fasting for patients with type 2 diabetes with caveats due to safety issues. These can include factors such as low blood pressure, weakness, headaches, dizziness – all of which are important considerations alongside the risk for hypoglycemia. Thus, caloric restriction may be a safer choice for certain patients.

Horne recommends giving patients intervention options to choose from as some may be better positioned to handle intermittent fasting. Until intermittent fasting is proven more effective at controlling diabetes, the currently available study data implicate that such regimens for patients with type 2 diabetes should be approached with caution, the risk of hypoglycemia closely monitored, and medications carefully adjusted to ensure both safety and efficacy of nutritional interventions.