Intermittent fasting can be safe and effective for glycemic control in patients with type 2 diabetes or metabolic syndrome, according to research results published in Diabetes Research and Clinical Practice.

“Several reviews and meta-analyses have shown that the effect of intermittent and continuous energy restriction on weight loss, lipid profile, and insulin resistance in participants [with] overweight or obesity was comparable [to moderate calorie restriction]”, according to the researchers. “However, the effect of intermittent fasting on glycemic control in patients with type 2 diabetes (T2D) remains inconclusive.” In the current study, investigators reviewed randomized controlled trials (RCTs) comparing intermittent fasting with continuous energy-restricted diet for safety, glycemic control, and weight loss in patients with overweight or obesity with metabolic syndrome or T2D.

A total of 68 studies were identified; 5 RCTs were eligible for inclusion in a systematic review. One study did not report the difference with the studied groups; therefore 4 studies representing a total of 355 participants were analyzed.   

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Study sample size ranged from 31 to 137, and intervention duration ranged from 8 weeks to 12 months. Two studies enrolled participants with T2D and 2 enrolled patients with metabolic syndrome.

Attrition rates ranged from 0% to 29.2%, with similar rates between intervention and control groups. No studies reported on compliance with dietary interventions, although 1 study reported a total of 7 individuals (2 from the experimental group and 5 from the control group) who dropped out due to an inability to follow the diet.

In one of the studies, all hypoglycemia events occurred in patients who were using sulfonylureas and/or insulin. Participants who experienced hypoglycemia were not sure if it had also occurred prior to the trial. There was no difference between the groups in the number of hypoglycemic events (mean: control group, 2.0[1.0] vs treatment group, 2.5[0.8], P=.74).

The same study reported a total of 10 participants who experienced hyperglycemia across the intermittent fasting and control groups (7 and 3, respectively). Another study reported adverse events, including mild headache, dizziness, mild nausea, and temporary sleep disturbance.

One study did not compare antidiabetic drugs between groups, and another study excluded patients taking insulin with a fasting plasma glucose >16.7 mmol/L after medications were discontinued. A third study implemented a drug reduction plan during the intervention phase based on the patients’ glycated hemoglobin (HbA1c) levels to compare the between-group change in medication effect score.

In the meta-analysis, researchers reviewed glycemic control, change in weight, and lipid profile. Three studies reported changes in HbA1c levels with no statistical difference between the intermittent fasting and control groups (mean difference, -0.06). Three studies reported changes in fasting glucose levels, with no difference between the two groups (mean difference, -0.27). Two studies reported a change in levels of fasting insulin, with no significant difference between the groups (mean difference, -0.17).

All 4 studies reported a change in patient weight before and after the diet intervention. When data were statistically pooled, the change in weight was -1.70 kg (95% CI, -3.28, -0.11 kg), indicative that intermittent fasting was more effective than continuous energy restriction in successful weight loss.

Three trials also reported an improvement in BMI, and the meta-analysis showed no difference between the groups (mean difference, -0.31).

No statistical difference was noted in patient lipid profiles, which included values of total cholesterol, triacylglycerol, LDL cholesterol, and HDL cholesterol.

Heterogeneity among the trials, diet regimens, and the limited number of RCTs whose sample size was not large and met inclusion criteria.

“[Intermittent fasting] is a safe diet pattern and could be implemented for patients with [T2D] or metabolic syndrome,” the researchers concluded. “Further studies with a larger sample size are needed to verify the effectiveness and safety of [intermittent fasting] in patients with [T2D].”


Wang X, Li Q, Lui Y, Jiang H, Chen W. Intermittent fasting versus continuous energy-restricted diet for patients with type 2 diabetes mellitus and metabolic syndrome for glycemic control: a systematic review and meta-analysis of randomized controlled trials. Diabetes Res Clin Pract. Published online August 12, 2021. doi: 10.1016/j.diabres.2021.109003