Marked Increases in Continuous Glucose Monitor-Detected Hypoglycemia During a Seven-Day Water-Only Fast in Healthy Men and Women

Background: Multiday fasting is practiced globally for various health or religious reasons which can cause marked declines in circulating glucose levels. Yet, the extent of hypoglycemia exposure (ie, blood glucose <70 mg/dL), as measured by continuous glucose monitoring (CGM) during a prolonged fast is unclear. We aimed to determine the distribution of interstitial glucose data as measured by CGM, during a seven-day water-only fast in healthy men and women. Methods: This study used interstitial glucose levels from CGM (Dexcom G4 Platinum) to profile hypoglycemic exposure during a seven-day water-only fast in 12 healthy adults (seven men; age 29.7 ± 6.1 years; body mass index [BMI] 25.0 ± 3.3 kg/m²) that also included physical performance tests (day 6) and an oral glucose tolerance test (day 7). Results: Time <70 mg/dL increased from 3.0% ± 7.1% at baseline to 66.0% ± 25.7% by day 5 ( P < .001). Minimum daily glucose levels also declined from 76 ± 14 mg/dL at baseline to 50 ± 7 mg/dL by day 5 ( P < .001). The performance tests and the oral glucose tolerance test markedly increased glycemia. No symptoms of hypoglycemia were reported. Conclusions: This research demonstrated considerable hypoglycemia exposure occurs without symptoms in heathy men and women who undertake multiday fasting.