Confining Eating to Daytime May Help Night Shift Workers Avoid Glucose Intolerance

Asian senior or elderly old lady woman patient eating breakfast vegetable healthy food with hope and happy while sitting and hungry on bed in hospital.
With night work being known to increases the risk of diabetes, researchers simulated working at night and examined whether people exhibit internal circadian misalignment and impaired glucose tolerance and what happens when they eat during the night compared with eating during the day.

Eating meals only during the day may help night shift workers mitigate the adverse effects of their schedule on glucose tolerance and pancreatic β cell function, according to new research from Science Advances.

Researchers included 19 healthy individuals (12 men 7 women aged 26.5±4.1 years body mass index (BMI) 22.7±2.1 kg/m2) in a 14-day circadian laboratory protocol under 32-hour sustained wakefulness, semirecumbant posture, dim light intensity, and hourly isocaloric snacks and forced desynchrony (FD) protocol in dim light for 4 28-hour “days.”

A nighttime meal control (NMC) group of 10 participants underwent the 28-hour protocol with meals at fixed times relative to scheduled wake times, eating during the daytime and nighttime, leading to a 12-hour postalignment constant routine (CR). In the daytime meal intervention (DMI), 9 individuals consumed meals only during the daytime, resulting in a 40-hour postalignment CR.

Restricting meals to only occurring in the daytime altered the impact of simulated night work on the 3-hour postprandial glucose profile after the breakfast test meal (mixed-model analyses of variance: interaction of meal timing group and simulated day/night work pFDR =.003). The postprandial glucose profile increased 19.4% (95% CI 4.7% to 34.2% P =.002) from baseline. The DMI group did not experience significant changes (95% CI -13.9% to 10.1%).

The NMC group experienced a 52.9% reduction in (95% CI -98.6% to -7.1%) postprandial early-phase insulin after the breakfast test meal. The DMI group did not experience a significant difference (95% CI -39.8% to 3.4%).

The researchers found that the NMC group, but not the DMI group, experienced significant changes in the endogenous circadian glucose rhythms compared with baseline (P =.003). The 2 groups had significantly different change in the endogenous circadian glucose rhythms from baseline to simulated night work (mean direction ± circular variance: NMC group, 9.81±0.11 hours; DMI group, 0.57±0.11 hours; Watson-Williams F test, P <.001).

Simulated night work increased the average glucose profile among the NMC group 6.4% from baseline (95% CI 2.7% to 10% (6.3 mg/dl; 95% CI, 3.3 to 9.7 mg/dl) Tukey’s post hoc test adjusted for multiple comparisons P =.003). The DMI group did not experience a significant effect compared with baseline (95% CI, −1.7 to 4.2% (−0.2 to 4.1 mg/dl); Tukey’s post hoc test adjusted for multiple comparisons P = n.s.).

The amount of internal circadian misalignment was linked with decreased glucose tolerance during the simulated night work (r = 0.86 P <.001).

Limitations involved generalization to individuals with sleep disorders or without good health and small differences in fasting duration.

“As permanent or rotating night shifts are unlikely to result in adequate circadian adjustment in most individuals, the alignment of fasting/eating cycle to the central circadian pacemaker may prevent glucose intolerance in most shift workers,” the researchers said.

Disclosure: Some study authors declared affiliations with biotech, pharmaceutical, and/or device companies. Please see the original reference for a full list of authors’ disclosures.


Chellappa SL, Qian J, Vujovic N, et al. Daytime eating prevents internal circadianmisalignment and glucose intolerance in night work. Sci. Adv. Published online December 3, 2021. doi:10.1126/sciadv.abg9910