Well-timed meals decrease risk of glucose intolerance despite improper sleep: Study

According to a study by Brigham and Women's Hospital, night-time eating can lead to glucose intolerance, while daytime meals can help regulate bloodstream glucose levels.

The research has been published in the 'Science Advances Journal'.

Night-time eating appeared to cause a misalignment between the body's central and peripheral circadian "clocks" -- natural timekeepers that regulate physical, mental, and behavioral changes over a 24-hour cycle.

"These results indicate that meal timing was primarily responsible for the reported effects on glucose tolerance and beta-cell function, possibly due to the misalignment of central and peripheral 'clocks' throughout the body," said co-corresponding author Frank A.J.L. Scheer, PhD, MSc, of the Department of Medicine and the director of the Medical Chronobiology Program in the Division of Sleep and Circadian Disorders at the Brigham.

"While the central circadian 'clock' was still on Boston time, the endogenous circadian glucose rhythms suggest that some peripheral 'clocks,' as perhaps those in the liver, had dramatically shifted to a time zone in Asia," Scheer added.

Glucose intolerance led to high glucose levels and often preceded type 2 diabetes mellitus (T2DM), a condition in which the body is less able to absorb sugar from the bloodstream into its tissues. T2DM is prevalent among night shift workers who typically sleep during the daytime and eat during the nighttime. Previous laboratory studies showed increased levels of blood glucose in both non-shift workers and shift workers who underwent simulated night work, said co-corresponding author Sarah L. Chellappa, MD, PhD, formerly of the Medical Chronobiology Program and now of the Department of Nuclear Medicine at the University of Cologne in Germany. They added that shift workers, while frequently exposed to mistimed meals, are not necessarily "immune" to their adverse effects.

This study, a randomized controlled trial, involved 19 healthy young participants who underwent a 14-day controlled laboratory protocol. During the study, participants stayed awake for 32 hours in a highly controlled, dimly lit environment, where they kept constant body posture, consumed identical snacks every hour, and had no time cues -- conditions that are part of a constant routine protocol. After that, the participants underwent simulated night work and followed one of two eating schedules: one group ate during the night-time to simulate a schedule typical among night-shift workers, while the other group ate during the daytime, thus aligning their meal schedule to the 24-hour cycle of the central circadian "clock." Subsequently, participants followed a second, 40-hour constant routine protocol to assess the after-effects of the meal schedules on their endogenous circadian rhythms.

According to the research, participants who ate during the night-time showed increased blood glucose levels, while those who ate only during the daytime showed no significant changes. In addition, night-time eating decreased pancreatic beta-cell function compared to no observable changes in those eating only during the daytime. Beta cells produce insulin, a hormone that escorts glucose into body tissues. Furthermore, night-time eating caused a misalignment between the central circadian "clock," estimated from the endogenous circadian rhythm in core body temperature, and the endogenous circadian glucose rhythms. In stark contrast, these rhythms remained aligned when participants ate meals only during the daytime despite their mistimed sleep.

"Of the participants studied, those with the biggest disruption of their circadian system -- here quantified as the misalignment between their central circadian 'clock' and their endogenous circadian glucose rhythms -- showed the largest impairment of glucose tolerance," said Scheer.

The study's take-home message indicated that daytime eating, despite mistimed sleep, maintained internal circadian alignment and prevented glucose intolerance. The authors noted that more research needs to be conducted to find practical interventions to implement daytime eating in real-life shift workers.