Summary: New research shows the human body can anticipate the timing of regular meals. The study also indicates that daily blood-glucose rhythms are influenced by both when and how much we eat.
Source: University of Surrey
Researchers at the University of Surrey report that the human body appears to predict regular mealtimes, and that meal size as well as meal timing can shape daily blood-glucose patterns.
In a first-of-its-kind human study, a team led by Professor Jonathan D. Johnston examined whether the circadian system can anticipate large meals. Circadian rhythms are daily physiological cycles, including metabolic processes, that are typically synchronized with environmental cues such as light and dark.
Previous work demonstrating food anticipation has largely come from animal studies, leaving uncertainty about whether human physiology can similarly predict when food will be available. This new controlled human study addresses that gap by testing whether predictable meal patterns alter glucose rhythms and subjective hunger.
Professor Johnston, Chair of Chronobiology and Integrative Physiology, explained, “People often feel hungry around the same times each day, but it was unclear how much of that is driven by biological rhythms rather than habit. Our results suggest metabolic systems can be trained to expect food at particular times, and that meal size helps shape those anticipatory signals.”
Twenty-four healthy male volunteers completed an eight-day laboratory protocol with tightly controlled sleep–wake cycles, light exposure, and meal schedules. For six days, half the participants received frequent small meals every hour during waking hours, while the other half ate two large meals each day, timed at 7.5 and 14.5 hours after waking.
Following this six-day feeding phase, all participants entered a 37-hour constant routine in which they received identical small meals hourly. This constant routine is a standard method used to reveal internal circadian signals independent of external behaviors. Interstitial glucose was measured every 15 minutes throughout the study. Participants also rated their hunger hourly during waking hours on days two, four, and six, and then hourly during the final 37 hours.
During the initial six-day feeding schedules, participants in the small-meal group showed a rise in glucose after waking that persisted through the day until it fell after their last meal. In contrast, the large-meal group also experienced a morning glucose rise but then showed a gradual decline in glucose levels in the hours leading up to their first large meal.
When all participants switched to the identical hourly small meals during the 37-hour constant routine, everyone showed an early morning rise in glucose on waking. However, participants previously on the two-meal pattern displayed a decline in glucose before the time they had been trained to expect a large meal, despite not receiving that large meal during the routine. Participants accustomed to hourly small meals continued to show the daytime glucose rise characteristic of their prior pattern.
Subjective hunger measures mirrored these metabolic trends: people who had been eating two large meals reported a pronounced increase in hunger before their expected meal times and a sharp drop after those times passed, even when the meal did not occur.
Professor Johnston noted that these results point to a physiological drive that prepares the body for predictable food intake. Rather than a purely psychological habit, the body appears rhythmically programmed to anticipate food availability, particularly when meals have been regular and restricted in timing.
About this circadian rhythm and metabolism research news
Author: Press Office, University of Surrey
Source: University of Surrey
Contact: Press Office – University of Surrey
Image: The image is in the public domain
Original Research: Open access. “Human glucose rhythms and subjective hunger anticipate meal timing” by Jonathan D. Johnston et al. Current Biology.
Abstract
Human glucose rhythms and subjective hunger anticipate meal timing
Highlights
- Glucose levels decrease in anticipation of a predictable large afternoon meal.
- Under constant conditions, glucose reaches a low point at times corresponding to previous large meals.
- Hunger ratings in the constant routine anticipate prior large-meal times.
- Melatonin rhythms remain unchanged by meal pattern.
Summary
This controlled laboratory study demonstrates that human circadian and metabolic systems are influenced by habitual feeding schedules. Timing and size of meals shape daily glucose rhythms and subjective hunger patterns.
Over six days, distinct feeding patterns—either frequent small meals or two larger meals—produced different glucose trajectories across the day, despite no overall change in average 24-hour glucose between groups. When tested under a constant routine that removes behavioral and environmental cues, participants previously on a two-meal schedule showed glucose and hunger changes timed to their habitual meal times, indicating an internal anticipatory mechanism.
These findings support the concept of human food anticipation: metabolic and subjective signals can align with predictable patterns of food availability. The data highlight how meal regularity and size interact with circadian biology, with implications for understanding appetite regulation, glucose control, and the timing of eating in daily life.