Human Body Can Predict Mealtimes

Summary: Our bodies can predict the timing of regular meals, a new study reports. Additionally, a person’s daily blood-glucose rhythms may be driven by meal size in addition to meal time.

Source: University of Surrey

The human body can predict the timing of regular meals, according to a new study from the University of Surrey. The research team also found that daily blood glucose rhythms may be driven not only by meal timing but by meal size.

In the first study of its kind, researchers from Surrey, led by Professor Jonathan Johnston, investigated if the human circadian system anticipates large meals. Circadian rhythms/systems are physiological changes, including metabolic ones, that follow a 24-hour cycle and are usually synchronized to environmental signals, such as light and dark cycles.

Previous studies in this field have focused on animal controls and until now it has been undetermined whether human physiology can predict mealtimes and food availability.

Jonathan Johnston, Professor of Chronobiology, and Integrative Physiology at the University of Surrey said, “We often get hungry around the same time every day, but the extent to which our biology can anticipate mealtimes is unknown. It is possible that metabolic rhythms align to meal patterns and that regularity of meals will ensure that we eat at the time when our bodies are best adapted to deal with them.”

To learn more, 24 male participants undertook an eight-day laboratory study with strict sleep-wake schedules, exposure to light-dark cycles, and food intake. For six days, 12 participants consumed small meals hourly throughout the waking period, with the remaining participants consuming two large daily meals (7.5 and 14.5 hours after waking).

After six days, all participants were then put on the same feeding schedule for 37 hours and received small meals hourly in a procedure known to reveal internal circadian rhythms. Glucose was measured every 15 minutes during the study, and hunger levels were measured hourly during waking hours on days two four and six in the first stage of the study and then hourly for the final 37 hours.

This shows a table set up for a meal
Circadian rhythms/systems are physiological changes, including metabolic ones, that follow a 24-hour cycle and are usually synchronized to environmental signals, such as light and dark cycles. Image is in the public domain

Analyzing results of the first six days of the study, researchers found the glucose concentration of participants in the small meal group increased upon waking and remained elevated throughout the day until declining after their last meal. In the large meal group, there was a similar increase in glucose concentration upon waking however there was a gradual decline leading up to the first meal.

In the final 37 hours, when both groups were fed the same small meals hourly, all participants exhibited an initial rise in glucose concentration upon waking. However, in those who had previously received two large meals, glucose levels began to decline before the anticipated large meal (which they did not receive) whereas for participants who had always consumed small meals hourly, their glucose levels continued to rise as previously seen.

In addition, in the large meal group, there was an increase in hunger preceding projected mealtimes which sharply declined after the anticipated mealtime had passed.

Professor Johnston added, “What we have found is that the human body is rhythmically programmed to anticipate mealtimes particularly when food is not readily accessible. This suggests that there is a physiological drive for some people to eat at certain times as their body has been trained to expect food rather than it just being a psychological habit.”

About this circadian rhythm and metabolism research news

Author: Press Office
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


Human glucose rhythms and subjective hunger anticipate meal timing


  • Glucose concentration reduces in anticipation of a predictable large afternoon meal
  • In constant routine, glucose rhythms have a nadir at previous large meal times
  • In constant routine, hunger scores anticipate previous large meal times
  • Melatonin rhythms are not altered by meal pattern


Circadian rhythms, metabolism, and nutrition are closely linked.

Timing of a three-meal daily feeding pattern synchronizes some human circadian rhythms.

Despite animal data showing anticipation of food availability, linked to a food-entrainable oscillator, it is unknown whether human physiology predicts mealtimes and restricted food availability.

In a controlled laboratory protocol, we tested the hypothesis that the human circadian system anticipates large meals.

Twenty-four male participants undertook an 8-day laboratory study, with strict sleep-wake schedules, light-dark schedules, and food intake. For 6 days, participants consumed either hourly small meals throughout the waking period or two large daily meals (7.5 and 14.5 h after wake-up).

All participants then undertook a 37-h constant routine. Interstitial glucose was measured every 15 min throughout the protocol. Hunger was assessed hourly during waking periods. Saliva melatonin was measured in the constant routine.

During the 6-day feeding pattern, both groups exhibited increasing glucose concentration early each morning. In the small meal group, glucose concentrations continued to increase across the day. However, in the large meal group, glucose concentrations decreased from 2 h after waking until the first meal.

Average 24-h glucose concentration did not differ between groups. In the constant routine, there was no difference in melatonin onset between groups, but antiphasic glucose rhythms were observed, with low glucose at the time of previous meals in the large meal group.

Moreover, in the large meal group, constant routine hunger scores increased before the predicted meal times. These data support the existence of human food anticipation.

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