In new research, scientists at the University of Surrey tested the hypothesis that the human circadian system anticipates large meals.
In a controlled laboratory protocol, Isherwood et al. investigated if the human circadian system anticipates large meals. Image credit: Rita E.
Circadian rhythms/systems are physiological changes, including metabolic, 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.
“We often get hungry around the same time every day, but the extent to which our biology can anticipate mealtimes is unknown,” said University of Surrey’s Professor Jonathan Johnston, senior author of the study.
“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.
The authors 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.
“What we have found is that the human body is rhythmically programmed to anticipate mealtimes particularly when food is not readily accessible,” Professor Johnston said.
“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.”
The results appear in the journal Current Biology.
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Cheryl M. Isherwood et al. Human glucose rhythms and subjective hunger anticipate meal timing. Current Biology, published online February 22, 2023; doi: 10.1016/j.cub.2023.02.005
