Do you ever wonder why you typically feel hungry when it's time for dinner?
Researchers say that's not just a habit, but a physiological drive, with the human body able to predict the timing of regular meals.
“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,” said study author Jonathan Johnston. He is a professor of chronobiology and integrative physiology at the University of Surrey in the United Kingdom.
To investigate if the human circadian system anticipates meals, the researchers worked with 24 men in an eight-day laboratory study with strict sleep-wake schedules.
For six days, 12 participants consumed small meals hourly throughout the waking period. The other 12 participants ate two large daily meals at 7.5 and 14.5 hours after waking.
After those six days, all the participants were given the same eating schedule for 37 hours. They received small meals hourly in a procedure known to reveal internal circadian rhythms. Researchers measured the participants' glucose (blood sugar) every 15 minutes during the study.
The participants shared their hunger levels 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 investigators found the glucose concentration of participants in the small-meal group increased upon waking. Those results remained elevated throughout the day before declining after their last meal.
In the large-meal group, the researchers saw a similar increase in glucose concentration upon waking. Those participants had a gradual decline leading up to the first meal.
During the final 37 hours, as the two groups ate the same meals at the same time, all participants had an initial rise in glucose concentration when they woke.
However, in those who had previously received two large meals, glucose levels began to decline before the anticipated large meal — a meal which they did not receive.
In participants who had always consumed small meals hourly, their glucose levels continued to rise as previously seen.
The large-meal group also had an increase in hunger before their projected mealtimes. That hunger 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,” Johnston said in a university news release. “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 findings were published online recently in the journal Current Biology.
The U.S. National Institutes of Health has more on circadian rhythms.
SOURCE: University of Surrey, news release, Feb. 22, 2023