Summary: Our bodies can predict the time of regular meals, according to a new study. Additionally, a person’s daily blood sugar rhythms can be determined by meal size in addition to meal time.
Source: University of Surrey
The human body can predict the time of regular meals, according to a new study from the University of Surrey. The research team also discovered that daily blood sugar rhythms can be determined not only by meal times, but also by meal size.
In the first study of its kind, Surrey researchers, led by Professor Jonathan Johnston, investigated whether 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 with environmental cues, such as light and dark cycles.
Previous studies in this area have focused on control animals and so far it has not been determined whether human physiology can predict mealtimes and food availability.
Jonathan Johnston, professor of chronobiology and integrative physiology at the University of Surrey, said: “We are often hungry around the same time each day, but the extent to which our biology can anticipate meals is unknown. It’s possible that metabolic rhythms align with meal patterns, and meal regularity means that we eat when our bodies are best suited to deal with it.
To find out more, 24 male participants undertook an eight-day lab study with strict sleep-wake schedules, exposure to light-dark cycles, and food intake. For six days, 12 participants consumed small meals every hour throughout the waking period, with the remaining participants consuming two large meals daily (7.5 and 14.5 hours after waking).
After six days, all participants were then put on the same eating schedule for 37 hours and given small meals every hour 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, then every hours for the last 37 hours.
By analyzing the results of the first six days of the study, the researchers found that the glucose concentration of the participants in the small meal group increased upon awakening and remained high throughout the day until decreasing after their last meal. In the large meal group, there was a similar increase in glucose concentration upon awakening, but there was a gradual decline before the first meal.
Over the past 37 hours, when both groups received the same small meals every hour, all participants showed an initial rise in glucose concentration upon waking. However, in those who had already received two large meals, blood sugar levels began to drop before the scheduled large meal (which they did not receive) while for participants who had always consumed small meals every hour, their blood sugar continued to rise as seen previously.
Additionally, in the large meal group, there was an increase in hunger before projected meal times that decreased sharply after the projected meal time.
Professor Johnston added: ‘What we have discovered is that the human body is rhythmically programmed to anticipate meal times, particularly when food is not readily available. This suggests that there is a physiological drive for some people to eat at certain times because their bodies have been trained to expect food rather than 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
Picture: Image is in public domain
Original research: Free access.
“Human Glucose Rhythms and Subjective Hunger Anticipate Mealtime” by Jonathan D. Johnston et al. Current biology
Human glycemic rhythms and subjective hunger anticipate mealtimes
- Glucose concentration drops in anticipation of a predictable large afternoon meal
- In constant routine, glycemic rhythms have a nadir during previous important meals
- In a constant routine, hunger scores anticipate previous important meals
- Melatonin rhythms are not altered by meal pattern
Circadian rhythms, metabolism and nutrition are closely linked.
The timing of a three-meal daily eating pattern synchronizes certain human circadian rhythms.
Despite animal data showing anticipation of food availability, linked to a food-trainable oscillator, it is unclear 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 small hourly meals throughout the waking period or two large meals daily (7.5 and 14.5 h after waking).
All participants then embarked on a consistent 37-hour routine. Interstitial glucose was measured every 15 minutes throughout the protocol. Hunger was assessed hourly during waking periods. Salivary melatonin was measured in the constant routine.
During the 6-day feeding regimen, both groups showed an increase in glucose concentration early each morning. In the small meal group, glucose concentrations continued to rise throughout the day. However, in the large meal group, glucose concentrations decreased from 2 h after waking until the first meal.
Mean 24-h glucose concentration did not differ between groups. In the constant routine, there was no difference in the occurrence of melatonin between the groups, but antiphasic glycemic rhythms were observed, with low blood sugar at previous meals in the large meal group.
Additionally, in the large meal group, consistent routine hunger scores increased before scheduled meal times. These data confirm the existence of human food anticipation.