Scientific research has proven that we burn different amount of calories when we rest depending on the time of day. Early in the morning, individuals burn approximately 10% fewer calories compared with the late afternoon and evening.
The new data helped to confirm the significance of circadian clock in presiding over metabolism. Thanks to these findings, we can now provide a better explanation why irregular eating habits and sleeping at a different time caused by a shift work may lead to obesity.
The most surprising discovery is that keeping a daily routine helps to burn much more calories than activities done at a random time.
The experiment was conducted with seven people who were placed in a laboratory that didn’t have windows or clocks so that the subjects couldn’t keep track of the time of the day. They were not allowed to use gadgets or the Internet either. Such conditions were necessary to determine metabolic fluctuations during the day regardless of physical activity, sleep cycle, and diet. The subjects lived according to a pre-planned sleep and waking schedule. Every night for 3 weeks, the sleeping time was shifted four hours later. This corresponds to traveling west through 4 time zones. Thus, within the frames of the experiment, each of the subjects made a round-the-world trip every week.
Since the subjects’ internal clocks did not have a chance to react to temporal changes, the internal processes in their bodies began to occur at their own pace. Thus, the researchers were able to measure the metabolic rate at all biological times of the day.
The data obtained demonstrated that the calorie burn during the rest is the lowest in the circadian phase that the research team marked as ~ 0 °. A slowdown in metabolism corresponds to a reduction in the temperature of the body that occurs on a late biological night. At the circadian phase labelled ~ 180°, on the contrary, energy expenditure was the highest. This phase corresponds to the biological day and early evening.
The subjects’ respiratory coefficient, which determines the absorption of macronutrients, also fluctuated depending on the circadian phase. The indicators decreased in the evening and went up in the biological morning.
The results of the experiment allowed making a characteristic of the circadian profile in resting energy expenditure as well as fasted respiratory coefficient apart from the effects of activity, sleep-wakefulness cycle, and diet.
It is important to understand that the amount of calories we burn is not only affected by what we eat but also when we eat and rest. Regular sleep and eating habits are critical for overall health and well-being.