Ever wondered why we get jet lag? The dramatic change in the light and dark cycle leaves the traveller with fatigue and exhaustion. Often the explanation is that the 'body clock' is taking time to adapt to the new time zone. Surprisingly, this explanation makes perfect sense scientifically, except for a few differences.
We have a 'central clock' in our brain that schedules its ticks in response to the lights received on the eye's retina. Moreover, they also found many such clocks (peripheral clocks) in all other organs that are controlled by the central clock. In short, the central clock is a master that mediates the orchestra of the musician or peripheral clocks. This orchestra is called 'circadian rhythm'.
As discussed, the central clock is highly dependent on light for its plan. Scientists have found that when there is a change in usual light exposure, even the central clock ticks differently. Such factors that can modify the circadian clock's rhythm are called entrainers. This entrainment is represented by a change in hormonal secretion (cortisol and melatonin) pattern. However, light is not the only entrainer. Peripheral clocks respond to entrainers like meal timing.
Humans are diurnal animals, which means that they are active during the day and rest at night. Therefore, following a regular daily schedule, roughly eating / fasting and waking/ sleeping at standard times, maintains synchrony in our body clocks. However, when the timetable is very different from the standard, the clock desynchronizes, and the physiological responses also change.
Scientists have been observing and reporting a higher prevalence of metabolic disorders in people who do night shifts compared to those who work during standard working hours. Also, people who skip breakfast or eat closer to their sleep are more prone to becoming overweight.
However, what caused this association was unclear initially. Therefore, it was essential to know if such effects resulted from an odd wake-sleep/ eat-fast schedule or they occurred due to higher energy intake or lower activity.
So, several studies were done where one group ate or slept erratically while the other group followed standard sleep and meal pattern. However, both groups ate the same number of calories (known as the isocaloric setting). They also tried changing the meals' size between breakfast, lunch, and dinner (for example, lighter breakfast vs heavier dinner). In such experiments, the group that ate more calories earlier generally showed better health outcomes.
One study reported more weight loss in a group eating early lunch in an isocaloric setting. Similarly, Jakubowicz reported an average of ~5 kg more weight loss in a group that ate 50% calories at breakfast compared to another which ate them at dinner. Similarly, mice with lagged sleep schedules were found to be obesity-prone.
Based on overall evidence, erratic sleep and meal schedules should be avoided. Keeping the daily schedule and circadian clock synchronized is one key factor in weight loss and overall health.
References:
- Garaulet, M., Gómez-Abellán, P., Alburquerque-Béjar, J.J., Lee, Y.C., et al. (2013) Timing of food intake predicts weight loss effectiveness. International Journal of Obesity. [Online] 37 (4), 604–611. Available from: doi:10.1038/ijo.2012.229 [Accessed: 5 September 2020].
- Jakubowicz, D., Barnea, M., Wainstein, J. & Froy, O. (2013) High caloric intake at breakfast vs. dinner differentially influences weight loss of overweight and obese women. Obesity (Silver Spring, Md.). [Online] 21 (12), 2504–2512. Available from: doi:10.1002/OBY.20460 [Accessed: 21 February 2022].
- Johnston, J.D. (2014) Physiological responses to food intake throughout the day. Nutrition Research Reviews. [Online] 27 (1), 107–118. Available from: doi:10.1017/S0954422414000055 [Accessed: 3 September 2020].
