Have you ever felt sluggish and uncomfortable after a long-haul flight or a night shift? A new study by the University of Surrey and the University of Aberdeen has shown that disruptions to our internal clock, such as those that occur with jet lag, affect our metabolism – albeit to a lesser extent than fatigue and the master clock in the brain. Led by Professor Jonathan Johnston of the University of Surrey and Professor Alexandra Johnstone of the University of Aberdeen, the study involved a controlled experiment in which participants experienced a five-hour shift in their bedtime and mealtimes.

Even Small Time Differences Can Affect Your Metabolism

The study, published in iScience, highlights that the time shifts result in:

• Lower energy expenditure when processing meals
• Changes in blood sugar and fat levels
• Slower release of breakfast contents from the stomach

However, these metabolic effects were only temporary, largely recovering within 2 to 3 days of the 5-hour time lag. This was in stark contrast to the master clock in the brain, as well as feelings of sleepiness and alertness, which had not recovered within five days of the five-hour time lag.

According to Professor Jonathan Johnston, professor of chronobiology and integrative physiology at the University of Surrey, this research highlights the importance of maintaining a regular sleep schedule, especially in our fast-paced world where long travel and shift work are the order of the day. Even a small time difference can affect many aspects of metabolism, but it now appears that the metabolic effects of jet lag recover much more quickly than the impairment of sleep and alertness. Understanding the effects of circadian rhythms on health can help us make informed lifestyle choices. By optimizing our sleep and eating habits, we can improve our overall well-being.

Jet lag Disorders Associated With Shift Work Can Cause Changes in the Brain that Increase Appetite

Scientists have discovered why night shift work is associated with changes in appetite in a study led by the University of Bristol. The results, published in Communications Biology, could help millions of people who work nights and struggle with weight gain.

Scientists from Bristol and the University of Occupational and Environmental Health in Japan wanted to find out how a “circadian misalignment” – a phenomenon often associated with “jet lag”, in which the body’s biological clock is disrupted – affects the hormones responsible for regulating appetite. In this study, which is common among night shift workers, the international team shows how a circadian misalignment can profoundly alter the brain’s hormonal control of hunger to the detriment of metabolic health. The team focused on glucocorticoid hormones in the adrenal gland, which regulate many physiological functions, including metabolism and appetite. Glucocorticoids are known to directly regulate a group of brain peptides that control appetite behavior, with some increasing appetite (orexigenic) and others decreasing appetite (anorexigenic).

In an animal model experiment that included a control group and a “jet-lag” phase-disaligned group, the team found that misalignment between light and dark cues caused the orexigenic hypothalamic neuropeptides (NPY) of the phase-disaligned group to become dysregulated, leading to increased cravings to eat significantly more during the inactive phase of the day. The team found that the control group rats consumed 88.4% of their daily food intake during their active phase and only 11.6% during their inactive phase. In contrast, the jet-lagged group consumed 53.8% of their daily calories during their inactive phase (without an increase in activity during this time). This was almost five times (460%) more than the control group consumed during their inactive phase. These results show that the timing of food intake matters.

Developing Intervention Strategies

This discovery shows how completely and significantly the neuropeptides are disrupted when daily glucocorticoid levels do not match light-dark cues. However, the authors note that the neuropeptides identified in this study may be promising targets for drug treatments suitable for eating disorders and obesity. Dr. Becky Conway-Campbell, a research fellow at Bristol Medical School: Translational Health Sciences (THS) and senior author of the study, said: “For people who work nights, a reversed body clock can have devastating effects on their health.”

For long-term night shift workers, the researchers recommend getting as much exposure to daylight as possible, engaging in cardiovascular exercise, and eating meals at regular times. However, the brain’s internal messages that increase appetite are difficult to override through discipline or routine. Therefore, researchers are currently developing studies to evaluate rescue strategies and pharmacological agents of intervention. They hope that their results will also provide new insights into how chronic stress and sleep disorders lead to excessive calorie consumption.

Stafford Lightman, professor of medicine at Bristol Medical School: THS and co-senior author of the study, added: “The adrenal hormone corticosterone, which is normally secreted circadian, is an important factor in the daily control of appetite-regulating brain peptides. The study shows that disruption of normal body rhythms, in turn, disrupts normal appetite regulation in a manner that is at least partially due to desynchrony between adrenal steroid hormone production and zeitgeber cues.