A frequent consequence of taking long-haul flights is jet lag. It is the disorienting feeling of being out-of-sync with your destination, for instance, feeling wide awake in the middle of the night. While fatigue and sleep disruption are the most obvious symptoms of jet lag, fascinating new research reveals that even modest shifts in our daily schedule can throw our internal metabolism into disarray, at least temporarily.
A new study from the University of Surrey and the University of Aberdeen has found that disruptions to our body clock, such as those experienced during jet lag, impact our metabolism—but to a lesser extent than sleepiness and the primary clock in the brain. Led by Professor Jonathan Johnston at the University of Surrey and Professor Alexandra Johnstone at the University of Aberdeen, the research involved a controlled experiment where 14 participants (eight men and six women) experienced a five-hour delay in their bedtime and mealtimes.
Published in the journal “iScience,” the study, titled "Short-term changes in human metabolism following a 5-h delay of the light-dark and behavioral cycle," highlighted that time shifts lead to reduced energy spent processing meals, changes in blood sugar and fat levels, and slower release of breakfast contents from the stomach. However, these metabolic effects were temporary and mostly recovered within 2-3 days of the five-hour delay. This was in marked contrast to the main clock in the brain, plus feelings of sleepiness and alertness, which had not recovered within five days of the five-hour time delay.
The study also revealed that certain metabolic processes are more resilient to time changes than others. For instance, the participants’ resting energy expenditure—how many calories they burned while at rest—remained surprisingly stable despite the scheduled shift. This suggests that some aspects of our metabolism are more firmly “anchored” than others.
One particularly fascinating finding involved melatonin—often called the “sleep hormone”—which is a reliable marker of our internal biological clock. After the five-hour schedule shift, participants’ melatonin patterns gradually adjusted at a rate of about 1-1.5 hours per day. This methodical adaptation demonstrates how our bodies don’t simply flip a switch to adjust to new time zones but rather undergo a careful recalibration process.
The research has important implications beyond just helping us understand jet lag. In our modern world, many people regularly experience “social jet lag”—the misalignment between their natural body clock and social obligations that require early wake times. This study suggests that even these smaller time shifts might have metabolic consequences we should be mindful of.
The findings also highlight why sticking to daily schedules, especially when it comes to regular meal times and sleep patterns, might be particularly important for metabolic health. While our bodies can adapt to schedule changes, repeatedly forcing them to do so might not be ideal. So, while we can’t avoid crossing time zones on long flights, we can at least understand why our bodies respond negatively to jet lag or other significant schedule changes.
(With inputs from multiple news sources)