July 28, 2026, 8:05 am | Read time: 4 minutes
When elite athletes travel to international competitions, they face more than just jet lag. Researchers suspect that long flights across multiple time zones could also affect gut flora. A recent review examined how disruptions to the internal clock and changes in the gut microbiome influence each other and what potential consequences this might have for sleep, recovery, and performance. The direction of travel could also be important, by the way.
Long-Distance Travel Affects Multiple Factors
The study suggests that long-distance travel places multiple strains on the body. In addition to sleep disturbances and a temporary misalignment of the internal clock, the composition of the gut microbiome also appears to change. According to the authors, these changes could affect metabolism, inflammatory processes, and recovery—all factors important for athletic performance.
How the Study Was Conducted
The study is a so-called narrative review. Researchers from the Medical University of Wroclaw did not conduct their own study but instead evaluated already published scientific works. This review thus summarizes findings from very different study designs, including randomized studies, observational studies, animal experiments, and laboratory investigations.1
For their research, they used various databases and primarily considered publications from 2016 to 2026. The goal was to summarize the current state of knowledge on the relationship between jet lag, the gut microbiome, and athletic performance.
Jet Lag Also Affects the Gut
Several studies that were evaluated have shown that long-haul travel can significantly impair sleep quality. Among elite cyclists, shorter sleep durations and poorer sleep efficiency were observed in the first 48 hours after long flights. For soccer players, sleep problems persisted for up to five days after a trip from Ireland to Taiwan. Additionally, there are indications of metabolic changes due to a disrupted internal clock. In one study, the level of the satiety hormone leptin dropped by about 17 percent, while insulin and blood sugar levels increased. At the same time, sleep quality significantly deteriorated.
The gut microbiome also reacted to sleep and rhythm disturbances in several studies. Lower amounts of certain beneficial bacterial genera, such as Lactobacillus and Bifidobacterium, were found. In a study with international travelers, 61 percent of participants experienced a decrease in gut flora diversity after the trip. At the same time, potentially problematic bacterial strains were more frequently detected.
Difference Between West and East Flights
It is well known that jet lag is not equally problematic in all travel directions. The current review confirmed this. It found that adjusting to new time zones is easier after westward flights than after eastward flights. The reason is that the human internal clock runs slightly longer than 24 hours on average, making it easier to cope with a lengthened day than a shortened one. Accordingly, adjustment occurs at about 1.5 hours per day after westward travel, while only about one hour per day is achieved after eastward travel.
Studies on elite athletes show that eastward flights, in particular, can be associated with poorer sleep quality, shorter sleep duration, greater fatigue, and performance declines. Analyses from professional sports, including studies from the NBA, Major League Baseball, and Super Rugby, also suggest that the negative effects of jet lag are more pronounced after eastward travel than after westward travel.
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What This Specifically Means
The authors view long-distance travel as a complex strain on the body that may affect not only the internal clock but also the gut microbiome. Short-chain fatty acids, metabolic products of gut bacteria, which could be important for energy supply and muscle recovery, are particularly in focus.
At the same time, the researchers emphasize that many of the previous findings come from animal studies or research outside of competitive sports. Therefore, further research is needed to better understand the practical implications for athletes.
Strengths and Weaknesses of the Study
A strength of the work is that it brings together findings from chronobiology, microbiome research, and sports science, providing a comprehensive overview of a still little-studied topic.
Since it is a narrative review, the literature evaluation was not conducted according to the strict criteria of a systematic review. Additionally, many of the discussed mechanisms come from animal studies, while the available human studies were often small and mostly examined specific groups, such as male endurance athletes. Differences in diet, training, and individual microbiome composition further complicate interpretation. Therefore, large long-term human studies that capture microbiome, metabolism, and performance together are still lacking. The authors also state that they have no conflicts of interest.