Celebrating New Year’s Eve in New York or going on holidays to some Polynesian islands could be a very enticing plan, no doubt, but it may be not so thrilling for your gut microbiota. It appears that this huge community of helpful microbes inhabiting your digestive tract are very sensitive fellows. And if travelling to the other part of the planet can bring on jet lag as a side effect (a very uncomfortable sensation making you feel dizzy, dozy, exhausted), these microbes could “feel” also deeply disorientated by this temporary condition.

A new study with rodents conducted by an Israeli team of researchers that was recently published in the Journal Cell has shown, for the very first time, that gut microbiota follows the circadian rhythm, our internal clock, just as we humans do. When this inner clock is disrupted, it can throw the microbes off, potentially increasing the risk for obesity, diabetes and cardiovascular disease.

Many previous studies had already established links between people with shift work, suffering from disturbed sleep or repeated jet lag and the vulnerability for some health problems including metabolic diseases and even some types of cancer. Until now, however, the exact mechanisms of this relationship were unknown. The findings of this study could be the missing link.

Eran Elinav, senior author of the study, and his team at the Weizmann Institute of Science in Israel discovered that gut microbiota composition and activity vary on a daily cycle. They saw some species of microbes become more active during daylight hours but recede at night, while others behaved in the opposite manner. And they set out to find what would happen if those cycles were disrupted.

To do so, they conducted a study with mice in which they exposed the rodents to jet lag by shifting the lights-on time in their cages over four weeks. As the scientists expected, the animals started eating at random times of the day, which is one of the side effects of jet lag. The researchers also observed that the gut microbiota of the rodents stopped cycling normally and the proportion of species also changed. Furthermore, surprisingly, the mice started gaining some extra weight and having problems with blood sugar levels. They then transplanted that “jetlagged” microbiota in germ-free mutant rodents, which putting on weight and suffering from poor health condition shortly after.

Researchers wanted to check whether these results also happened to humans, so they analysed fecal samples of two volunteers, before and after they travelled from Israel to the USA. The researchers found that the trip altered their microbiota; in particular, volunteers had a higher proportion of Firmicutes, whose overabundance has been linked to obesity. Two weeks after their journey, the volunteers had recovered from jet lag and so did their gut microbiota, which had reverted to their usual cycles.

These findings may open the door to new treatments for people working shifts or suffering from repeated jetlag. These results also have important implications for researchers working with microbiota, because until now they usually compared the gut microbiota of different people using samples collected at a single point of time. In light of these findings, those samples may not be representative, as a person’s microbiota can change dramatically during the course of a day.