11/02/2014 08:06 EST | Updated 01/02/2015 05:59 EST

Germs Suffer "Jet Lag" And Can Make You Fat

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Anyone who has traveled across time zones knows the feeling of jet lag. The symptoms are wide-ranging in nature and can include sleep disturbances, a lack of mental clarity and even irritability. The experience is temporary for the most part but can have drastic consequences on quality of life and productivity.

Researchers have been working to understand the reason of jet lag for well over 30 years and have a good sense of the mechanism. The cause is a disruption of a natural phenomenon all life experiences known as the circadian rhythm. In humans, this complex process is carried out at the cellular level in which certain genes with names such as Clock, mPer, and Cry, are expressed in a pattern leading our bodies to feel either awake and alert (day) or tired and restful (night).

When we are stabilized in a certain well-defined and expected cycle of light and dark, our bodies are happy. However, if the timing of that cycle changes such as moving from one time zone into another or changing from the day shift to the graveyard, then the rhythm is disrupted and has to compensate. This can lead to a number of problems ranging from insomnia to metabolic and cardiovascular implications to altered mood.

One particular consequence of an altered circadian rhythm is altered glucose utilization leading to increases in weight gain, obesity and even diabetes. The reason for this has been examined at the molecular level and some paths to problems have been elucidated. But these discoveries do not take into consideration the tens of trillions of bacteria living in the gastrointestinal tract, better known as the microbiome.

Since 2007, when the Human Microbiome Project was initiated, microbial involvement in human physiological function has been studied with several startling results. One of the most important is the role in glucose metabolism and the link with glucose intolerance. When the bacterial ecology is harmonized with a significant proportion of good germs, such as the probiotic bacterium Lactobacillus, the body functions well. On the other hand, if there is a lack of these friendly microbes, a state known as dysbiosis occurs and problems arise.

Though a link between jet lag and microbes may seem logical, no one had actually determined whether it was real. After all, the question of whether germs can suffer from jet lag would have seemed outlandish and not worth investigation. But last week, an Israeli team of researchers dared to ask. What they learned may change the way we all deal with time zone travel.

Before tackling the link, the team first needed to show microbes, like humans, followed a circadian rhythm. The researchers took mice and subjected them to a 24 hour cycle of 12 hours light and 12 hours dark. As they did this, fecal samples were collected and analyzed for their abundance.

Sure enough, the bacteria known to be part of a healthy gut microbiota all exhibited a similar light and dark cycle of metabolism and growth. When the team went looking to find out how this was possible, they found the microbial cycle was entirely dependent on the mouse's circadian rhythm and eating behaviour. In essence, the bacteria were responding to the stimulus of the mouse's daily activities.

The next experiment was simply to change the parameters of the light and dark cycle. The team altered the time by eight hours, akin to travelling from Vancouver to London or changing work shifts, for three days and then returned back to normal for another three. They continued this for four weeks and observed the nature of the gut microbiome in the process.

Not surprisingly, the bacteria were not happy. After four weeks, there was significant dysbiosis as many of the good bacteria had simply disappeared. The bacterial diversity has suffered so extensively, there were secondary effects, such as glucose intolerance, weight gain and loss of lean muscle. Making the situation worse was the irreversible impact of the dysbiosis; even four months after suffering from the time disruption, the mice continued to display these physiological problems.

The evidence in mice suggested the same could happen in humans and the group wanted to see if this was the case. They did a small study involving only two people who were subjected to a similar jet lag experience (in this case from LA to Tel Aviv). Fecal samples were collected before as well as both one day and two weeks after the experience. Sure enough, the same microbial cycle was observed in the control as was the dysbiosis upon disruption of the circadian rhythm. As with the mice, the good germs had disappeared while those causing metabolic problems thrived.

Finally, to prove these metabolic consequences were primarily due to the bacteria, the researchers performed fecal transplantations from affected mice and humans into non-affected mice. In both cases, the recipient mice suffered the same effects. Their metabolisms were disrupted, they gained weight and they experienced glucose intolerance.

The results of the experiments reveal not only the seriousness of jet lag on the body but also the need to maintain a healthy microbiome, particularly during travel or shift work. While the authors did not offer any possible options for therapeutics, the loss of good germs suggests a quicker recovery may be had by taking probiotics such as Lactobacillus. Including them as a part of the diet when on the road or working the graveyard shift may help to reduce or eliminate dysbiosis and maintain a healthy gut.


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