Jet-lagged gut microbes may promote obesity and diabetes, a new study suggests. The findings indicate that gut microbes may be responsible for some of the health hazards of jet lag and shift work.
Gut microbe communities follow daily rhythms, changing composition and gene functions to a beat set by eating, researchers report in the Oct. 23 Cell. Jet lag or other glitches in the host’s biological rhythms throws the microbes out of sync, the researchers discovered in experiments with mice and people.
When mice’s gut bacteria got off their usual beat, they somehow produced changes in the host’s metabolism that made mice vulnerable to gaining weight and to impaired glucose responses, a hallmark of diabetes. Two people jet-lagged by travel from the United States to Israel had microbial mixes in their feces that were richer in Firmicutes than before their trips. Firmicutes is a phylum of bacteria that has previously been linked to obesity.
When immunologist and microbiome researcher Eran Elinav of the Weizmann Institute of Science in Rehovot, Israel, and colleagues treated jet-lagged mice with antibiotics, the obesity and glucose response problems disappeared. Gut bacteria transplanted from jet-lagged people or mice into mice raised without any bacteria also transferred glucose response problems and the tendency to pack on fat, especially when the mice ate a high-fat diet.
The results back up earlier findings that when you eat may be as important to health as what you eat (SN: 4/10/10, p. 22), says Satchidananda Panda, a geneticist and biologist at the Salk Institute for Biological Studies in La Jolla, Calif.
The study also demonstrates how dynamic microbial communities are, Panda says. Some research has suggested that the gut microbiome a person gets as an infant pretty much sticks around for life. But newer studies have found that dietary changes can dramatically shift gut microbe compositions within a day (SN Online: 12/11/13). This study, Panda says, “shows tremendous shifts in the microbiome in hours.”
Although microbes follow daily rhythms, their fluctuations are not driven by molecular clocks the way many of the human body’s rhythms are, Elinav’s team found. Daily biological, or circadian, rhythms govern the rise and fall of temperature, blood pressure and a host of other body processes. Circadian rhythms also help determine meal times and bed times. Those clocks are set by light and keep a constant, steady rhythm even without resetting each day.
Microbial rhythms, by contrast, need metronomes of regular meal times to stay on beat, Elinav and colleagues found. Mice that lack two genes that are key gears in the circadian clock have no circadian rhythms and eat on an irregular schedule. Their gut microbes had random spikes and declines in abundance of certain bacteria, instead of the predictable shifts seen in mice with functioning circadian clocks. Putting the mutant mice on a feeding schedule restored cycles of changing microbe mixes.
Disruptions of circadian rhythms, such as those produced by shift work, have been linked to obesity, heart disease, diabetes and other health problems. Disturbed microbiome rhythms also seemed to spell trouble for mice in the study.
But don’t count out diet, says Panda. “A high-fat diet is like staying in a state of constant jet lag.” For the people in the study, it’s possible that the microbial rhythms were thrown off as much by what they were eating while traveling as by the time shift. “It’s very difficult to find a fresh salad at the airport,” Panda says.