Flying across time zones throws your biological activities out of sync with the time of day. Turns out, your gut microbes have circadian clocks too, and when their daily rhythms are disrupted, that might lead to obesity and metabolic problems for you. These findings are published in Cell this week.
Recent studies have found that night shift workers and frequent flyers tend to develop problems ranging from cardiovascular diseases and diabetes to cancer -- but until now, the link’s been unclear. "These findings provide an explanation for a long-standing and mysterious observation, namely that people with chronically disturbed day-night cycles due to repetitive jet lag or shift work have a tendency to develop obesity and other metabolic complications," Eran Elinav of the Weizmann Institute says in a news release.
Elinav’s team analyzed microbes found in fecal samples collected from mice and humans at various times of the day. They found rhythmic fluctuations in the abundance of gut microbes and their biological activities -- oscillations that are controlled by the circadian clock and normal feeding habits of the hosts they reside in.
In healthy mice who were kept in normal 12-hour, alternating light-dark cycles, the team took samples every six hours for two full days. During the dark phase, the bacteria in these nocturnal mice were busy digesting nutrients, repairing their DNA, and growing, Science reports. Microbes did their housekeeping during the light phase: detoxifying, sensing chemicals, and building the tails that help them move.
Gut bacteria in mutant mice with disabled inner clocks didn’t exhibit the same fluctuations in response to either light or dark cycles. But when these bacteria were transplanted into normal mice, the microbes began to show normal rhythms within a week, suggests that the mouse clock controls that of the bacteria, Science explains.
But how do microbes in the gut know when it’s light out? Food. The team exposed mice to varying light-dark schedules and abnormal 24-hour feeding habits, and their microbial communities lost their rhythmic fluctuations and changed in composition as a result. A high-fat diet caused weight gain in jetlagged mice, and they also developed metabolic problems associated with diabetes.
Similarly, two humans who traveled from the U.S. to Israel changed the composition of their gut microbes -- favoring the growth of bacteria linked to obesity and metabolic diseases. And when these microbes were transplanted into healthy mice, the rodents put on weight and showed increase blood sugar. In the human participants, these levels returned to normal as they adjusted with time.