Our bodies’ internal circadian clock may be profoundly important to our health, especially as it pertains to our metabolism. Research has shown that people who have altered sleep cycles, like those who work the night shift, are at an increased risk for diabetes, obesity, and metabolic syndrome. Researchers from the University of Chicago recently investigated how the microbiome may be involved in the complex relationship between disruptions to circadian rhythms and obesity. They published their results in the journal Cell Host & Microbe.
The human circadian clock is regulated by a few organs in our bodies, including the brain, the liver, and is now evident from this study, the microbiome. The researchers first measured gene regulation by the liver in germ free mice and normal mice. They discovered that many of the genes that had daily rhythmic variations had their rhythms greatly affected by the presence and absence of bacteria in the gut. They then subjected these mice to high fat and low fat diets and learned that, unsurprisingly, the high fat diet led to obesity in normal mice. Surprisingly though, the high fat diet did not lead to obesity in germ-free mice. Interestingly, many of the liver genes that were expressed rhythmically by the gut also had their rhythms affected by diet, with different genes having their expression altered depending on the diet.
The researchers then discovered that the populations of bacteria that comprise the microbiome also exhibited rhythmic variations throughout the day. These variations did not necessarily relate to time of feeding either, as mice that were fed constantly throughout the day still experienced these variations. Moreover, they realized that specific metabolic functions also changed rhythmically throughout the day, such as utilization of specific carbohydrates, and that a high fat diet would quell these rhythms.
The scientists then measured certain metabolites produced by the microbiome, such as short chained fatty acids (SCFAs), and saw these were also produced rhythmically throughout the day, which may be, but is not entirely, related to the differences in microbiome populations. Metabolites rhythms were also affected by diet. For example the high fat diet decreased SCFA rhythms. The scientists then determined that these metabolites have a direct impact on the cycling of liver circadian genes. This means that the microbiome metabolites and the human liver combine to contribute to our circadian clock.
The researchers go on to hypothesize that consuming a high fat diet disrupts our natural circadian rhythms, which leads to a lower metabolic state and results in obesity. This hypothesis extends to the germ free mice which did not become obese regardless of diet; that is, they did not have a disrupted microbiome to alter their rhythms. Ultimately, the healthiest and strongest circadian rhythms belonged to the normal mice eating normal food.
We have written before about how jet lag can lead to microbiome changes that cause obesity. This paper, in addition to the one described above show how our natural clock and the microbiome’s natural clock work in conjunction to regulate our metabolism. Our circadian rhythms are not something which many people associate with the microbiome, but over time complex systems like this evolve. While this paper may not make someone change his or her behavior, it may make him or her think twice before pulling an all-nighter or having that midnight snack.