How your gut's circadian rhythm affects your whole body

Story highlights

  • Research suggests the composition and activity of microbiota has a circadian rhythm
  • This may explain adverse health effects of modern life, such as eating at night

We've known that bacteria live in our intestines as far back as the 1680s, when Leeuwenhoek first looked through his microscope.

Yogurt companies use that information in the sales pitch for their product, claiming it can help keep your gut bacteria happy.
The bacteria growing on our skin have also been effectively exploited to sell the underarm deodorants without which we can become, ahem, malodorous.
    Until fairly recently our various microbes were thought of as freeloaders without any meaningful benefit to our functioning as healthy human beings.
    However, that view has changed in a big way over the last couple of decades.
    Interest in, and knowledge about, the microbiota has recently exploded. These highly diverse communities of microbes live in and on us in staggering numbers; researchers now estimate that a typical human body is made up of about 30 trillion human cells and 39 trillion bacteria.
    We now recognize they're essential to our health, participating in many important physiological functions such as digestion and metabolism of foods, and immune responses and inflammation; disruption of the gut microbiota might then contribute to a variety of conditions including childhood asthma, obesity, colitis and colon cancer.
    New research is beginning to show that the composition and activity of the microbiota exhibits a daily, or circadian, rhythmicity, just like we do. This offers one pathway to explain a Pandora's box of possible adverse health effects from aspects of modern life, such as eating late at night or too much electric light after sunset.

    The microbial daily routine

    The microbiota is primarily bacterial but also includes viruses and eukaryotes like yeast; the latter are much bigger and more complicated than bacteria, and have a structure similar to our own cells. The total DNA complement of the microbiota is termed the microbiome, and it's what we study to learn about the inner workings of the microbiota.
    In this field's early days, researchers took fecal samples from people to investigate the composition of the gut microbiome. Later they noticed that defining the microbiome from a sample taken in the morning was quite different from one taken in the evening: The gut microbiota was not static over the span of the day.