Can the bacteria in our bodies control our behavior in the same way a puppetmaster pulls the strings of a marionette? I tremble to report that this wonderfully creepy possibility may be true.
The human body is, to some extent, just a luxury cruise liner for microbes. They board the SS Homo sapiens when we’re born and settle into their assigned quarters–the skin, the tongue, the nostrils, the throat, the stomach, the genitals, the gut–and then we carry them wherever we go. Some of microbes deboard when we shed our skin or use the restroom; others board at new ports when we shake someone’s hand or down a spoonful of yogurt. Just as on a luxury cruise liner, our passengers eat well. They feed on the food we eat, or on the compounds we produce. While the biggest luxury lines may be able to carry a few thousand people, we can handle many more passengers. Although the total mass of our microbes is just a few pounds, the tiny size of their cells means that we each carry about 100 trillion microbes–outnumbering our own cells by more than ten to one.
It’s important to bear in mind that you can carry this galaxy of microbes around and enjoy perfect health. These microbes, for reasons that are not entirely clear, behave like well-mannered passengers. …
The scientists found that the microbes made the recipient mice hungry–and also made them obese, insulin resistant, and so on.
So here we are. Mice with a genetic make-up that alters the diversity of their gut microbes get hungry, and that hunger makes them eat more. They get obese and suffer lots of other symptoms. Get rid of that particular set of microbes, and the mice lose their hunger and start to recover. And that distinctive diversity of microbes can, on its own, make genetically normal mice hungry–and thus obese, diabetic, and so on.
When I first learned of this work, I asked Knight–with a mix of dread and delight–whether the microbes were manipulating their hosts, driving them to change their diet for the benefit of the microbes. He said he thinks the answer is yes.
This discovery doesn’t just have the potential to change the way we think about why we eat what we eat. (Am I really hungry? Or are my microbes making me hungry?) It also provides a new target in the fight against obesity, diabetes, and related disorders. What may be called for is some ecological engineering.