Bacteria Tell Us What to Eat
When Brain Plague came out (still my favorite book), reviewers sniffed that microbial aliens were “impossible.” They didn’t ask the microbiologists. Today, the microbiologists are homing in on our gut microbiota. “Take me to your leader” may mean taking a look inside your gut.
Why do we eat what we eat–and why does it “taste good”? Increasing evidence suggests that our gut bacteria, which digest much of our food, put out products that act as neurotransmitters that tell us to eat the foods the gut bacteria want. Known neurotransmitters produced by bacteria include glutamate, glutamine, and agmatine (all nitrogen-containing carbon compounds related to amino acids of protein). But research suggests that a large number of other neurotransmitters remain to be discovered.
How could the microbes do this? Either they might cause signals that increase our desire for foods they can digest; or the microbes could produce mild toxins that make us sick, until we consume what they want. It’s well known that the gut has a huge number of connections to the vagus nerve, which leads straight up to the brain.
One candidate (of many) for bacterial Svengalis is the bacteria that ferment chocolate. Chocolate is one of the most complicated foods we eat, the product of bacteria fermentation to begin with. (You cannot eat cocoa until after the beans have rotted three days in the jungle. The cocoa mass gets sent to Europe for fastidious processing.) It’s a mystery why we even like chocolate, which for humans is largely indigestible. But somehow eating cocoa (or dark chocolate with minimal added sugar) is associated with preventing obesity and diabetes. So maybe our gut bacteria know something that’s good for us.