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Bacteria Tell Us What to Eat

August 24, 2014

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.



  1. August 25, 2014 2:28 am

    I’ve heard that we are a set of simpler animals that colonized together to make larger animals–I guess that would require a communication network for required nutrients for those ‘animals’ no longer attached to the mouth….
    Fascinating, as ever, Joan.

  2. August 25, 2014 2:30 am

    Reblogged this on Xper Dunn Is Here and commented:
    Joan Slonczewski, intriguing insights ‘inside’ us.

  3. SFreader permalink
    August 26, 2014 3:09 pm

    Makes sense – there’s quite a bit of scientific/medical literature on antibiotics and nerve damage. The gut is extensively enervated, so kill off the wrong nerves and you could mess up signaling and end up with mood swings, or the wrong mood being communicated.

    An example … Cipro is one of the most cited antibiotics for nerve damage, is the antibiotic of choice for anthrax (remember the D.C. letter scare?), and UTIs. Below is a cut&paste from Wikipedia about side effects but not the mode of action, i.e., whether any gut bacteria are involved:

    “The 2013 FDA label warns of nervous system effects. Ciprofloxacin, like other flouroquinolones, is known to trigger seizures or lower the seizure threshold, and may cause other central nervous system side effects. Headache, dizziness, and insomnia have been reported as occurring fairly commonly in postapproval review articles, along with a much lower incidence of serious CNS side effects such as tremors, psychosis, anxiety, hallucinations, paranoia, and suicide attempts, especially at higher doses.[11] Like other flouroquinolones, it is also known to cause peripheral neuropathy that may be irreversible, such as weakness, burning pain, tingling, or numbness.[49]”

    Would be interesting if this research ends up changing how the Western world takes its meds: move away from swallowing pills toward dermal patches, nasal sprays or needle-free injections.

  4. SFreader permalink
    August 26, 2014 3:17 pm

    That should read ‘innervated’…

  5. September 6, 2014 7:42 pm

    Of course, this just adds to all the problems associated with the abuse of antibiotics. I don’t know what it will take for this country to flat out ban the use of antibiotic in farm animals. Oh, of course, that would mean the factory farms would have to work harder and be a little more imaginative in their breeding practices.

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