The Science of Your Gut Sense & the Gut-Brain Axis | Dr. Diego Bohórquez

KEYPOINTS

• 01

  Gut hormone cells turned out to be wired to nerves

  The gut lining is a single layer of epithelial cells. Scattered among them, at roughly 1 per 1,000, are enteroendocrine cells, named by German physician Friedrich Feyrter in 1938 and long thought to signal only by releasing hormones. In 2015, Bohórquez's group reported that roughly a third to two-thirds of them make direct contact with nerves.

• 02

  A 'neuropod' reaches out like Adam's hand

  Some of these cells grow a long arm with a little 'hand' at its base, which Bohórquez compares to Michelangelo's Adam reaching toward God. After describing it with an unwieldy 'axon-like pseudopod basal process', he coined 'neuropod'. In a dish, isolated gut cells and sensory neurons found each other within hours and re-formed the circuit, which he first saw in June 2012.

• 03

  One synapse separates your gut from your brainstem

  Using a rabies virus engineered to jump just one connection, the lab found label in the nodose ganglion, the vagus nerve's cluster of cell bodies just below the neck, and in the brainstem. That makes it a fast, mostly subconscious line. Hormones act over minutes to hours; this transmission works in milliseconds.

• 04

  The gut senses almost everything you eat

  Cells differ by location: sugar sensing is concentrated in the upper small intestine, while fiber and fermentation products such as butyrate and propionate are sensed in the colon. Bohórquez expects receptors will be found for nearly everything we eat, along with stretch and temperature; the esophagus brings hot coffee to body temperature within seconds.

• 05

  One glucose molecule is read in layers

  Glucose activates the sweet receptor T1R3. Sodium-glucose transporters then depolarize the cell, and metabolizing the glucose into ATP depolarizes it further. The cell releases glutamate onto the vagus within milliseconds, acting on fast ionotropic and slower metabotropic receptors. A neuropeptide follows to complete the experience of 'I got sugar'.

• 06

  Silence the gut cells and mice can't tell sugar from sweetener

  Mice normally pick sugar over a noncaloric sweetener such as stevia, by the second day within about 90 seconds. When the lab used optogenetics to switch off neuropod cells in a small stretch of intestine just past the stomach, the mice became 'blind' to the difference. Switching the cells on made mice treat sweetener, or even plain water, as if it were sugar.

• 07

  Gastric bypass rewires cravings, not just capacity

  At Bohórquez's first Thanksgiving, a woman told him she lost about 40% of her body weight within six months, from around 300 pounds. Her diabetes resolved within a week, and sunny-side-up egg yolks went from nauseating to craved. He says food-choice changes after bypass were first reported clinically around 2011, and that patients' risk of alcoholism rises roughly two- to sevenfold.

• 08

  GLP-1 works on a slower clock

  Asked about GLP-1 drugs such as Ozempic and Mounjaro, Bohórquez explains that gut cells release GLP-1, mainly in response to sugar, onto vagal nerve endings. GLP-1 also acts in the brainstem to reduce appetite. The millisecond signals shape choice and how food feels; hormones like GLP-1 govern how much you eat and when hunger returns, roughly every four hours.

• 09

  Protein is tracked closely

  Bohórquez describes recent animal work: when protein is removed entirely from a diet, the gut detects it and animals stop eating it, unless it is rich in fermentable fiber that lets gut microbes make essential amino acids. When protein is merely low, animals eat more to compensate. This fits Stephen Simpson's protein leverage hypothesis; protein is the most satiating macronutrient. Bohórquez flags the gut-cell link as not yet published.