Gut Feelings
You have two brains, in case you weren’t aware. One of them is reading this newsletter right now, receiving light from your retinas and sending it to the visual cortex, which resolves it into shapes that are conveyed to the posterior speech area in the left cerebral hemisphere, that then trigger meanings, memories, understanding. The other brain is monitoring mechanical and chemical conditions in your gut and stimulating blood flow, transporting mucus, releasing enzymes, and carefully mixing and propelling food down your digestive tract. It’s also communicating with “you” (if you consider that “you” to reside in your conscious brain) via neurotransmitters like acetylcholine, dopamine, and serotonin. Serotonin, that desirable hormone that makes us feel happy and calm, is produced primarily (95%!) in the gut.
The enteric nervous system is the large set of neurons in the gastrointestinal tract, separate from the brain in our heads but connected to it with the vagus nerve. It can operate independently of the brain and was likely part of us) before the brain or spinal cord evolved. You could think of the human body as mainly a digestive tract, with arms and legs attached to gather food for it, and a head with a lot of intelligence to figure out how.
Given that frame of reference, it’s surprising that we can be so unintelligent about feeding ourselves. Fred Provenza, a behavioral ecologist who studies foraging behavior in goats and other herbivores, wrote a book that’s captivated me recently, Nourishment: What Animals Can Teach Us About Rediscovering Our Nutritional Wisdom. In it, he sets out to demonstrate the ways that animals choose plants to rebalance their nutrient levels and treat disease, and to investigate why we humans don’t automatically do the same thing.
Part of the answer is embedded in the assumptions behind that word, “automatically.” Because we’re used to thinking of animals as basically stupid, operating on “instinct” rather than decision-making, we might not wonder about /how/ they know what to eat. Provenza was able to show through a series of experiments that to some extent, goats also don’t know initially what’s good for them. They have to try something first to find out. It’s the way they feel afterward, or what Provenza refers to as “post-ingestive consequences,” that ultimately teaches them what’s good or bad for them. They just might be paying more attention than we do.
As far as the enteric nervous system is concerned, goats and humans, and even octopuses and worms, aren’t that different. The way a goat feels when it’s bloated and uncomfortable after a meal or has a craving for protein might not be that different from the way we feel. Things begin to go haywire when the food options presented us aren’t the ones that meet all our needs (which is a situation we put domesticated animals in as well) and when our decision-making brain overrides our gut instincts, literally.
It’s still unclear exactly how our enteric nervous system affects the way we feel. The “gut-brain axis,” as its termed, goes both ways. We know that the bacteria in the microbiome have neurotransmitter receptors, so our internal signaling system communicates directly with the tenants in our gut. And the fact that the gut is the producer of so many hormones obviously has an impact on how we feel. There’s evidence that irritable bowel syndrome can cause depression or anxiety disorders, rather than the other way around as was commonly believed. Mice administered probiotics have shown lowered stress responses. Though most of this research is fairly new, it’s already spawned the field of brain-gut psychotherapy, with specialist psychologists who treat the gut by treating the brain, working in tandem with gastroenterologists who start at the other end.
Knowing how much our brain and gut influence each other is fascinating, but it’s still hard to translate that into our daily decisions about what to eat. At the very least, paying attention to how hungry we are is a good idea, since satiety is a sensation that’s mostly produced by the ENS. Improving gut health, by keeping sugar intake low and fiber high, also helps the enteric nervous system function.
Eat what makes you feel good, and if you're going to cryogenically freeze your brain, you better pay for your body too.
What I’m reading
Nourishment: What Animals Can Teach Us About Rediscovering Our Nutritional Wisdom, by Fred Provenza
I can still recall how my understanding changed the day I realized that palatability and preference are not based entirely on cognitive-rational-analytical thought, but also on noncognitive-emotive-synthetic feedback that arises from within a body. The awareness that palatability is unconsciously influenced by cells and organ systems, including the microbiome, stopped me in my tracks. Until then, I’d been trained to think about foraging in a cognitive-rational-analytical sense in terms of the costs and benefits of selecting various foods.
Years later I came to appreciate that the most intriguing part of the tale reveals a dichotomy between two different kinds of rationalities. One has to do with conscious thought and the rational mind, and the other has to do with emotional experiences and the wisdom body. That’s illustrated if you ask a person why they prefer anything from foods to mates to cars. While people can tell you what they prefer, we don’t necessarily understand how their preferences originate. We don’t need to think about that any more than we have to think about which enzymes to release to digest food. The body takes care of that — without a thought.