How to Optimize Your Brain-Body Function & Health

The episode opens by extending an ongoing series on sensation. Earlier installments covered vision and hearing, the sensing of light and sound waves. This one turns to what the host calls our sense of self, or interoception: the sensing of the body's "internal landscape." That includes heartbeat, breathing, and the gut, including how full or empty the gut is. It also includes internal chemistry: how acidic things are, and how good or bad a person feels inside. The host says the topic bears on bodily health, brain health, how well or poorly a person performs, and even rates of healing.

The host makes a broad claim for the topic's importance. Interoception, he says, is "right there next to sleep and perhaps one other feature of our health and bodily function" as a main factor in how good a person feels in the short and long term. In his account, neglecting it, like neglecting sleep, means a person "cannot perform well and we will not remain healthy." He uses "sense of self" and "interoception" interchangeably for this discussion. He also describes the topic as sometimes called a sixth sense, alongside hearing, vision, touch, taste, and smell.

The promised payoff is practical. If listeners understand how self-sensing works, the host argues, simple changes could produce "outsized positive effects" on sleep, body composition, mental focus, mood, stress regulation, and recovery from brain and bodily injury. He names nutrition, exercise, and "perhaps even certain things that you take in terms of supplementation" as possible levers. He anticipates skepticism directly: "I don't think that's a hyperbolic statement. In fact, I know it's not a hyperbolic statement." His stated reason is that the body has a system connecting the brain to all bodily organs and the organs back to the brain. This part of the episode makes these claims of benefit but does not yet back them with specific studies.

Before the main subject, the host highlights a recently published study he considers "immediately actionable." It came from the laboratory of his Stanford colleague Justin Sonnenburg and appeared in the journal Cell, which he calls a "very, very high stringency" Cell Press journal. As he summarizes it, people given a high-fiber diet showed less diversity in the gut microbiome, with fewer health-promoting gut bacteria. People who ate a couple of servings of fermented food each day showed beneficial increases in anti-inflammatory markers, which could be traced to greater gut microbiome diversity.

He expects pushback from "folks out there in the nutrition community that really promote high-fiber diet." He defends the findings on method: the data "were looked at in a very unbiased way," using large-scale screens of inflammatory markers. He adds that "There was no specific hypothesis going in, it was purely exploratory." He also limits what the findings mean: "It doesn't mean you shouldn't eat fiber, doesn't mean that fiber's bad." His practical framing is that one or two servings of fermented food a day, "and maybe even ramping up to three or four servings per day," can benefit many aspects of health. He calls one or two servings reasonable for most people, without great cost or inconvenience. He says he will cover the study in detail later in the episode, so this excerpt includes only his summary.

The host also notes that the podcast is separate from his teaching and research roles at Stanford. He describes it as part of an effort to bring science information to the public at no cost to consumers, and he thanks the episode's sponsors.

The anatomical starting point is the tenth cranial nerve, the vagus nerve. The host links its name to "vagabond," meaning to wander, and stresses that it is "not one nerve." It is a vast set of neurons and axons, the wires that let neurons communicate, running throughout the body. He compares it to "a series of superhighways" and to Google Maps, "with alternate routes communicating back and forth."

Signals run in both directions. Neurons in the brain stem, which the host places about three inches deep from the back of the neck, send commands to the organs. These set how fast the heart beats, how fast a person breathes, how fast digestion happens, and even whether the spleen releases immune "killer cells" to fight off bacteria. Those brain stem neurons "don't know what to do" without information coming back up from the heart, lungs, diaphragm, gut, and spleen. In the host's words, "it's a two-way street."

The host sorts what the organs report into two categories. The first is mechanical: pressure or its absence, whether the gut is full or empty, whether the heart beats fast or slowly. The second is chemical: whether the gut is acidic, whether a pathogen is present, and whether the gut has a balance of acidity and alkalinity that "feels right to you." The lungs are one example of chemical sensing. When carbon dioxide rises too high, the lungs register it and send the information to the brain, which then "really encourages you to do certain things" to correct the chemistry.

Mechanical information: pressure or lack of pressure; gut fullness or emptiness; fast or slow heartbeat. Chemical information: gut acidity or alkalinity; presence or absence of a pathogen; carbon dioxide and oxygen levels registered by the lungs.

The host calls the "first principle" of sense of self this: people sense mechanical and chemical information about every organ, "except for one. And that's the brain." He says the brain has no pain receptors and no touch receptors. He describes it as a command center that drives changes in the body's organs but itself moves little, aside from fluid moving within it, "as long as you're healthy."

His evidence comes from brain surgery, which he says he has done and seen many times. The scalp is anesthetized and the skin peeled back, and a bone saw opens a small window in the skull. Electrodes and other devices can then be placed in the brain, for therapeutic purposes, without anesthetizing the brain tissue itself, "because it has no receptors to sense anything." The pressure of a headache, he explains, comes from "receptors that lie outside the brain."

Because the organs must report to the brain, the host argues that their mechanical and chemical state can be controlled "in ways that are very powerful," and that the brain works better when this is done well. He says it is "absolutely clear from data" that a healthy gut with the right acidity and alkalinity, a healthy spleen, and lungs breathing at the right cadence for an activity all improve brain function. He does not cite specific data for this claim in this excerpt. He previews topics still to come: changing gut chemistry to help focus, thinking, memory, and sleep, and changing other organs' chemistry to help the immune system and speed healing from small cuts, bruises, and major injuries.

The first worked example is the lungs and diaphragm. The host corrects the image of the lungs as "two big bags of air." They contain millions of tiny sacs called alveoli, like little balloons that fill and deflate, and more of them means more air capacity. The diaphragm is a dome-shaped muscle below the lungs, like a basketball or soccer ball with most of its air pushed out.

A key detail is that the diaphragm is skeletal muscle, like a bicep or quadricep. That means it can be controlled voluntarily. The host compares it to walking: the legs work fine without conscious thought, but a person can choose at any moment to change their walking cadence. Breathing also involves the intercostal muscles between the ribs. As an aside, he mentions that Bruce Lee was known for very pronounced intercostals developed through bridging exercises.

The host then lays out the sequence. Inhaling fills the alveoli, expands the lungs, and moves the diaphragm down. That gives the heart a little more room, so it gets "physically bigger, not in the emotional sense." The same amount of blood in a larger volume flows more slowly, "Sort of like expanding a pipe." Neurons on the heart called the sinoatrial node send this information to the brain, and the brain signals the heart to speed up. Exhaling reverses the process. The diaphragm moves up, "pushing the plunge on a syringe," and the heart gets slightly smaller, so blood moves faster through it. The brain responds through the vagus nerve by slowing the heart. His summary: "So while inhales speed up the heart, that's the net effect, exhales slow the heart down."