Narrator: Imagine a healthy man deliberately plugging his nostrils with silicone and surgical tape, forcing himself to breathe only through his mouth for ten straight days. Within hours, he begins snoring for the first time in his life, choking in his sleep as his airway collapses. His blood pressure skyrockets, his heart rate variability plummets, and his body floods with stress hormones. This isn't a horror story; it was a real experiment undertaken by the journalist James Nestor. This harrowing ten-day journey into dysfunction serves as the central investigation for his book, Breath: The New Science of a Lost Art. Nestor reveals that this simple, often-ignored act of breathing has been largely misunderstood by modern science, and that by relearning the techniques our ancestors knew, we can profoundly influence our physical and mental health.

Narrator: The book argues that modern humans are the worst breathers in the animal kingdom, and the primary culprit is chronic mouthbreathing. To demonstrate its immediate and devastating effects, Nestor and a fellow researcher, Anders Olsson, subjected themselves to a 20-day experiment at Stanford University. For the first ten days, they breathed only through their mouths. The results were swift and alarming. Nestor’s snoring increased by 4,000 percent, and he developed obstructive sleep apnea, experiencing dozens of breath-holding episodes per night. Both men saw their blood pressure rise into stage 1 hypertension, their stress hormones spike, and their mental clarity dissolve into a fog. They felt miserable.

This experiment vividly illustrates a widespread, yet often undiagnosed, problem. Nestor explains that mouthbreathing bypasses the nose's critical functions of filtering, warming, and humidifying air. This leads to a host of issues, from sleep disorders and high blood pressure to dental decay and cognitive impairment. Historical research, such as the disturbing experiments by Egil Harvold on rhesus monkeys in the 1970s, confirms this. Monkeys forced to mouth-breathe developed crooked teeth, elongated faces, and compromised airways—the same afflictions common in modern humans. The book posits that our collective shift to mouthbreathing is a key driver of many chronic diseases.

Narrator: After the misery of the mouthbreathing phase, the second half of Nestor’s Stanford experiment involved removing the plugs and breathing exclusively through the nose. The turnaround was just as dramatic as the decline. Within days, Nestor’s snoring and sleep apnea vanished, his blood pressure normalized, and his athletic performance on a stationary bike improved significantly. This is because the nose is not just a passive airway; it’s a complex and vital organ.

Nestor details how nasal breathing forces air through the turbinates—bony structures that create a vortex to warm, moisten, and pressurize the air for more efficient absorption in the lungs. More importantly, the sinuses produce a huge amount of nitric oxide, a molecule that plays a crucial role in regulating blood pressure, boosting immunity, and sterilizing the air we breathe. Mouthbreathing provides none of these benefits. The book highlights the work of 19th-century artist George Catlin, who traveled among Native American tribes and observed their universal emphasis on nasal breathing. He noted their robust health, straight teeth, and lack of chronic disease, which he attributed to their cultural practice of keeping their mouths shut, especially during sleep. Catlin’s work, once dismissed, now appears prescient, underscoring that the first step to better health is simply to reclaim the power of the nose.

Narrator: Beyond just breathing through the nose, how we breathe matters immensely. Nestor uncovers that lung capacity is one of the greatest predictors of lifespan, yet most people only use a fraction of their lungs' potential. He tells the story of Carl Stough, a choir conductor who, in the 1950s, was asked to help terminally ill emphysema patients at a veterans' hospital. Stough realized their problem wasn't an inability to inhale, but an inability to exhale. They couldn't clear the stale, deoxygenated air from their lungs. By teaching them to extend their exhalations, he dramatically improved their lung function and quality of life, demonstrating that the key to a fuller breath lies in a complete exhale.

Furthermore, the book dismantles the myth that taking huge, deep breaths is always better. In fact, the ideal is to breathe slowly. Research shows that the optimal breathing rate is around 5.5 breaths per minute, which involves a 5.5-second inhale and a 5.5-second exhale. This slow rhythm maximizes heart rate variability, calms the nervous system, and, most importantly, allows the body to build up a healthy tolerance to carbon dioxide. Contrary to popular belief, CO2 is not just a waste gas. It is the primary trigger that tells hemoglobin to release oxygen into our cells, a phenomenon known as the Bohr effect. Chronic overbreathers and mouthbreathers blow off too much CO2, which ironically leads to less oxygenation of their tissues. Slowing down our breath makes our bodies more efficient.

Narrator: A central question in the book is why modern humans are such poor breathers. Nestor finds the answer not in our lungs, but in our mouths. He explores the groundbreaking research of dentist Weston Price, who in the 1930s traveled the world comparing the health of indigenous populations eating traditional diets with those who had adopted modern, processed foods. He found that within a single generation of switching to soft, industrialized foods, people developed crooked teeth, narrowed dental arches, and obstructed airways.

The reason is a lack of chewing. The hard, fibrous foods of our ancestors required vigorous chewing, which stimulated the bones in the face to grow wide and strong, creating ample room for teeth and large, open airways. Modern soft foods require little effort to eat, and as a result, our mouths have physically shrunk over the last few centuries. This lack of "masticatory stress" is the root cause of the crowded teeth and recessed jaws that lead to breathing problems. Nestor highlights the work of modern orthodontists like John Mew and Theodore Belfor, who are developing techniques and devices to expand the adult palate, demonstrating that it's possible to regrow bone in the face and reclaim our airways, even later in life, by reintroducing the stress of chewing.

Narrator: While the foundation of healthy breathing is to breathe slowly, lightly, and through the nose, Nestor also explores the world of "Breathing+," where intense, occasional bouts of overbreathing can be powerfully therapeutic. He delves into the practice of Tummo, or Inner Fire Meditation, most famously demonstrated by the Dutch daredevil Wim Hof. This technique involves rounds of rapid, forceful breathing followed by extended breath-holds.

Scientifically, this practice consciously stresses the body, flooding it with adrenaline and putting it into a state of sympathetic nervous system arousal. This controlled stress allows practitioners to tap into their autonomic nervous system, which was once thought to be beyond our conscious control. Studies on Hof and his followers have shown they can consciously influence their immune response, fight off infections, and dramatically increase their body temperature to withstand extreme cold. Similarly, techniques like Holotropic Breathwork use intense breathing to induce altered states of consciousness for psychological healing. These practices show that while chronic overbreathing is harmful, using acute, intentional overbreathing as a tool can reset the nervous system and unlock profound resilience.

Narrator: The single most important takeaway from Breath is that how we breathe is a fundamental and tragically overlooked pillar of health, just as critical as diet and exercise. We have become a species of chronic mouthbreathers with underdeveloped faces, and this dysfunction is a major contributor to a host of modern ailments, from anxiety and sleep apnea to hypertension. The book is a compelling call to reclaim our evolutionary inheritance.

The most profound challenge it leaves us with is not a complex regimen, but a simple, conscious choice. It asks us to pay attention to the 25,000 breaths we take each day and to remember the simple, three-word motto championed by George Catlin more than 150 years ago: Shut. Your. Mouth.