Breath: The New Science of a Lost Art

The premise of Breath is the kind of thing that sounds like a stunt until you sit with it for a second. Nestor, a science journalist who has already written about dolphins and the deep ocean, notices that he has been breathing badly his whole adult life, and that almost everyone he knows has too. So he goes to Stanford, lets researchers seal his nose shut for ten days, and reports on what happens. That is the opening experiment, and it works as a hook precisely because it is extreme. The book's actual claims are quieter, and in some ways more interesting, than the stunt that gets you to open it.

What Nestor is arguing is that modern humans, specifically industrialized humans, have largely forgotten how to breathe. We breathe through our mouths. We breathe fast and shallow, into our chests rather than our diaphragms. We breathe in air that has been filtered, dried, and conditioned to a degree no previous generation experienced. And he is arguing that these changes have consequences for sleep, anxiety, blood pressure, athletic performance, and general longevity that we are only beginning to measure.

I will say up front that Breath is not a rigorous book. It is enthusiastic journalism, and it moves between well-established respiratory physiology and the claims of breathwork teachers and alternative practitioners with a speed that occasionally left me unsure which footing I was on. That is worth knowing before you start. It is also, in its best moments, genuinely useful, because a few of its recommendations are simple, cheap, and supported by decent evidence.

The ten-day experiment

The nose-plugging study is the spine of the first third of the book, and it is a good piece of journalism because Nestor is a participant as well as a reporter. For ten days he breathes only through his mouth, and researchers monitor him. What follows is a catalog of deterioration. Sleep quality collapses. He develops headaches and brain fog. His blood pressure climbs. He becomes anxious and irritable in ways that surprise him, given that the only variable that has changed is where the air enters his body.

The point of the experiment is to isolate the difference between nasal and oral breathing, and the difference turns out to be larger than most people would guess. Nestor then spends much of the book explaining why, and the explanations are the strongest material here. Nasal breathing does several things that mouth breathing does not. It filters and humidifies air. It produces nitric oxide, a molecule that widens blood vessels and helps with oxygen uptake. It slows the flow of air, which changes the pressure dynamics inside the lungs.

The nitric oxide detail is the one that stuck with me. The paranasal sinuses continuously generate nitric oxide, and breathing through the nose carries it down into the lungs, where it helps oxygen bind to hemoglobin. You do not get this when you breathe through your mouth. It is a small physiological fact with, if Nestor is right, outsized consequences, and it reframes the simple advice to close your mouth as something closer to a technical recommendation.

Why we stopped breathing well

Nestor's account of how this happened is part history and part anthropology, and it is the section where the book is most fun. He travels to talk to people from cultures that breathe differently, including a tribe whose members sleep upright, and he makes the case that the shift toward mouth breathing tracks closely with changes in the human skull and jaw.

The argument, drawn largely from the work of anthropologists like Weston Price and later researchers, is that industrialized diets, and specifically soft processed food, changed the development of children's faces. Jaws grew smaller. Teeth crowded. Airways narrowed. The result is a population that is anatomically predisposed to mouth breathing, which then becomes habitual, which then produces the problems Nestor catalogues. He cites studies of children who were mouth breathers and whose facial structure changed after the habit was corrected, which are striking if you trust the sample sizes.

This part of the book is speculative in places, and Nestor is at his most persuasive when he is describing what people in various traditions actually do rather than when he is explaining why. The observation that many traditional cultures held infants and slept differently from modern Western parents is interesting on its own terms, without needing to bear the weight of a theory about jaw development.

The chemistry of it all

One of the recurring subjects in Breath is carbon dioxide, and this is where the book is most likely to surprise a general reader. The common understanding of breathing is that it is about getting oxygen in. Nestor argues, correctly as far as I can tell, that the story is at least as much about carbon dioxide, and that our instinct to purge the body of CO2 is often counterproductive.

The mechanism he describes is worth laying out because it underpins several of the book's practical recommendations. Carbon dioxide is not merely a waste product. It is what signals your tissues to release oxygen. In a person who hyperventilates, or who breathes chronically fast, CO2 levels drop, and paradoxically that makes it harder for hemoglobin to deliver oxygen where it is needed. The result is a person who is getting plenty of air and still feels short of it, which describes a great deal of modern anxiety.

This is also where the book engages with the Buteyko method and similar approaches that train people to tolerate higher CO2 levels. Nestor is sympathetic but not uncritical, and he tries to separate the physiological core of these practices from the more extravagant claims made for them. Whether he succeeds is debatable, but the effort is there.

The practical translation is that slow breathing, and particularly extending the exhale, is doing more than calming you down in some vague psychological sense. It is changing your blood chemistry in measurable ways. That is a more interesting claim than breathe slowly because it is soothing, and it is the reason I have found myself doing the book's exercises more often than I expected to.

The fringe, and how the book handles it

Breath spends real time with people whose claims sit well outside the mainstream. There are breathwork teachers who describe sessions as comparable to psychedelic experiences. There are practitioners who claim to cure serious illness. There are free divers who do things with their bodies that look impossible. Nestor reports all of this with evident fascination, and this is where a careful reader should slow down.

The free diving material is, to my mind, the most interesting of the fringe sections, because free divers do extraordinary things under controlled conditions that can be measured, and their abilities reveal something real about what trained breathing can do to heart rate, oxygen consumption, and the mammalian dive reflex. It is genuinely impressive. But the jump from there to claims about curing asthma or reversing aging is a jump the book makes more readily than the evidence supports.

I do not think Nestor is being irresponsible exactly. He is clear, at various points, that some of what he reports is anecdotal, and he frequently notes when he is describing a practitioner's claim rather than a study's finding. The problem is tonal. The book moves so fluidly between the credible and the speculative that the credible parts inherit some of the speculative glow, and the speculative parts inherit the credibility of the studies. A more careful structure would have separated them more cleanly.

What you can actually do

The most useful part of Breath, and the part I return to, is the simple advice near the end. Nestor distills a lot of the preceding material into recommendations that require no equipment and no money, and that is a real virtue in a health book, which is a genre crowded with supplements and devices.

The core recommendations are these. Breathe through your nose, including during exercise and sleep. Slow your breathing rate, aiming for something like five or six breaths per minute rather than the typical fifteen to twenty. Extend your exhale so that it is longer than your inhale. And if you snore or wake unrefreshed, take seriously the possibility that your breathing at night is compromised, because the consequences of that are larger than most people assume.

There is a separate strand on holding your breath, drawn from the work of Patrick McKeown and the Buteyko tradition, which involves gradually increasing the length of comfortable breath holds as a marker and trainer of CO2 tolerance. Nestor's treatment is gentle and unsensational, and it is one of the more defensible practical sections in the book.

What I appreciated is that none of this is presented as a cure. The claims are modest. Your sleep may improve. Your resting breathing rate may drop. You may feel less anxious in stressful moments. Those are achievable, and they are worth having, and the book does not need to overreach to make the case for them.

The writing

Nestor is a good writer, occasionally a very good one, and the book moves quickly. He has a reporter's instinct for the telling detail and a novelist's instinct for scene, which keeps what could be a dry subject in physiology from ever feeling like a lecture. The chapters are short and each tends to hinge on a single encounter or experiment, which gives the book a rhythm that suits its subject. You can read it in pieces, which is appropriate for a book about breathing.

The weakness of that style is that it privileges the dramatic. A story about a man who breathed through a monastery and achieved things that sound like folklore is more fun to write about than a carefully designed study with a modest effect size, so the dramatic wins, and the reader's sense of what is established gets distorted accordingly. This is a common problem in science journalism and Nestor is not immune to it.

There is also a certain amount of repetition. The claim that we breathe badly recurs, and recurs, and by the final third the book is circling ground it has covered. I did not mind this much because the material is pleasant to spend time in, but a tighter edit would have made the argument land harder.

Reading it with the right expectations

I have recommended Breath to several people and always with the same caveat, which is that it is best treated as a collection of interesting hypotheses and a few genuinely useful practices rather than as a settled account of respiratory science. If you read it that way, you will probably come away with one or two habits that help you, and a new appreciation for a function so automatic you had never thought to examine it.

If you read it expecting a definitive text, you will be frustrated, because the book is more curious than rigorous and it prefers the interesting story to the well-powered study. That is a real limitation and it matters if you are making health decisions on the strength of what you read. But it is also, in its way, the book's strength. Nestor's curiosity is contagious, and he made me pay attention to something I had been doing wrong for thirty years without knowing it.

The measure of the book, for me, is what happened after I put it down. I started breathing through my nose during runs. I started paying attention to how I slept. I found that when I am anxious, the fastest thing I can do is lengthen an exhale rather than try to think my way out of the feeling. None of that required believing every claim in the book. It required only the small, persistent suggestion that the way I had been breathing was not the only way, and that a better one was available at no cost at all.