Breath, James Nestor’s book: what the science supports

What is Breath, James Nestor’s book, about?

Breath: The New Science of a Lost Art was published by Riverhead in May 2020 and became a New York Times bestseller. Nestor is a journalist, and the book reads like a travelogue: he meets researchers, dentists, yoga teachers, free divers and breathing enthusiasts, and tries most of their methods on himself.

Its centrepiece is a self-experiment. Nestor blocked his nose and breathed only through his mouth for 10 days, then switched to nose breathing for 10 days, and describes how much worse he felt, snored and slept on the mouth days. From there the book builds its case: modern humans have drifted into poor breathing habits, and relearning old ones can help.

The middle of the book is a set of chapters on what to change: the nose, the out-breath, breathing slowly, breathing less and chewing. A final part explores more intense methods and breath holds.

What are the main lessons of Breath?

In our own words, the book’s advice comes down to six ideas:

1. Breathe through your nose, day and night.
2. Breathe out fully, letting each out-breath finish.
3. Breathe slowly: about 5.5 seconds in and 5.5 seconds out.
4. Breathe a little less: lighter, quieter breaths, an idea borrowed from the Buteyko method.
5. Chew more: the book argues that soft modern food has left our jaws smaller and our airways narrower.
6. Use intense breathing and holds sparingly, for specific purposes.

What is the “perfect breath”?

It’s the book’s name for a slow, even breath: about 5.5 seconds in and 5.5 seconds out, through the nose, which works out at about 5.5 breaths a minute. It matches slow-breathing research well. Breathing at about 6 a minute makes your heart rhythm and breathing fall into step (Lehrer & Gevirtz 2014), and the best pace varies between people, roughly 4.5 to 6.5 breaths a minute (Meehan & Shaffer 2024). Try it here.

In 5.5sOut 5.5s

There’s nothing magic about 5.5 exactly. Breathform’s coherent breathing uses 5 in and 5 out, the pace in most studies, and anything near it gives you much the same.

Is Breath by James Nestor accurate?

Here are the book’s big ideas, each checked against the research we trust.

The book’s idea	Our verdict, and what the research says
Breathe through your nose	A sensible default; benefits modest. In one small trial, nose breathing went with lower diastolic blood pressure and more “rest” heart activity than mouth breathing (Watso et al. 2023).
Breathe slowly, about 5.5 seconds	Well supported. Across 223 studies, slow breathing raised heart rate variability (Laborde et al. 2022).
Breathe less, keep CO2 up	Mixed. Breath-hold time didn’t predict carbon dioxide levels (Courtney and Cohen 2008).
Tape your mouth at night	Weak. Across 10 studies with 213 patients, clear benefits in 2, and real risks (Rhee et al. 2025).
Chew more for wider airways	Not assessed. An interesting history, but outside what we can check.

Nose breathing has more going for it than one trial: in brain recordings, breathing through the nose synchronised rhythms in areas linked to emotion and memory, an effect that faded through the mouth (Zelano et al. 2016). And humming raised nitric oxide in the nose 15-fold in a small lab study (Weitzberg & Lundberg 2002). Both are early, interesting findings, not proof of health benefits.

The carbon dioxide story is the shakiest part. Beyond the breath-hold result, a trial in panic disorder found that training people to raise their carbon dioxide and training them to lower it helped equally (Kim et al. 2012). What helped seems to be something both groups shared, such as slow, regular breathing, not the gas itself. We look at this in detail in CO2 tolerance and the BOLT score.

In short, the slow-breathing and nose-breathing advice stands up; the bigger health claims need more evidence than the book gives them.

Does mouth taping work, as the book says?

The evidence is weak. Nestor recommends taping the mouth at night to keep breathing nasal. Since the book came out, two reviews have looked at the research. One found clear improvements in sleep apnoea measures in only 2 of 10 studies, and warned of a “potentially serious risk of harm” for people taping without checks (Rhee et al. 2025). Another found little consensus on its benefits (Fangmeyer et al. 2025).

If your nose is blocked, or you snore or wake tired, see a doctor before you tape. The full picture is in is mouth taping safe, and the case for the nose in nose breathing vs mouth breathing.

What did critics say about Breath?

Most reviewers enjoyed it: it’s curious, warm and practical, and it got a lot of people thinking about something they do about 20,000 times a day. The criticism was about evidence. Writing in The Spectator, Kate Womersley said the book “relies on too much anecdotal evidence” and makes claims bigger than the studies behind them, while praising its practical advice.

That’s a fair summary from our side too. Stories make the book a pleasure; they’re also where it overreaches.

What’s changed since the book came out?

Quite a lot, and mostly in its favour on the gentle side. In 2023, a trial of 108 adults found that 5 minutes a day of exhale-focused breathing lifted mood more than mindfulness meditation (Balban et al. 2023). Slow breathing’s effect on heart rhythm is now among the best-documented findings in the field (Laborde et al. 2022), summed up in the benefits of slow breathing.

Other research has cooled some claims. The largest trial of coherent breathing so far found it helped stress and mood, but no more than a placebo breathing practice (Fincham et al. 2023). And both mouth-taping reviews above have come out in the last two years.

So: the gentle core of the book has aged well; the big promises haven’t caught up.

How well each breath is studied

• Coherent breathingWell studied
• Humming bee breathSome evidence

Every study on this page (12)

• Lehrer & Gevirtz, 2014: Heart rate swings most at around six breaths a minute; this review says a blood-pressure reflex is the likeliest reason.
• Meehan & Shaffer, 2024: In two small studies at six breaths a minute, breathing out longer than in made no difference to heart-rhythm measures.
• Watso et al., 2023: In 20 young adults, breathing through the nose rather than the mouth slightly lowered blood pressure and raised heart-rhythm signs of calm.
• Laborde et al., 2022: Across 223 studies, slow breathing raised heart-rhythm signs of calm, during practice and after, though that alone doesn't prove a health benefit.
• Courtney and Cohen, 2008: In 83 adults, breath-holding time measured the Buteyko way did not predict resting end-tidal carbon dioxide, contrary to Buteyko’s claims.
• Rhee et al., 2025: A systematic review of 10 studies (213 patients) found statistically significant improvement in sleep apnoea markers in 2 studies, no difference in others, and a potentially serious risk of harm from indiscriminate mouth taping.
• Zelano et al., 2016: In a small study, natural nose breathing paced the brain's emotion and memory areas, and recall was sharper on the in-breath.
• Weitzberg & Lundberg, 2002: Humming raised nitric oxide in the nose 15-fold compared with breathing out quietly, in 10 healthy people; health effects weren't tested.
• Kim et al., 2012: In a randomised trial of 74 people with panic disorder, breathing training to raise carbon dioxide and training to lower it both reduced panic severity.
• Fangmeyer et al., 2025: A scoping review of 9 studies of nocturnal mouth taping found markedly heterogeneous research and little consensus on its benefits.
• Balban et al., 2023: Five minutes a day of cyclic sighing lifted mood a little more than mindfulness meditation, in 108 adults.
• Fincham et al., 2023: In 400 UK adults, four weeks of slow coherent breathing did no better than a faster placebo breathing practice; both groups improved.

Where should you start if the book inspired you?

Where it’s strongest: slow, quiet breathing through your nose, a few minutes a day. History in Breathform shows the days you’ve done it, if that helps the habit stick. Leave the tape and the long breath holds for now. A soft hum on the out-breath makes it easy to keep the breath slow, and it’s quiet enough to do anywhere.

Questions people ask

What breathing exercises are in Breath?

The book closes with a set of methods drawn from its chapters, from slow, steady breathing and gentle nose-breathing practices to more intense techniques. The one most readers keep is the slow, even breath of about 5.5 seconds in and 5.5 out, which you can follow on this page. We’d treat the intense methods and long breath holds with care.

Is mouth taping safe?

For some people it may be harmless, but the evidence is thin and the risks are real if your nose is blocked or you might have sleep apnoea. A 2025 review of 10 studies found clear benefits in only two. If you snore or wake unrefreshed, see a doctor before taping anything. More in is mouth taping safe.

Is it true that most people breathe the wrong way?

There’s no good count of how many people breathe badly. Some patterns are real and common: breathing through the mouth when the nose is blocked, fast, high breathing when stressed, and over-breathing during anxiety. Most people don’t need fixing, just a few minutes of slower breathing now and then. How to breathe properly covers the everyday basics.

Is Breath by James Nestor worth reading?

Yes, if you enjoy narrative science: it’s lively, curious and full of people and places. Read it as an introduction rather than a manual. Its slow-breathing and nose-breathing advice holds up well; its bigger health promises need the footnotes. Keeping this page’s scorecard beside you is a good way to enjoy it without overreaching.