How nasal breathing affects sleep, stress, performance, and health

Originally published on May 10, 2023

Nasal breathing can affect sleep quality, stress regulation, exercise efficiency, and how you recover from daily strain. In Episode 221 of the WHOOP Podcast, Dr. Kristen Holmes, Global Head of Human Performance, Principal Scientist at WHOOP, speaks with author and journalist James Nestor about what modern life changed in the way humans breathe, why mouth breathing can create problems at night and during training, and which simple drills can shift physiology fast.

Nestor is best known for the bestselling book Breath: The New Science of a Lost Art, which has sold more than 2 million copies. This conversation turns a broad topic into clear, usable advice, from sleep tape and nasal breathing basics to breath cadence, HRV, and the role of carbon dioxide in performance.

To listen to episode 221 in full, head to the WHOOP Podcast on YouTube.

Why does nasal breathing matter for sleep and daily health?

Nasal breathing matters because the nose filters, humidifies, and conditions air before it reaches the lungs, while mouth breathing skips that process. In practical terms, Nestor argues that the pattern you use overnight can shape sleep quality, stress levels the next day, and how well your body restores itself.

Holmes connects that claim to what WHOOP data often shows in real life. When people shift from habitual mouth breathing toward nasal breathing, she says they often see better restorative sleep and fewer sleep disturbances. That lines up with broader WHOOP sleep tracking, where overnight changes in breathing behavior can show up in Sleep performance, Recovery trends, and respiratory rate patterns over time.

A big part of the discussion centers on sleep tape. Nestor makes a narrow point here, not a blanket prescription. He says it is most relevant for people who already mouth breathe at night, often signaled by dry mouth on waking, repeated overnight thirst, or frequent cavities. Preliminary research in people with mild obstructive sleep apnea, including a 2022 study in Healthcare, suggests that mouth taping may reduce snoring and help some sleep-related breathing issues, but it is not appropriate for everyone. People with significant nasal obstruction or breathing disorders should talk with a licensed clinician before trying it.

In the conversation, Nestor also makes a point that many parents and coaches miss: snoring in children is not benign. He describes it as a sign that breathing may already be affecting growth, sleep quality, and daytime function. That is consistent with the larger frame of the episode, which treats breathing as a root-level behavior rather than a wellness add-on.

Nestor puts a concrete number on how common nighttime mouth breathing may be.

"About 65% of the population breathes with an open mouth when they’re sleeping."

If you want to hear Nestor unpack sleep tape, nighttime mouth breathing, and dry-mouth warning signs, listen to the full episode on Youtube.

What you should take away

• Nasal breathing supports sleep by filtering and conditioning air before it reaches the lungs.
• Nighttime mouth breathing may show up as dry mouth, overnight thirst, snoring, cavities, or more fragmented sleep.
• Sleep tape is a tool for some people who mouth breathe at night, but it should be introduced cautiously and only if nasal breathing is comfortable.
• WHOOP can help you see whether breathing changes align with improvements in Sleep, Recovery, and overnight respiratory patterns.

How did modern life change the way humans breathe?

That day to day value makes more sense once you understand Nestor’s bigger argument about why breathing problems became so common. He says the issue is not only habit. It is also structure.

According to Nestor, the shift happened far more recently than most people assume. Looking at ancient skulls, upper palates, sinus cavities, and jaw development, he says humans once had facial structure that better supported open airways and easier nasal breathing. In his telling, the move toward softer, industrialized foods changed chewing demands and facial development quickly, narrowing airways over generations.

The most striking part of his explanation is the timeline. Rather than a change unfolding over tens of thousands of years, he says much of the decline is visible over the last few centuries. That does not mean every breathing issue comes from one cause, but it does frame modern breathing dysfunction as something built into the environment, not simply a failure of willpower.

Nestor also argues that the pattern can start before birth. He says maternal breathing dysfunction and changing facial development may shape the next generation early, which is why he treats breathing as a family and developmental issue, not only an adult performance topic. He is careful to say this does not mean people are stuck. The rest of the episode focuses on retraining the pattern.

In one of the most memorable lines from the interview, Nestor ties the timeline to a specific historical shift.

"Where a lot of this change started occurring was around 300, 400 years ago, when industrialized foods began flooding into cities and the countryside and more."

For Nestor’s full take on facial development, airway changes, and why he believes humans became poorer breathers so recently, listen to the full episode on Youtube.

What you should take away

• Nestor argues that modern breathing problems are partly structural, not only behavioral.
• In his view, softer industrialized diets changed facial development and airway function over the last 300 to 400 years.
• The episode treats breathing as a developmental issue that can begin early, not just a habit adults pick up later.
• Structural disadvantage does not mean breathing patterns cannot improve with training and better awareness.

What happens when you breathe through your mouth instead of your nose?

Once that structural backdrop is in place, the next question is what mouth breathing actually changes in real time. Nestor’s answer is straightforward: for most daily breathing, the nose is built to do jobs the mouth does not do well.

He describes the nose as the body’s first filter. Nasal breathing helps trap particles, adds moisture, warms air, and creates resistance that changes how air moves into the lungs. Mouth breathing exposes the respiratory tract to drier, rougher, less conditioned air. In a city environment, that can also mean more unfiltered pollen, dust, smoke, and other irritants reaching the lungs directly.

The performance piece is just as important. Nestor says nasal resistance is useful, not inefficient, because it helps regulate airflow and maintain healthier carbon dioxide balance. He repeatedly comes back to carbon dioxide, or CO2, as the overlooked variable. Many people think better breathing means moving as much air as possible, but he argues that chronic overbreathing can lower CO2 too much, narrow blood vessels, and reduce efficient oxygen delivery where it is needed.

This is one reason Holmes often connects breathing back to HRV and recovery. Slower, more controlled breathing patterns tend to push the nervous system toward a calmer state, and WHOOP members can often see those shifts in overnight metrics. Related WHOOP conversations on respiratory rate tracking and COVID-19 respiratory trends make the same broader point from another angle: breathing patterns can be unusually stable in healthy states, which makes deviations worth paying attention to.

Nestor summarizes the physiology in a way that is useful for both daily life and training.

"Your nose is controlling the amount of air you can take in and take out, and it does that for a reason, because that allows you to extract so much more oxygen when you have that buffer, that baffle."

If you want to hear Nestor go deeper on nasal resistance, CO2 balance, and why mouth breathing can change oxygen delivery, listen to the full episode on Youtube.

What you should take away

• The nose filters, humidifies, warms, and regulates airflow in ways the mouth does not.
• Mouth breathing can expose the lungs to drier and less filtered air, especially during sleep and routine daily breathing.
• Nestor argues that nasal resistance helps preserve healthier CO2 levels, which supports blood flow and oxygen delivery.
• WHOOP respiratory rate, Sleep, and Recovery trends can help show when breathing behavior is changing over time.

How do you start training yourself to breathe through your nose?

If mouth breathing creates part of the problem, the practical question becomes how to retrain the pattern. Nestor’s advice is to start far below your limit.

He does not recommend forcing nasal breathing during hard exercise on day one. Instead, he suggests building tolerance during low-stakes moments, then progressing gradually. That means practicing while walking, sitting at a desk, or doing other calm activities before trying to carry the same pattern into jogging or harder efforts.

His simplest drill is step based. Walk and breathe in through the nose for four steps, then out through the nose for four steps. If that becomes easy, keep the inhale steady and lengthen the exhale, such as four steps in and six steps out. The longer exhale matters because it tends to be the calming side of the breathing cycle. It can help reduce arousal, settle pace, and make exercise feel smoother.

He also warns that early retraining feels humbling. Capacity often drops first, especially in people who have relied on mouth breathing for years during training. That drop is part of the learning phase. Nestor says this is also where persistent congestion can reveal something structural. If weeks of progressive practice still feel blocked, he recommends consulting an ear, nose, and throat specialist rather than just pushing harder.

That approach lines up with broader breathwork guidance in WHOOP content. The article on the most effective breathwork techniques emphasizes that the most useful drills are often simple, repeatable, and easy to track against physiological data.

Nestor gives the walking version in exact terms.

"Breathe in for 4 steps. Breathe out for 4 steps. Breathe in for 4 steps. Out for 4 steps. Does that feel comfortable? Do you want to push it a little more? You can start extending it."

If you want to hear Nestor unpack nasal breathing progressions for walking, jogging, and early retraining, listen to the full episode on Youtube.

What you should take away

• Nasal breathing retraining should begin during easy walking or seated work, not during maximal exercise.
• A simple starting drill is four steps in and four steps out through the nose.
• Lengthening the exhale first is often more useful than lengthening the inhale.
• Several weeks of consistent practice can help separate habit from structural limitation.

Which breathing drills can change stress, HRV, and performance fastest?

Once the basic pattern is cleaner, short drills can shift physiology quickly. The most practical examples in the episode are coherent breathing and the physiological sigh.

For coherent breathing, Nestor recommends a steady rhythm of about five to six seconds in and five to six seconds out. He notes that taller people with larger lungs may respond well to an even slower cadence, sometimes closer to eight seconds in and eight seconds out. The goal is not maximal air movement. It is controlled, quiet breathing that moves low into the torso and avoids unnecessary effort.

Holmes links that directly to HRV. During the episode, she asks whether lower baseline HRV may sometimes reflect poor breathing patterns, and Nestor agrees that the relationship is real. He says a skeptic can watch the effect in real time by slowing breathing for 30 seconds and observing HRV change. Separate published research supports the stress side of this idea. In Huberman et al. in Cell Reports Medicine, brief structured respiration practices improved mood and reduced physiological arousal, with cyclic sighing standing out as especially effective.

Nestor’s other favorite drill is the physiological sigh. Take one inhale, hold briefly, add a second inhale on top, then let the breath fall out softly. He describes using three or four of these repetitions when stress spikes during the day. Holmes notes that even five minutes of breathing practice can lower perceived stress and anxiety, which matches how WHOOP members often use HRV, respiratory rate, and recovery trends to see whether a calming intervention is actually working.

Nestor gives a measurable claim about the timing.

"Hook them up to WHOOP, have them breathe at the coherent breathing pattern, which is about 5 to 6 seconds in, 5 to 6 seconds out, and then look at the heart rate variability after 30 seconds."

If you want to hear Nestor go deeper on coherent breathing, the physiological sigh, and real-time HRV changes, listen to the full episode on Youtube.

What you should take away

• Coherent breathing usually means about five to six seconds in and five to six seconds out.
• The physiological sigh is a fast stress-regulation tool built from one inhale, a second top-up inhale, and a relaxed exhale.
• Short breathing drills can influence HRV and perceived calm quickly, which makes them easy to test with WHOOP data.
• Quiet, low, unforced breathing is the target, not exaggerated deep breaths.

Can better breathing support exercise performance and weight management?

From there, the conversation moves beyond calmness and into training outcomes. Nestor’s position is that breathing changes are not confined to recovery sessions. They can affect efficiency, pacing, and body composition.

On performance, he says the transition period can be rough for athletes who have long relied on mouth breathing. Capacity may fall at first, and training can feel worse before it feels better. But once the nervous system and respiratory muscles adapt, he says the pattern often rebounds above the starting point. That is the appeal for elite sport: any improvement in efficiency can preserve energy for later in an effort. Holmes brings that perspective from coaching, noting that even high-level athletes sometimes see large gains after fixing airway issues that were disrupting sleep and breathing.

Nestor also highlights CO2 tolerance as an underused marker. He points to the BOLT score, a simple breath-hold measure popularized by Patrick McKeown, as one way to assess how comfortable someone is with rising CO2. His point is not that one test explains everything. It is that many athletes focus on oxygen and lung size while ignoring how breathing mechanics and carbon dioxide handling affect delivery and performance.

The body-composition discussion is more preliminary, but Nestor still offers a clear mechanism. Fat metabolism depends on oxygen, and the byproducts of fat loss leave the body largely through exhalation. The best-known explanation of that process comes from Meerman and Brown in The BMJ, which showed that most fat mass is exhaled as carbon dioxide. Nestor adds that shallow, upper-chest breathing and chronic overbreathing may work against efficient oxygen delivery and healthy blood flow, which could make weight management harder.

He gives the headline number in simple language.

"We do know that 8 pounds of every 10 pounds that you lose comes out through our breath."

For Nestor’s full take on athletic adaptation, CO2 tolerance, and why he connects breathing to fat metabolism, listen to the full episode on Youtube.

What you should take away

• Nasal breathing retraining can reduce exercise capacity at first, especially in habitual mouth breathers.
• Nestor says performance often rebounds after the adaptation period because breathing becomes more efficient.
• CO2 tolerance may matter as much as oxygen intake for understanding breathing quality in athletes.
• Better breathing is one part of weight management because fat metabolism depends on oxygen and fat-loss byproducts are largely exhaled as CO2.

The bottom line

• Nasal breathing supports sleep and recovery by filtering, humidifying, and regulating incoming air more effectively than mouth breathing.
• Nighttime mouth breathing can show up as dry mouth, snoring, cavities, and more fragmented sleep, which makes it worth tracking if recovery feels inconsistent.
• James Nestor argues that modern breathing problems are partly structural, linked to facial and airway changes that accelerated over the last few centuries.
• The nose adds useful resistance to airflow, which may help preserve healthier CO2 balance and improve oxygen delivery efficiency.
• Nasal breathing retraining should start during easy walking and low-intensity activity, not during maximal training.
• Coherent breathing at roughly five to six seconds in and five to six seconds out can shift HRV and calm quickly enough to test in real time.
• The physiological sigh is a simple stress drill that can help reduce arousal in the middle of a demanding day.
• Breathing changes are easiest to trust when they are paired with data, including Sleep, Recovery, HRV, and respiratory rate trends in WHOOP.

Frequently asked questions about things discussed in this episode

How does WHOOP help you see whether breathing changes improve sleep?

WHOOP helps you connect breathing habits to sleep outcomes by tracking Sleep, disturbances, respiratory rate, and Recovery trends across multiple nights. Logging behaviors such as mouth taping or breathwork in the WHOOP Journal can make those patterns easier to compare over time.

What does WHOOP measure that is most relevant to nasal breathing?

WHOOP measures several signals that can reflect breathing-related change, including respiratory rate, HRV, Sleep, and Recovery. Those metrics can help you see whether a shift toward nasal breathing aligns with calmer nights, fewer disturbances, or steadier recovery.

How does WHOOP measure respiratory rate?

WHOOP estimates respiratory rate during sleep from overnight sensor data collected from the band. Overnight measurement is useful because breathing tends to be more stable during sleep than during the day, which makes trends easier to interpret.

What does WHOOP do for tracking mouth taping or other breathing habits?

WHOOP lets you log breathing-related behaviors in the WHOOP Journal so you can compare them against changes in sleep and recovery. That makes it easier to test whether a specific habit, such as sleep tape or a pre-bed breathing drill, is helping in your own routine.

How can WHOOP show whether breathwork affects HRV?

WHOOP can show whether breathwork affects HRV by letting you compare HRV trends before and after a consistent breathing practice. Short calming drills may shift HRV quickly, but the stronger signal usually comes from repeated practice tracked over days and weeks.

What does WHOOP show after a stressful day if you use slow breathing?

WHOOP can show whether slow breathing is associated with steadier recovery after a stressful day by surfacing changes in HRV, respiratory rate, and Sleep quality overnight. The most useful comparison is not one isolated session, but a repeatable pattern across similar days.

How does WHOOP help athletes test nasal breathing in training?

WHOOP helps athletes test nasal breathing by showing how a new breathing pattern lines up with strain tolerance, overnight recovery, and sleep quality during the adaptation period. That makes it easier to see whether an initial dip in comfort is followed by better efficiency and recovery.

If you decide to change how you breathe, WHOOP gives you a practical way to see whether nasal breathing is actually improving your sleep, HRV, respiratory rate, and recovery.