December 8, 2019


Can fasting help athletes hold their breath longer?

This was basically the question posed to me by my friend, Justin Lee, a world-class freediver and spearfisherman who is already hard at work training for the 2020 World Championships next Fall.

Read Time 5 minutes

Can fasting help athletes hold their breath longer? This was basically the question posed to me by my friend, Justin Lee, a world-class freediver and spearfisherman who is already hard at work training for the 2020 World Championships next Fall.  

Freediving is a sport of diving underwater without the use of a breathing apparatus. There are many different activities that fall under the freediving umbrella—underwater hockey, or “octopush” being among my favorite applications—but all of them favor a particular athlete. Someone who can hold his or her breath longer will have a competitive advantage. And Justin is just such a guy. 

Static apnea (STA) is a discipline in which a person holds his or her breath (i.e., apnea) underwater, and more or less without moving (i.e., static), for as long as possible. In this case, holding your breath longer is the competition. Most healthy untrained people can hold their breath underwater for at least 30 seconds before coming up for air. What may be surprising is that the major limit to holding your breath for an extended period is not due to a lack of oxygen (O2), but to a trapping of the molecule that we release into the atmosphere with every exhalation: carbon dioxide (CO2). In other words, the discomfort you feel when you hold your breath results from the accumulation of CO2, which is perceived by your brain (thankfully) as an early warning sign that you’re not gas exchanging. 

In a small study of 13 elite freedivers, the average breath-hold duration was four minutes and 15 seconds in laboratory settings. Instead of immersing themselves underwater, they laid flat on their backs on a bed. While a four-plus minute breath-hold is remarkable itself, what is noteworthy for our discussion today is what happened to the performance of these individuals under two different conditions. 

In one instance, the 13 participants performed a maximal breath-hold one and a half hours after their first meal of the day. Serving as their own controls, they also performed the same test after an overnight fast, which amounted to 13 hours since their last meal, on average.1 Participants were tested in a weighted order such that seven started with the fasting test, and six with the fed test.

The results weren’t subtle. The average duration of the max breath-hold in the fasting condition (4:41) was 50 seconds longer than in the fed condition (3:51). From a statistical standpoint, it’s not often that you see a p-value less than 0.001 in a study with only 13 people, but that’s what the investigators found after crunching the numbers. Unsurprisingly, the investigators concluded that fasting is beneficial for STA performance in elite divers.

This study raises a couple of questions: 

  1. What is it about the fasting condition that is advantageous for these divers? 
  2. How would a longer fast impact the performance of these divers?

In competitive apnea, a crucial component is minimizing metabolic demands. A lower metabolic rate means relatively less O2 is needed or consumed by the body. The less O2 consumed, the less CO2 produced, and as noted above it’s the rising internal CO2 levels that triggers involuntary muscle contractions of the respiratory system. These contractions are also known as involuntary breathing movements, or IBMs, leading to an urge to breathe that cannot be resisted.

Before I discuss the fasting condition, let me address a couple of things about the fed condition. First, in the study, the participants performed a max breath-hold about one and a half hours after eating a meal containing 500 Calories. There’s a metabolic cost of processing this food for use and storage. If we want to minimize metabolic demands, digesting a meal while performing the event may be part of the reason why the fasting condition resulted in a 22% longer breath-hold. Second, there is something called the diving response, which optimizes respiration by preferentially channeling O2 to the heart and brain, enabling submersion for a longer period of time. The ongoing digestive process and the increased blood and O2 perfusion to the gut after a meal may hamper the diving response. It’s possible that one key advantage of the fasting condition is that it eliminates the disadvantages of attempting a max breath-hold in the fed condition. Studying this question using longer fasts might allow us to tease apart the physiology with more clarity. 

Remember, when I’m referring to the fasting condition above, it was a 13-hour overnight fast. Hardly a fast, at all, really. A 13-hour overnight fast is to multiple-day fasting (physiologically) what a drop of water is to a swimming pool. Longer-term fasts, such as a 5-day water-only fast, have a demonstrable effect on other measures of metabolism that may benefit an elite freediver. Typically, for fasts three days or longer, there are changes in thyroid hormones associated with a lower metabolic rate2 Most notably, a drop in triiodothyronine, better known as T3, and an increase in reverse T3, or rT3 for short. and a concomitant decrease in O2 demand. Also, the longer the fast, the higher the production and availability of ketone bodies.

The most abundant of the ketone bodies, beta-hydroxybutyrate,3 Which technically isn’t a ketone. As I explain in a previous post, the reason for this is because the carbon double-bonded to the oxygen in the BOHB molecule is bonded to an –OH group on one side, technically making it a carboxylic acid. or BOHB for short, serves as an alternative fuel source to glucose and free fatty acids, which may also lower O2 demand. A detailed study on the metabolism of ketones by Richard Veech and his colleagues in 1994 showed that giving BOHB to the perfused rat heart in place of glucose increased work output, but decreased O2 consumption. (For more details about this study and its implications, please refer to my previous post on the topic.) In other words, the muscles (in the case of this study, those in the heart) became more efficient, requiring less O2 for the same amount of mechanical work.

Given the above, my hypothesis is that a 5-day water-only fast, or even a 3-day water-only fast, or a Calorie-restricted ketogenic diet (KD-R) will extend the average duration of a maximal breath-hold beyond a 13-hour fasting condition. In the STA study, the participants had lower blood glucose, body temperature, and heart rate before attempting the breath-holds in the fasting condition compared to the fed state, suggesting a minimization of metabolic demands and perhaps a mild state of ketosis. (Unfortunately, BOHB was not measured in this study, though I doubt it would have been elevated.)

The beneficial effects of a 13-hour fast in the context of higher breath-hold durations may be enhanced by prolonging the fast or following a KD-R because it should substantially increase the concentration of BOHB, thus lower O2 demand, increase the time it takes for CO2 to build up, and extend the window of time it takes before the first aforementioned IBMs take hold in elite divers. (The initiation of the first IBM in freediving was coined the physiological breaking point.) 

As the legendary George Cahill wrote in a 2006 paper, “Essentially, any cell challenged by low oxygen availability … should benefit by utilizing [BOHB] in preference to any other substrate…” In that same paper, he illustrated a continual rise in BOHB over the first three weeks into a 40-day fast (Figure 1) from experiments he conducted with his colleagues in the 1960s. No, that is not a typo. Forty days. 

Figure 1. Concentration of ketones and free fatty acids over a 4-6 week fast in males and females. FFA: free fatty acids; B-OHB: beta-hydroxybutyrate; AcAc: acetoacetate. Image credit: Cahill, 2006. 

The longer the fast, the lower the metabolic rate, and the higher the BOHB, resulting in a lower demand for O2. Longer-term fasting induces a lower metabolic rate and the cells are less challenged by low O2 availability because they consume less O2. Those cells also benefit by having and using more BOHB, because it’s the most efficient fuel (in terms of how much oxygen it requires to yield a given amount of ATP), resulting in decreased O2 consumption, relative to glucose or free fatty acids, the predominant fuels in a fed state. And of course this O2 conservation means less CO2 production. This sounds like longer-term fasting can improve performance in elite freedivers. Is there reliable evidence at this point that it does or if there’s an optimal “dose” of fasting for these athletes? No, but I’d sure like to see the experiment done. And I know Justin would, too.

– Peter

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  1. Peter at Hyperlipid has discussed the metabolic chemistry of breath-holding and ketosis.

    I have personally experienced this. I’m 65 and recently diagnosed with breast cancer. During my setup for radiation treatment, I did a breath holding test (DIBH is a new technique for helping move the heart out of harm’s way during zaps.)

    They wanted to see how long I could hold my breath. They came out and stopped the test after two minutes and I was not uncomfortable yet. Let me note that I have not done any swimming or breath-holding since my 20s; I have been low-carb/keto for about nine years.

  2. a breathold test done before eating in the morning could be done at the same time you might take your morning heart rate before you get out of bed. Thats when I would do it. In which case it would need to be factored into the results, as breatholding is hugely affected by heartrate, and resting heart rate is as low as it ever gets first thing in the morning. This seems really obvious to me as a flag to check up on. Certainly there should nt be any p values drawn from the results if those contextual things aren’t being controlled, surely.

  3. Hi,

    Nice article! Here’s a couple of points from a competitive freediver’s perspective.

    The general idea that fasting increases static results seems to be correct. Lately, there have been at least two documented n=1 tests on long fasts before static. 
    Eric Fattah fasted for 21 days, increasing his static result from 7min 31s to 10min 6s. (Link here:
    Freediving world champion Mateusz Malina improved his static from 9-minute range to 10min 40s after a long fast. (Link here:
    The increase in performance seems to be caused mainly by a decrease in metabolic rate.

    About CO2 in freediving, there is some nuance to it. For beginner freedivers, CO2 is indeed the limiting factor, but that’s not the case for high-level competitive divers. Most of the high-level athletes can push their dives so far that the lack of oxygen (leading to a blackout if pushed too far) is the limiting factor. In all cases of long statics, there are several minutes of contractions. In fact, freedivers don’t even want to lower the CO2 levels too much. If you have less CO2 in the blood, the Bohr effect causes the O2 to get stuck in the hemoglobin, which causes you to blackout earlier. So, usually, a higher amount of CO2 delays the effects of hypoxia and improves the result. In static apnea, there is a tradeoff because with higher CO2, the contractions start earlier, and since contractions are muscle work, they consume oxygen. Therefore, optimal static performance is about finding a balance between delaying contractions and still having enough CO2 in the end. Delaying contractions can be done with slight hyperventilation, warm-ups (doing several statics in a row), and changing the respiratory quotient by fasting. Typical static strategy of an elite freediving athlete includes 8+ hour fast to move the respiratory quotient a bit more toward fats, doing some warm-ups, either with empty or full lungs, and some hyperventilation (from none to a lot, depending on athlete). However, there are other strategies, like no-warm-up, which count on earlier contractions and stronger mammalian dive reflex.
    Fasting works for static apnea. Still, there are many other freediving disciplines, i.e., diving for maximum length in pool (dynamic apnea without fins, with a monofin, or with bi-fins), or diving for maximum depth in the ocean (again, in several different disciplines) that require muscle work. Because of the mammalian diving reflex, blood flows away from muscles into inner organs and the brain during the dive, causing muscles to work mostly anaerobically, leading to lactic acid build-up. Therefore, carbohydrates are needed in other disciplines than static. In dynamic disciplines, you don’t want to delay the contractions, because earlier contractions strengthen the diving reflex, which is crucial in dynamic disciplines. Dynamic pool disciplines are done nowadays almost always without warm-ups and hyperventilation, to maximize the effect of the diving reflex. In depth disciplines, you might want to do some warm-ups to stay more relaxed on the way down, in order to make the equalization of middle ear easier and to avoid lung barotraumas.

    Personally, I have tested being on a ketogenic diet for a month or so, and my dynamic apnea results dropped over 30%, while static results stayed around the same. Some high-level freedivers have managed to make ketogenic diet work in the depth disciplines. If you manage to work around the lower anaerobic capability caused by the diet, there might be some benefits related to reduced nitrogen narcosis in the depth disciplines. For other disciplines than static, there are slightly different eating strategies used by different freediving athletes. In any case, you don’t want to each just before diving, due to the metabolic cost of processing food. I prefer to eat some carbohydrates 1,5 to 2 hours before a long dynamic dive. Some other top-level divers fast longer, up to 12 hours or so also before other disciplines than static, so that strategy can work too. However, those divers tend to have stronger static performances, suggesting that also their dynamic performances are not done in as anaerobic mode as some other divers.

    For anyone out there interested in testing these things, never freedive alone! Blackout is always a risk, and if you blackout in the water without someone there to pick you up immediately, you will die. Hyperventilation is especially dangerous and can make blacking out very easy. Always dive with a buddy who knows freediving, and take a freediving course.

  4. Did the divers sleep before the meal, or were they also tested after overnight sleep and a 500Kc meal? From what I understand from the design, the controls are quite inadequate. 13h of reduced metabolic activity (sleep) may have something to do with the results.

  5. Thank you, fascinating read! I was curious about the techniques that divers use when they hold their breath for 5 or more minutes and your article was ana eye-opening experience! Also, the fact that fasting makes you hold your breath for longer periods of time sounds so exciting and interesting but so obvious when you lay it all out on paper! Thank you for that! I think that reliable research about optimal fasting “dose” would be unbelievably interesting to read but I can’t see it happening unless a miracle happens because it is sadly not as popular amongst people as a sport to justify spending a lot of money on it. But one can hope! I really wish to try diving at least once in my life, and your article made it even worse, thank you!

  6. Hello,
    I’m a freediver too and also on ketosis and intermitting diet 16/8 hours.
    Thank you for this excellent article and for all the comments below.

    There are so many parameters we can not isolate them easily.
    Par exemple we don’t know the improve in static performace Malina is due to the fasting or the loose of weight.

    Well, in the last year I’ve improved my performance from 7.13 to 7.57. Is due to a fasting, ketogenic diet, intermittent fasting, lose if weight, hard training (co2 tolerance), blood picture improvement, …. ? I realy don’t know.

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