Chess Grandmasters Do Not Burn 6000 Calories Per Day

A Note on the Production of Facts

I work on metabolism and have some interest in neurons, so I have on several occasions run into the claim that chess grandmasters burn 6000 calories per day during tournaments. I found this implausible and decided to investigate where it came from. While I am not the first person on the internet to express skepticism of such a large number, nobody seems to have worked out the precise source of the claim. I assumed when I dug into it that I would find a specific methodological error. But while methods enter the story, the real problem is that the number was completely made up.

As far as I can tell, the "patient zero" that caused this claim to become so widespread is this 2019 ESPN article:

Robert Sapolsky, who studies stress in primates at Stanford University, says a chess player can burn up to 6,000 calories a day while playing in a tournament, three times what an average person consumes in a day. Based on breathing rates (which triple during competition), blood pressure (which elevates) and muscle contractions before, during and after major tournaments, Sapolsky suggests that grandmasters' stress responses to chess are on par with what elite athletes experience.

This story was then picked up by many outlets, such as CNBC, Men's Health, Inc, GQ, Marginal Revolution, and Joe Rogan.

So the claim came from Robert Sapolsky. However, a Google Scholar search turned up no primary literature from him on the topic. Fortunately, someone on Reddit was also curious and shared an email from Professor Sapolsky explaining the number. He first references a footnote from his 1994 book Why Zebras Don't Get Ulcers:

The definitive study on chess players was carried out by the physiologist Leroy DuBeck and his graduate student Charlotte Leedy. They wired up chess players in order to measure their breathing rates, blood pressure, muscle contractions, and so on, and monitored the players before, during, and after major tournaments. They found tripling of breathing rates, muscle contractions, systolic blood pressures that soared to over 200—exactly the sort of thing seen in athletes during physical competition. See the original report, Leedy’s thesis, “The effects of tournament chess playing on selected physiological responses in players of varying aspirations and abilities” (Temple University, 1975) or their brief report (Leedy, C., and DuBeck, L. 1971. Physiological changes during tournament chess. Chess Life and Review, 708). In a telephone conversation, DuBeck also tells the story of the international match in the early 1970s between grand masters Bent Larson and Bobby Fischer, in which the former had to be given antihypertensive medication in the middle of his losing match; his blood pressure remained elevated for days afterward. And for that special chess fan out there who just can’t get enough of this subject, may I suggest as the perfect gift a copy of Glezerov, V., and Sobol, E. 1987. Hygienic evaluation of the changes in work capacity of young chess players during training. Gigiena i Sanitariia 24, in the original Russian.

This doesn't say anything about calories, though the "tripling of breathing rates" matches part of the ESPN quote. He goes on:

The figure of 6K calories/day is an extrapolation that DuBeck generated, based on those measures and the typical duration of tournaments. Obviously, it's a pretty soft, squishy number. I'd asked the ESPN people to mention that the 6K was an indirectly derived measure, the number of calories shouldn't be presented as gospel, so if they were going to cite the 6K, they should cite these caveats as well. But I guess the caveats didn't make the editing process...

Hope that helps.

Robert Sapolsky

So the source must be in Leedy and Dubeck's work. Leedy's thesis looked at physiological parameters in chess players in a mock tournament. The subjects were 11 chess players with USCF ratings from 1329-1921. For comparison, the title of grandmaster requires a minimum rating of 2500. So there were no grandmasters in the study. Among other things, they measured breathing rate during the games using impedance pneumography. This technique essentially measures the frequency at which your chest goes up and down. Unlike with bona fide respirometry, you can't use this "breathing rate" to infer caloric expenditure, since you don't actually know how much O2 or CO2 is being exchanged. Chest motion can also occur for reasons other than breathing. This is usually managed by making the subjects remain still, but measurements during a chess match will necessarily have contributions from postural adjustments and gameplay.

Their magazine article in Chess Life and Review has this line:

For some, the breathing rate was momentarily above 40 breaths per minute as compared with a normal resting rate in the neighborhood of 14 breaths per minute.

This is presumably the source of the "tripling", as 40 is slightly under 3 times 14. However, note that they say "momentarily". This is because they took the maximum estimated breathing rate over all 10 second intervals measured during the tournament. There was no description in the methods of any attempt to filter out the contribution of other movements to the signal, making the maximum value meaningless. Furthermore, the "normal resting rate" of 14 breaths per minute is taken from a different study. The control breathing rate under non-game conditions in their study is actually 16.53 breaths per minute. The average breathing rate during games went up only 14-18%, nowhere near triple. The important distinction between maximum and average was lost in the footnote from Why Zebras Don't Get Ulcers.

There were no numerical claims made about calorie expenditure in either the thesis or the article, despite some speculation that chess could make for a good workout. It is of course possible that Leroy Dubeck made the estimate in unpublished work or personal correspondence. However, when I asked him by email, he said he had never done so. This makes sense, since the data does not allow for that sort of extrapolation.

Perhaps the answer is in the Russian paper he cites, and Sapolsky simply misremembered the source? Glezerov and Sobol evaluate the "work capacity" of children aged 13-15 years old using the Ruffier-Dickson index, which is a score based on a combination of heart rate prior to, immediately after, and one minute after doing 30 squats. They measure this index before and after a chess training session, and find essentially no difference.¹ This measurement is not only incapable of telling you anything about the energy expended in a chess game, it also runs counter to Sapolsky’s broader argument that chess has a significant impact on physical state.

Where, then, does the number 6000 come from? Since there is no explicit justification for this number written anywhere, I could only speculate. The key number cited in Sapolsky's book and in the ESPN article is that breathing rate "triples" during tournaments. What I believe happened is that Sapolsky took the statement that breathing rate tripled, and multiplied it by a typical calorie expenditure over an entire day: 3 x 2000 = 6000.

When I emailed him with this hypothesis, his response was

YEs, something like that... [sic]

which I will take as confirmation.

Notably, in the email linked above and in my correspondence with him, Sapolsky insisted that reporters had failed to report his caveats. This sounds reasonable at face value. ESPN and Joe Rogan are not typically considered careful arbiters of scientific truth, while Robert Sapolsky is a tenured professor at Stanford. However, the evidence demonstrates that the reporter was simply accurately reporting what Sapolsky told them. Indeed, the earliest reference I could find to the 6000 calories number was in Sapolsky's 2009 Class Day Speech at Stanford 10 years before the ESPN article, with no caveats:

So you got two humans, and they're taking part in some human ritual, they're sitting there silently at a table, they make no eye contact, they're still, except every now and then, one of them does nothing more taxing than lifting an arm and pushing a little piece of wood, and if it's the right wood and the right chess grandmaster is in the middle of a tournament, they are going through six to seven thousand calories a day, thinking. Turning on a massive physiological stress response, simply with thought...

To summarize: a grad student took physiological measurements of 11 ordinary chess players (not grandmasters). They reported in a summary in a chess magazine that the maximum chest movement rate they measured in a 10 second period was almost three times that of an average measurement from a different study. Robert Sapolsky then cited this thesis in his popular book, dropping the distinction between maximum and average to give a 3X breathing rate. He later took the 3X number and multiplied that by 2000 calories per day to get the number 6000, adding the "grandmaster" rhetorical fluorish along the way. He spread this fact through his own talks at Stanford and through interviews with journalists, who accurately repeated him. When questioned about the source of the number, he then claimed on multiple occasions that the number actually came from someone else, and that journalists had distorted his argument.

Suffice it to say this is unbecoming of such an esteemed professor.

Thanks to Allison Jonjak and Alex Poddubny for feedback.

1. I was unable to read the paper in the original Russian as my knowledge of Russian is limited to arduously sounding out Cyrillic letters. I fed it through an automated translator and then asked a friend who could read Russian if my summary was accurate. He said yes, though I take responsibility for any misinterpretation.