Why do chess players lose up to 7 kg per tournament?

A Chess Player Can Lose 7 kg During a Tournament. What Happens to Grandmasters? It’s Not About Diets at All

When people hear that a chess player can lose several kilograms during a single tournament, the first reaction is almost always the same: it sounds exaggerated. From the outside, it seems like a grandmaster simply sits at the board, thinks, and moves the pieces. No sprints, no wrestling, no punches, no marathons. But that is exactly where the main misconception lies.

At the highest level of chess, the body works very differently from how it appears from the stands. This is not about “magical fat-burning by the brain,” and certainly not about secret diets. The main factor is prolonged stress over many days, which changes heart rate, breathing, sleep, appetite, and the overall strain on the body. That is why stories about sharp weight loss among elite players keep appearing again and again. ESPN, for example, cited the account that Rustam Kasimdzhanov lost 7.8 kg during the 2004 championship event, and also described how sleep and eating patterns are disrupted for top grandmasters during competitions.

Why Chess Players Lose Weight at All If They Hardly Move

Because a tournament game for an elite chess player is not “quiet sitting,” but several hours of continuous tension. During serious play, players experience increased heart rate, breathing, muscle tension, and anxiety levels. Even if the body looks almost motionless on the outside, physiologically it is functioning in a state of intense stress. Men’s Health, citing ESPN and Stanford researcher Robert Sapolsky, wrote that some chess players during competitions show sharply elevated breathing, blood pressure, and muscle contractions.

But it is important not to swing to the other extreme. This does not mean that chess “burns fat” the same way heavy weightlifting or long-distance running does. The real picture is more complicated: the body uses more energy because of a stress response, while at the same time the player often eats less, sleeps worse, and recovers more poorly. It is precisely this combination of factors that leads to noticeable weight loss. ESPN directly noted that tournament stress changes sleep, increases fatigue, and may contribute to additional loss of body mass.

Where the Story About 7 kg Came From

It did not come out of nowhere. The chess world has long known cases of very sharp weight loss during long and difficult competitions. In an overview of the physical side of champions’ preparation, Chess.com recalled that in 1984 the Karpov–Kasparov match had to be stopped after five months and 48 games, including because of Anatoly Karpov’s rapid weight loss, while Rustam Kasimdzhanov, according to the cited data, lost 7.8 kg during the 2004 World Championship. The same source also says that in major tournaments the total loss for some players can reach 5–6 kg in 10 days.

So the phrase “a chess player can lose 7 kg during a tournament” is not fiction, but it is not a normal standard for every grandmaster either. It is more of an extreme scenario against the backdrop of a very heavy schedule, high stress, and disrupted recovery. It would be wrong to treat it as a universal rule.

It’s Not About Diets — So What Is It About?

The main answer is stress and its consequences.

First, a player’s nervous load can rise sharply during a tournament. Every game means hours of concentration, the pressure of results, fear of making a mistake, and constant inner control. Even after the round is over, the brain often does not “switch off”: many players continue analyzing the position, mentally replaying critical moments, and sleeping badly. ESPN wrote that some grandmasters literally see chess in their dreams, wake up tired, and continue reliving the games they played during the night.

Second, many players lose their appetite. During a tournament it is difficult to eat fully and calmly, especially before a game or between rounds. Chess.com notes that during competitions players often eat less simply because they have no appetite or do not want to overload the body before playing.

Third, sleep breaks down. And that is critical. Sleep deprivation by itself increases fatigue and adds stress to the body. According to ESPN, even one extra hour of lost sleep can make it harder to maintain concentration, which in turn makes the tournament even more exhausting.

Is It True That Chess Players Burn 6,000 Calories a Day?

This is the loudest and most controversial part of the entire topic.

Popular publications really did spread the figure of “up to 6,000 calories a day.” Men’s Health repeated the estimate that some chess players at tournaments may reach such numbers because of an extremely strong stress response in the body. The same article also gave the example of Fabiano Caruana, who, according to ESPN, could lose weight quite noticeably during especially difficult competitions.

But that figure should be treated with caution. There does not seem to be strict direct proof in reliable scientific publications that 6,000 kcal a day is a typical reality for chess players. More likely, this is a loud upper-end estimate for the most extreme cases, which later started being repeated too broadly. Even within the chess community itself, this figure causes strong skepticism, while real observations more often describe not “magical fat burning,” but a combination of increased strain, reduced appetite, and disrupted sleep.

So the honest wording sounds like this: grandmasters really can lose noticeable weight during tournaments, but explaining it with the simple phrase “the brain burns 6,000 calories” is too crude and probably inaccurate.

Why Modern Top Chess Players Spend So Much Time on Physical Preparation

Because elite chess has long understood one thing: the winner is not only the player who calculates variations better, but also the one who withstands the strain better.

Chess.com writes that today’s strongest players pay much more attention to health than in the past. The article mentions running, strength training, tennis, swimming, and other forms of exercise as part of preparation. ESPN and Men’s Health also noted that Magnus Carlsen and Fabiano Caruana work seriously on physical fitness precisely because long matches exhaust not only the mind, but the body as well.

This is an important point. Physical preparation is not necessary because chess is turning into fitness. It is necessary because good physical shape helps a player handle stress, preserve clarity of thought, and avoid falling apart near the finish. In that sense, modern grandmasters have long been thinking almost like athletes in other sports: nutrition, sleep routine, cardio, recovery, blood sugar control, and energy management all become part of the final result.

What Exactly Is Lost — Fat or Something Else?

This is where it is especially important not to oversimplify.

When a person loses several kilograms in a short period of time, it does not automatically mean they have “burned” that much fat. In such rapid weight changes, a major role can also be played by water, glycogen, changes in appetite, sleep deprivation, and general exhaustion. Against a background of stress and irregular eating, weight really can drop quickly, but that does not make the process healthy or desirable. This conclusion follows from the mechanisms described by the sources — reduced appetite, stress, and sleep disruption — rather than from any single magical cause.

That is why the story about chess players losing weight should not be seen as a “weight-loss life hack.” It is not a method, but a side effect of heavy competitive strain.

Why It Still Looks Like “Nothing Is Happening” from the Outside

Because chess is visually deceptive. A spectator sees a calm posture, silence, a table, a board, and maybe just the movement of a hand. But what they do not see is that inside that outer stillness there are hours of constant strain: fighting anxiety, calculating under pressure, controlling emotions, coping with sleep deficit, and being unable to fully relax between rounds.

That is the paradox of top-level chess. From the outside it is one of the most “motionless” forms of competition — and from the inside one of the most draining. That is exactly why stories that grandmasters look exhausted after a tournament are not romantic exaggerations.

Conclusion

Yes, a chess player really can lose 7 kg during a tournament. Such cases have been described in elite chess, and they are not fictional. But this has nothing to do with diets and nothing to do with some miraculous “fat-burning from thinking.” The main reasons are stress, disrupted sleep, reduced appetite, many days of nervous tension, and overall physiological overload.

That is why the modern grandmaster increasingly looks less like an old-school armchair intellectual and more like a very specific kind of athlete: someone who must be ready not only for the variations on the board, but also for the fact that a tournament can hit the body almost as hard as it hits the nerves.