The braingym: Does mental exercise burn calories?

17/10/2026, Dr. Anne Bakhit

You can feel quite exhausted after a period of intense mental effort. A few hours of serious studying can also leave you feeling hungry. Does this mean your brain actually consumes a large amount of calories? And, as a follow-up question: does deep thinking help you stay slim?

Let’s break it down. The brain acts like a computer—complete with hardware and software—that runs 24 hours a day. Whether we are awake or asleep, brain activity continues. But what about the intense effort required for work or during an exam—and why do we feel hungry afterwards? Thinking hard certainly consumes a lot of energy; wouldn't it be a huge bonus if it also helped us lose weight? If you don’t feel like going to the gym, could you just solve a Sudoku puzzle or play a brain game on your phone instead? Does it really work that way?

It is true that our brain consumes a significant amount of energy—anywhere from 20 to as much as 60 percent of our total energy expenditure, depending on the situation. For this reason, the brain is sometimes referred to as a "selfish" organ.The brain takes priority over all other organs. This is an absolute necessity; if the brain stops functioning, the rest of the body ceases to function as well. Consequently, the brain has various ways of securing the sugars it needs. If the supply from food drops, the brain can, for instance, send a signal to the liver, prompting it to release more sugar. This provides the energy the brain needs to keep working. The brain never rests.

Unfortunately, however, a brain engaged in intense thought does not consume significantly more energy than a brain that is simply resting lazily on the couch. While the brain does consume a great deal of energy, it continues to do so even when you aren’t engaged in intensive mental work.If you are simply sitting quietly in a chair, without focusing on anything in particular, your brain is still hard at work: observing your surroundings, maintaining your balance, controlling your muscles, and processing your thoughts—which never truly come to a complete standstill. In other words, even in a state of relative rest, your brain remains busy.

A difficult mathematics exam might require some extra mental effort, but in terms of energy expenditure, it makes little difference. Yet, as mentioned, intense thinking can leave you feeling quite exhausted—and even hungry. How does that work?A mental snack break: During an exam, your brain is subjected to a high volume of stimuli. Eventually, it reaches its limits and requires time to recover.

Throughout the day—especially when you’ve been doing a lot of thinking—waste products accumulate in the brain. These substances are cleared away while we sleep or during a walk in nature. In short, relaxation helps—literally reducing stress and lowering your adrenaline level. In practice, however, people often feel the urge to eat.

Does thinking, then, actually make you gain weight? The hunger you might feel after mental exertion may not be a result of physical exhaustion, but rather a form of ‘mental saturation'. So intense thinking might be more likely to lead to weight gain rather than weight loss. This idea is supported by a 2008 Canadian study. Researchers asked participants to read a text for 45 minutes and then type a 350-word summary. On another occasion, the test subjects were asked to do nothing for 45 minutes. Afterward, their calorie expenditure was measured in both instances. 

It turned out that, following the cognitive task, the test subjects had burned approximately 3 kilocalories more than they had while doing nothing. That is slightly less than 1 gram of sugar—not exactly a earth-shattering difference, though one might argue that every little bit helps.However, this was not the full extent of the study. Following the sessions, the test subjects sat down to eat. And here is the kicker: after the cognitive test, the participants consumed, on average, 230 kilocalories more. That is equivalent to about 58 grams of sugar—roughly fourteen sugar cubes. Now, that is a significant difference.

So, I’m afraid I have to disappoint you: thinking is no substitute for the gym. In fact, if you’re not careful, it could even have the opposite effect. Still, we wouldn’t recommend giving up thinking altogether—after all, a healthy dose of mental challenge offers plenty of other benefits.