Taking the SAT, crunching through a tough problem at work, or even concentrating while driving in difficult conditions can leave you feeling physically exhausted. But does thinking really hard burn more calories, or does the exhaustion come from somewhere else?
Although the average adult human brain weighs about 1.4 kilograms, only 2 percent of total body weight, it demands 20 percent of our resting metabolic rate (RMR)-the total amount of energy our bodies expend in one very lazy day of no activity. RMR varies from person to person depending on age, gender, size and health. If we assume an average resting metabolic rate of 1,300 calories, then the brain consumes 260 of those calories just to keep things in order. That's 10.8 calories every hour or 0.18 calories each minute.
But the tough question is, how much does that change when you think really hard? Actually, that's not easy to answer and—despite many experiments involving all manner of cognitive tests, biological samples and nutrition experiments—Jabr finds there's no firm conclusion. What does become apparent, though, is that increases in energy consumption are probably far less important than our attitude towards the mental workout:
Completing a complex crossword or sudoku puzzle on a Sunday morning does not usually ruin one's ability to focus for the rest of the day-in fact, some claim it sharpens their mental state. In short, people routinely enjoy intellectually invigorating activities without suffering mental exhaustion.
Such fatigue seems much more likely to follow sustained mental effort that we do not seek for pleasure-such as the obligatory SAT-especially when we expect that the ordeal will drain our brains. If we think an exam or puzzle will be difficult, it often will be. Studies have shown that something similar happens when people exercise and play sports: a large component of physical exhaustion is in our heads.
So, while thinking hard may leave you exhausted and eating might help you feel better, it's not because you're replacing lost calories: in actual fact, you're likely to be comfort eating to make yourself feel happier. [Scientific American]
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