Why can’t we burn more or less calories by working our brain when it already uses a fifth of our daily energy usage?

Question

Hello,

So my question is, our body uses a certain amount of energy through the day and 20% of that is used exclusively by the brain.

Why can’t we increase or decrease the calorie usage of our minds to burn more or less calories?

My own theory is that the brain runs on a base threshold of energy and it normally is around 20% but it doesn’t explain why doing brain teasers/puzzles doesn’t increase it.

And bonus if you can explain how doing extremely challenging problems for any amount of time makes you feel physically tired (such as taking a test).

Edit: there have been a amazing amount of answers while I was asleep (posted this before sleeping for a solid 10 hours), my questions about the brain functionality has been answered

In: 7004

Answer 1

First off, the math isn’t on our side. the brain uses about 20% of your baseline *resting* energy. If I run for an hour, I’ll burn 1,000 Cal, which bumps my daily usage by more than 50% and the brain usage won’t increase.

If I could somehow double my brain’s energy usage for a full 24 hours – **which I can’t** – that would still only be a 20% increase over my normal baseline. If I did it for an hour (how long my run takes), it would be less than a 1% overall increase over baseline – 1/24th of 20%.

As to *why* I can’t increase the brain’s energy: it’s hardwired into how the brain works. The human brain uses a very consistent amount of energy at all times, about 20 Watts. There are 100 billion neurons in the brain, and if you increase activity (i.e. energy consumption) in one brain region, other regions will decrease their average activity to balance the total energy needed. Even if an activity engages 1 billion neurons, the other 99 billion can easily balance out that increased energy with a very small decrease in average activity.

The brain operates separately from the rest of the body in many ways. The blood brain barrier stops a lot of what’s in our bloodstream from reaching the brain. Blood pressure in the cerebrovascular system is even controlled separately from the rest of your body. It’s pretty finely tuned.