Science Questions

Do brains burn more calories when thinking?

Tue, 22nd Mar 2016

Part of the show Do you burn more calories when thinking?


Haley Walsh asked:

I've noticed I am very tired after a day at uni, even though I am sitting most of the day. I have heard that brains burn approximately 20% of our daily calorie intake, but my question is: Do brains burn MORE calories when you're thinking really hard?





We put this brain teaser to nutritionist Toni Steer...Sleeping Student

Toni - So, itís absolutely right, the brain does require round about 20% of your daily energy intake. The brain relies on glucose; it has to have glucose for energy so unlike other parts of your body, for example, other organs or muscles which can use fatty acids, the brain has to use glucose and it needs around about 120 grams of glucose a day.  Most of the evidence indicates that, actually, you donít see a significant increase in energy consumption with people doing mental tasks.  There have been some techniques where they can scan metabolic activity in different regions of the brain and itís looking at how the glucose moves and is utilised in different regions, and there is some suggestion that when youíre given a specific task you see more metabolic activity and glucose utilisation in different regions of the brain.  But the overall impact of total energy requirement is very minimal and so the idea that if youíre going for a dayís lecture at university you need several chocolate bars, Iím afraid is not true.

Chris - Damn!

Toni - Itís not going to happen.  Maybe the tiredness could be many other factors and, actually, one of them is good hydration.  So tiredness and not being able to concentrate is often about making sure youíre well hydrated.



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The only times I recall losing weight significantly (other than through ill health) were crosscountry skiing (despite eating 5000 calories or more per day) and during Finals.

There is evidence of altered glucose metabolism during periods of mental exercise but it turns out to be very complicated alancalverd, Tue, 13th Oct 2015

Thinking definitely burns calories. Though, I'm not sure how much more it is than when the brain is "resting" (your brain is always working, and most of what it does is not conscious).

I know from first-hand experience that it is much harder to think on an empty stomach/with low blood sugar... chiralSPO, Tue, 13th Oct 2015

That is true, but it does not necessarily follow that this is because the brain needs more energy. Could it not be because the thought processes are interrupted by messages from the body, such as "hello - I'm all of a tremble here"?
MolonLabe, Tue, 13th Oct 2015

That is true, but it does not necessarily follow that this is because the brain needs more energy. Could it not be because the thought processes are interrupted by messages from the body, such as "hello - I'm all of a tremble here"?

That is fair. chiralSPO, Tue, 13th Oct 2015

The answer to this is probably not. When you are awake, all of your brain is being actively used all the time. However, because different parts of the brain are specialised for carrying out certain functions (this is know as being regionally specialised), when you perform a task that requires that function, the corresponding region of the brain increases its activity proportionally. Other, less-recruited, less engaged brain areas drop their activity slightly.

So you can see that, although there will be regional changes in activity to reflect the task being attended to, the overall level of brain activity is roughly equivalent all the time, because we are virtually never doing nothing (you are always thinking about something). chris, Wed, 14th Oct 2015

I also feel harrased after the long day at school or after taking an exam . But , I bet that this is just mental strain. you are emotionally exhausted and you also have an urgent desire to rest in some quiet room where no problems are confronted and no solutions are searched for . however , I will be pleased to find out that , on the contrary,the process of thinkingg does really burns calories .
Lady.Slava, Wed, 14th Oct 2015

This suggests the idea that there might be a negative correlation between being overweight and intelligence. I know quite a few people who are really overweight and really dumb, but not a statistically significant number.

The idea that you (I mean everybody) could lose weight just by thinking is probably brilliant but impractical. If the brain is ticking over at about 12 watts, then it's not going to increase that much when your are pondering quantum electrodynamics, whereas an exercise bike could be expending ten times that much. MolonLabe, Wed, 14th Oct 2015

I think it has something to do with what you are thinking.
The thinking come from problem solving would burn more calories than those from other sample things.
For example, I usually like to entertain foolish ideas and there must hadn't burn any calories!

diethyl, Thu, 15th Oct 2015

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