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I have read a lot of stuff that says the brain is one of the parts of the body that consume the most oxygen. Is this true? Does that mean when you're thinking hard, you're actually burning a lot of stuff? Is chess considered a sport in this sense?

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According to this article on Livestrong, your brain burns ~20% of your body's energy (pretty impressive, considering it only accounts for 2% of your body weight). Here's a more acedemic source to support this (Thanks matt!). However, according to Livestrong, this is not really due to thinking:

Most of your brain's energy use is dedicated to operating your body -- and not to self-conscious thinking per se.

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I was skeptical of this but I found a confirming study on pubmed. I probably burnt too many calories thinking about that. –  matt Apr 1 '11 at 1:17
    
Thanks for the source, Matt! I've added it to my answer. –  Barbie Apr 1 '11 at 2:06
    
Hi Matt! thanks for the link. Can you point out which part says that the amount of "self-conscious thinking" doesn't really change the energy consumption? Because I couldn't find it. Thanks! –  Louis Rhys Apr 1 '11 at 3:13
    
Hey Louis, I wasn't even considering that distinction when I cited that study. I was focused on the idea of the total energy consumption of the brain. Regarding the amount used by active thinking as opposed to the regulatory functions of the brain this article (which is cited by the SciAm article cited in the LiveStrong post) seems to suggest otherwise. –  matt Apr 1 '11 at 12:16
    
I've modified the answer to reflect the nature of that pubmed citation better. For me the SciAm article isn't evidence against the quote from Livestrong because it takes firing neurons to operate body processes as well as thought. The article doesn't distinguish between neurons dedicated to different tasks. The last paragraph does indicate that visual stimulation may increase energy expenditure, but is it by enough to be considered "a lot"? And is visual perception really considered "thinking"? –  Barbie Apr 1 '11 at 16:41

According to the amazing book: Why Zebras Don't Get Ulcers: An Updated Guide to Stress, Stress Related Diseases, and Coping by Stanford Professor Robert M. Sapolsky:

chess grand masters, during their tournaments, can place metabolic demands on their bodies that begin to approach those of athletes during the peak of a competitive event.

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It sounds like this is due to emotional stress rather than thought (Google Book) –  Barbie Mar 31 '11 at 22:01
    
@Barbie -- You're right, it does sound like that. So is not the brain that is consuming the energy? Perhaps this touches on issues of defining the boundaries between the brain and the body and the boundaries between thought and emotion. –  dsg Mar 31 '11 at 22:19
    
The brain probably consumes some of that extra energy some of that extra energy (I really don't know for sure). But a stress response is systemic, causing stuff like increased heart rate and breathing rate, which consume quite a bit of extra energy. You're right though, there are boundary issues; even if the brain doesn't burn much extra energy itself, it triggers the stress response, so you could say it's responsible for burning those calories. –  Barbie Mar 31 '11 at 23:20

Have you ever seen a fat physicist or mathematician? Go to some university and look for a string physicist who is actually overweight. You won't find many!

So does this prove that the thinking uses a lot of calories? No! But from my experience as a graduate student in astrophysics I can say that thinking hard about a fascinating topic distracts you from eating and drinking. You will simply forget about it. And I believe that is the reason why you might loose weight from thinking.

So thinking doesn't use a lot of calories. But it prevents you from eating to much calories.

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What is true is that the brain uses alot of energy. Relative to its size it's the most energy-consuming of all.

I think this ACNP study would be a perfect place to start.

"Although the brain represents only 2% of the body weight, it receives 15% of the cardiac output, 20% of total body oxygen consumption, and 25% of total body glucose utilization. With a global blood flow of 57 ml/100 g·min, the brain extracts approximately 50% of oxygen and 10% of glucose from the arterial blood."

There are some pretty neat resources on that site, like: Neuro 5th Generation. Covering science once thought impossible, like neurogenesis in adult brains, which could provide useful for people suffering from varioous diseases to the brain.

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