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?
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.
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.
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.
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.