Conservation of mass and energy, baby. Thoughts don’t get created from nothing!
I’m being absolutely serious here. Though thoughts aren’t matter, and thus don’t use up mass/energy, the whole process surrounding them does. It’s brain activity and, as odd as it seems, that also requires you to be well-fed to work on maximum capacity. Thinking uses up energy.
This really hit me very clearly during my internship. I sat in my chair all day, performing physically non-intense tasks. But there was a lot going on in my head, as is usual for programming. After coming home starving the first few days, I realized I needed to up my energy intake. In the end, it had nearly doubled… and I still felt hungry sometimes.
Bottom line is, the brain is also like a muscle. It uses up more resources as it becomes more intensely used. Take good care of its needs!