Why do people get a headache from not eating?

You brain is thinking all the time but your brain needs to feed off of something to think so you get head ache from thinking but not feeding your brain.

For me it's the opposite

Because your blood sugar gets too low. #PersonalExperience

My hypothsis is because you become dehydrated when you don't have food, so I'm guessing the fluid is running out your body. Don't count this as a complete answer though, its just a hypothesis from knowledge.

It's your body telling you: IM HUNGRY GIMME FOOD!

Yep