Our brain relies on glucose from the blood to function more so than almost any other organ. When we haven't had a nutritious meal in a while, blood glucose levels decrease to the point where mind tasks become more difficult than with a satisfied stomach (does the phrase ‘fat and happy' ring a bell?) You probably won't lose motor function or forget how to tell time while you're waiting to go on your lunch break, but there is a good chance that you'll become more short-tempered with your colleagues and family members. Since glucose supplies are low, your brain is subsequently allocating the available resources to vital functions, making simple, less important tasks (like following social norms - being nice to people) more difficult.
The brain also releases certain hormones in response to low glucose levels. Cortisol and adrenaline are two of those hormones, both of which are also released by the brain under other conditions of stress not related to hunger. Sometimes our body can't tell the different between hunger-related stress and danger-related stress, though, so an increase of these hormones in your bloodstream might cause you to lash out more so than you might after a satisfying meal.
In addition to resource allocation and hormone-related explanations, another reason you get "hangry" is because hunger and anger actually share some genes that regulate these feelings. Neuropeptide Y constricts blood vessels when released and is involved in blood pressure regulation and angiogenesis (development of new blood vessels), according to the National Institutes of Health (NIH). In addition, it regulates eating behavior by increasing a person's appetite (NIH).
Although the connection between hunger and anger is often laughed about and someone might tease you about just being hungry when you're in a bad mood, it is admittedly a characteristic that must be selected for during the process of natural selection. If we were passive about getting the nutrients we need to live through consuming daily meals, we wouldn't be strong or able to survive.
So, the next time someone teases you about being "hangry," boldly state that you are simply playing your part in survival of the fittest - or the hungriest.
Check out this Snickers commercial that puts a comedic spin on the "hangry" phenomenon - have you ever felt the burden of "hanger?"
Source: CNN