Every time we ingest food, the carbohydrates, proteins, and fats are broken down into simple sugars (such as glucose), free fatty acids, and amino acids. These nutrients are then distributed throughout the body where they are most needed.
After a snack or meal, the amount of glucose in our bodies is high. This is generally a good thing because our brains rely on glucose as their main source of energy. Without a steady amount of glucose moving through the bloodstream to the brain, even small tasks can become difficult and we may experience “brain fog,”—in other words, difficulty concentrating on work or coming up with ideas.
Since the brain is critically dependent on glucose to function, our bodies start to panic when glucose levels drop after we haven’t eaten for an extended period of time. The amount of time it takes for our bodies to respond to these low levels depends on what and how much we last ate—but the exact results can vary from person to person. When a certain low level of glucose in the bloodstream is reached, our brain perceives this as a life-threatening problem and sends out a panic signal to the rest of the body.
The body hears the brain’s warning and releases hormones that raise our blood sugar to emphasize that we need to eat. Cortisol, a stress hormone, and adrenaline, the fight-or-flight hormone, are also released amidst this cascade of hormones. These are the same two hormones that would be released if a bear was chasing us or if we were directed to give an impromptu speech, so feeling cranky isn’t a completely bizarre side effect. “Hangry” is a fairly accurate description of what’s going on inside us in this scenario.
To add to the stomach-brain connection, it turns out that genes control our joint anger and hunger responses. One of these genes creates a protein called neuropeptide Y, which regulates anger and stimulates eating behavior. Our desire for food increases along with our frustration and anger.