The science of 'hangry:' Why some people get grumpy when they're hungry

A man expresses disapproval at his friend's table manners as she sinks her teeth greedily into a sandwich, circa 1940.

Story highlights

  • The answer lies in the body's reaction to needing food
  • If blood-glucose levels fall far enough, your brain perceives it as a life-threatening situation

National Health and Medical Research Council senior research fellow in the Boden Insitute of Obesity, Nutrition, Exercise & Eating Disorders at University of Sydney. The opinions expressed in this commentary are solely those of the author. CNN is showcasing the work of The Conversation, a collaboration between journalists and academics to provide news analysis and commentary. The content is produced solely by The Conversation.

(CNN)Have you ever snapped angrily at someone when you were hungry? Or has someone snapped angrily at you when they were hungry? If so, you've experienced "hangry" (an amalgam of hungry and angry) -- the phenomenon whereby some people get grumpy and short-tempered when they're overdue for a feed.

But where does hanger come from? And why is it that only some people seem to get hangry? The answer lies in some of the processes that happen inside your body when it needs food.

    The physiology of hanger

    The carbohydrates, proteins and fats in everything you eat are digested into simple sugars (such as glucose), amino acids and free fatty acids. These nutrients pass into your bloodstream from where they are distributed to your organs and tissues and used for energy.
    As time passes after your last meal, the amount of these nutrients circulating in your bloodstream starts to drop. If your blood-glucose levels fall far enough, your brain will perceive it as a life-threatening situation. You see, unlike most other organs and tissues in your body which can use a variety of nutrients to keep functioning, your brain is critically dependent on glucose to do its job.
    You've probably already noticed this dependence your brain has on glucose; simple things can become difficult when you're hungry and your blood glucose levels drop. You may find it hard to concentrate, for instance, or you may make silly mistakes. Or you might have noticed that your words become muddled or slurred.
    Another thing that can become more difficult when you're hungry is behaving within socially acceptable norms, such as not snapping at people. So while you may be able to conjure up enough brain power to avoid being grumpy with important colleagues, you may let your guard down and inadvertently