Image copyright Reuters Image caption Chloe Kim has tweeted about ice cream and churros (fried dough) during the Winter Olympics

Chloe Kim was 'hangry' before winning a Winter Olympic gold medal. So why does hunger make people angry?

On Tuesday morning in South Korea, a 17-year-old American sent a tweet about her breakfast. Within minutes, it had flown round the world.

"Wish I finished my breakfast sandwich but my stubborn self decided not to," wrote the teenage snowboarder Chloe Kim.

"And now I'm getting hangry."

Kim's admission of being hangry - hungry and angry - struck a chord. The tweet was liked 88,000 times - and counting.

Being hangry, however, didn't do Kim any harm. Her next tweet, sent three hours later, showed her celebrating a gold medal.

What causes hanger?

In essence, it's a survival mechanism. Here's Dr Michael Knight, assistant professor of medicine at George Washington University School of Medicine and Health Sciences.

"When we eat a meal, our body breaks down the food into nutrients such as glucose - a simple sugar that our body uses for energy," he says.

"Our brain is one of the largest consumers of that energy. About 20-25% of our total energy is consumed by our brain - which is only about 2% of our body weight.

"Hunger is a signal that the brain needs more fuel. It's triggered when the level of nutrients in our bloodstream begins to drop.

"When the brain runs dry of fuel, it stimulates a stress response. It's really a survival mechanism.

"Our inhibition to different emotions is lowered. And - because the brain needs fuel to function at its highest capacity - we see things like difficulty concentrating, and difficulty controlling emotions.

"One of the most common emotions is anger - and that's why, many times, when we become hungry, we become irritable."

How can you stop hanger?

"If you have a full meal, with balanced nutrients, that's going to hold you over to the next meal," says Dr Knight.

"If you start feeling hanger coming on, something that's a little bit sweeter - something that gets you that glucose - is going to quickly reverse that feeling."

So - as the adverts suggest - a chocolate bar could do the trick?

"There's actually some science behind it," he says.

"If you're getting that sugar, it's increasing your glucose level, your brain is feeling the fuel, and it's decreasing that stress response."

Media playback is unsupported on your device Media caption Winter Olympics 2018: USA's Chloe Kim dominates for gold

Are carbohydrates, such as sugar, better for a quick-fix?

"It's mainly carbohydrate that we're breaking down into glucose," says Dr Knight.

"Our body does have a way of breaking down other foods [fats and proteins] and making more glucose - especially in those who are not eating that many carbohydrates.

"But the quickest way to get to glucose is by eating carbohydrate."

So, in short: Kim should have finished her sandwich.

Do genetics play a part?

"One individual may be able to go quite some time without feeling irritable," says Dr Knight. "While some others, as soon as they stop eating, it seems they're ready to snap."

Dr Knight says "we don't fully understand the genetics behind" the process. But some of the important chemicals, such as Neuropeptide Y, are genetically linked to DNA.

"So it just may be that, because of your genetics, and your control of emotions, you may be predisposed to developing hanger."

Image copyright George Washington University Medical Faculty Assoc Image caption Michael Knight, MD, assistant professor of medicine at the George Washington University School of Medicine and Health Sciences

Do women suffer more from hanger?

"It's something we're still learning about," he says. "But there's nothing that says women are this percentage, or that percentage, more likely to have it.

"It can really vary from person to person, as hunger does."

But hanger is definitely a real thing?

"Definitely," says Dr Knight.

"I work in a weight management practice at George Washington University. It's very common for patients to have this feeling, and that leads to them eating a lot more.

"That's something we have to work with them to address."

The word has even been recognised by the Oxford English Dictionary. Last month, it announced that "hangry" was a real word, defined as "bad-tempered or irritable as a result of hunger".

Happily for Chloe Kim, her hanger didn't last long. After winning gold, she was seen tucking into a tub of ice cream.