OxfordDictionaries.com explains the word "hangry" this way:
It is only in the 21st century that the word hangry, a blend of hungry and angry used colloquially to mean ‘bad-tempered or irritable as a result of hunger’, has entered common use. However, the earliest known evidence for the word dates from 1956, in an unusual article in the psychoanalytic journal American Imago that describes various kinds of deliberate and accidental wordplay.
As a noun for being hangry, the word "hanger" can work when spoken with a hard g, but in print it is too confusing , so here I'll nominalize "hangry" to "hangriness." (The other alternative is "hangry" as a noun as well as an adjective.)
Hangriness is a real thing. The Wall Street Journal's Heidi Mitchell interviewed Michael Lowe, a psychologist interested in eating disorders for an August 29, 2018 article:
The popularity of the term hangry has outstripped the scientific research on it, Dr. Lowe says. He agrees that food deprivation can contribute to “a hypersensitivity to react to things you wouldn’t react to much or at all when you’re not hungry.” However, food deprivation exacerbates other feelings, too. “If we had a list of 10 negative emotions, my guess is that as people get hungrier, the scores of most of the negative emotions would go up, not just anger,” he says.
Just after we begin eating, blood-sugar levels rise sharply, then gradually decline for hours until we eat again. “At some point, one starts to experience falling glucose levels and stomach growling and other signs of energy deprivation that trigger an alarm in the brain,” Dr. Lowe says.
Some of the best evidence for the reality of hangriness or the broader set of psychological effects of low blood sugar is from three business school professors: Shai Danziger, Jonathan Levav, and Liora Avnaim-Pesso. Michael Lowe summarizes their Proceedings of the National Academy of Science of the USA article "Extraneous factors in judicial decisions" as follows:
Dr. Lowe also points to a study of eight Israeli judges who granted 65% of convicts’ parole requests in the morning and after a snack break, but almost none at day’s end. “Someone who is very hungry and irritable is likely to react more harshly” than his or her well-fed co-worker, he says.
Michael Lowe knows something about the effects of being hangry. And I don't doubt that it is a reflection of low blood sugar. But Michael is not as clued in as he should be about the causes of low blood sugar. As I wrote in "How Sugar Makes People Hangry":
A big cause of low blood sugar is when you have eaten sugar, refined carbs or some other food with a high insulin index a couple of hours earlier. When sugar, refined carbs or something else high on the insulin index causes insulin to spike, that insulin causes blood sugar to be removed from the bloodstream (some to the muscles and some to be stored as fat in the fat cells). It is like waking up from being asleep at the wheel, seeing you are drifting off to the right, and then overcorrecting to the left.
So, a good way to reduce the chances of blood sugar low enough to make you "hangry" is to avoid sugar, refined carbs and other foods high on the insulin index.
On the insulin index, see "Forget Calorie Counting; It's the Insulin Index, Stupid." My own experience, and that of others, is that when they eat low on the insulin index, they can go 24 hours without eating without getting hangry. So Michael is assuming a currently customary high-insulin-index diet when he told Heidi Mitchell (in her paraphrase):
There’s everyday hunger people feel five hours or so after a meal, called homeostatic hunger. There’s also hedonic hunger, which happens to some people because they become accustomed to eating simply for pleasure, so they often think about food.'
What Michael calls everyday homeostatic hunger comes on much sooner (five hours in his telling) and is much stronger for all but a minority of people these days because they are eating sugar, easily digestible carbs and other foods high on the insulin index.
Michael mentioned the Minnesota Starvation Experiment, but missed one of the main messages of that experiment:
He cites the famous 1945 Minnesota Starvation Experiment as an extreme example: Of the male volunteers who lost 25% of their body weight in six months, most reported irritability and a decrease in mental ability.
A key to understanding why the experience of men in this experiment was so horrible is what they were eating—carbs high on the insulin index:
Their diet consisted of foods widely available in Europe during the war, mostly potatoes, root vegetables, bread and macaroni.
If they had been eating a diet low in easily digestible carbs—or eating nothing—they could have made up for fewer food calories by burning their own fat without much discomfort, as long as they had a reasonable amount of body fat left. (In the Stanford DIETFITS study I talk about in "Why a Low-Insulin-Index Diet Isn't Exactly a 'Lowcarb' Diet" and "Against Sugar: The Messenger and the Message" people replaced easily digestible carbs with either complex carbs like vegetables or with dietary fat. Either diet worked well.)
Michael's lack of understanding of the role of easily digestible carbs in causing low blood sugar also leads him astray in the stories he tells about our ancestors. Eating in an era before processed foods, before humans had come across potatoes in the Americas, and before grain was domesticated, I argue they would have gotten hangry mainly when their stores of body fat ran low, not when they simply had to go a few days without food while they had plenty of body fat left—a genuinely dangerous and often desperate situation. But processed foods, potatoes and grain have made us feel desperate for food in situations that aren't really desperate at all. (On processed food, see my post "The Problem with Processed Food.")
Not understanding the role of easily digestible carbs and other foods high on the insulin index in hangriness, Michael gives bad advice:
To avoid feeling hangry, Dr. Lowe recommends distributing food intake evenly across the day.
I talk about formal and informal evidence that substantial periods of time with no food are a key to relatively painless weight loss in these posts, among others:
You don't need to snack constantly to avoid feeling hangry. Just avoid easily digestible carbs and other foods high on the insulin index. And if despite this claim, you are worried you might feel hangry, you can carry around some nuts anywhere in a ziploc bag (but don't go for cashews or peanuts, neither of which are true nuts and both of which have problems). See "Our Delusions about 'Healthy' Snacks—Nuts to That!" That can also help you deal with temptations, as I point out in "Letting Go of Sugar."
The bottom line is that if you feel hangry with any frequency, it is an urgent sign that you need to fix your diet. There are many other reasons to feel negative emotions, including anger, but human beings weren't meant to feel seriously hangry except in genuinely desperate situations. If you do feel hangry with any frequency, take it as a sign you are probably eating badly.
Don't miss these other posts on diet and health and on fighting obesity:
Julia Belluz and Javier Zarracina: Why You'll Be Disappointed If You Are Exercising to Lose Weight, Explained with 60+ Studies (my retitling of the article this links to)
Also see the last section of "Five Books That Have Changed My Life" and the podcast "Miles Kimball Explains to Tracy Alloway and Joe Weisenthal Why Losing Weight Is Like Defeating Inflation." If you want to know how I got interested in diet and health and fighting obesity and a little more about my own experience with weight gain and weight loss, see my post "A Barycentric Autobiography."