Let's start with stress eating.
According to science, when people get stressed out, they "turn to hyperpalatable comfort foods such as fast food, snacks, and calorie-dense foods, even in the absence of hunger and lack of homeostatic need for calories," according to a study conducted by Yale University researchers.
You know what's stressful? Taking cell-phone video of a guy getting roughed up on an airplane. Listening to your pilot come unhinged over the intercom. Being Ann Coulter. We could go on, but we don't want to contribute to your stress eating.
The point is: Commercial air travel is inherently stressful. Even more noteworthy: When we fly, we eat like there's no tomorrow.
In fact, a commercial flight is the perfect storm of mindless munching. The urge to snack en route seems to be universal, but stress isn't the only culprit. Here are a few more factors that give you Cookie Monster–level desire for empty calories when you fly.
Flying is boring. Food is not.
Even in the days before we associated commercial flights with terrorism, increasingly smaller seats, and meal deprivation, we have to imagine it wasn’t ever exactly fun to fly. For passengers, once you make it through security, cram your carry-on overhead, and find your seat, flying is essentially just sitting in a cramped chair for a few hours. No fun.
Cell phones exist, so the age of boredom is supposed to be over, but have you ever tried to use the in-flight wifi? It is slow. It is unreliable. In fact, air travel pretty much proves that boredom can't be defeated.
Your first flight is pretty amazing; you are hurtling through the air and it's incredible.
Pretty soon, though, things get mundane. The "fasten seatbelt" light gets boring. The crew's preparation for gate departure gets boring. Placing your seatbacks and tray tables in their full, upright positions gets boring.
And boredom is a one-way ticket to Snack Town (service by Delta, United, and American, so pick your poison). A 2012 study from the journal Health Psychology concluded that "boredom is an important construct and ... should be considered a separate dimension of emotional eating."
In short, people tend to snack when they're bored, and people tend to be bored on airplanes. You do the math.
Flying dehydrates us, and we are no good at telling the difference between thirst and hunger.
After a long flight, you might sense that your dry skin is out of control. That's not just your imagination. In fact, the air you breathe during a flight has to come from somewhere.
Specifically, it has to come from outside. But the air outside an airplane is very different from the air you're breathing right now (unless you're lucky enough to have in-flight wifi that actually works).
At 30,000 feet, the air essentially freeze-dries itself. It's so cold that the airplane has to warm it on its way into the cabin. This heating process quickly robs the air of most of the moisture it otherwise would’ve had.
According to the World Health Organization, humidity in airplane cabins is usually below 20 percent. By way of comparison, if you're reading this in your house, the humidity is probably more than 30 percent.
Getting dried out can make you thirsty, and thirst mimics the symptoms of hunger. Danyale McCurdy-McKinnon, clinical psychology director of the Fit for Healthy Weight Clinic at the University of California, Los Angeles, told TODAY that you should make sure you're drinking enough before starting to nosh.
"If it's only been a couple of hours since you've eaten and you feel hungry, try drinking some water first," McCurdy-McKinnon said. "And if you still feel hungry then have a snack."
So say yes to that ginger ale or tomato juice that your flight attendant so politely offers you. In fact, try the tomato juice. Oddly enough, science suggests that it tastes better in the air than it does on the ground.
Things taste different above the clouds.
Not long ago, the German airline Lufthansa noticed something peculiar. They were serving something like 53,000 gallons of tomato juice every year, far more than they'd expect. What gives? The executives asked.
According to an NBC news report, Lufthansa hired a research company called the Fraunhofer Society to figure out why people chug so much tomato juice on airplanes. It's not like tomato juice is a favorite on the ground. What changes up in the air?
To find out, researchers from the Fraunhofer Society sent their subjects into a super-realistic flight simulator housed in the dismembered fuselage of an old jet. The researchers recreated the environment of an airplane at cruising altitude—complete with cabin pressure—and served beverages including tomato juice.
Most of the subjects agreed: The tomato juice was way better up there than it was down on the ground.
"We learned that tomato juice being on ground level is rather—I'm not saying moldy, but it tastes earthy, it tastes not overly fresh," Ernst Derenthal, Lufthansa's catering executive, told NBC. "However, as soon as you have it at 30,000 feet, tomato juice shows, let's say, its better side. It shows more acidity, it has some mineralic taste with it, and it's very refreshing."
Okay, so people like tomato juice on airplanes, but there's more than altitude at work here.
The NBC report attributes people's love of airplane V8 to the dampening effect that flying has on the taste buds. In low pressure, your taste buds get a little less oxygen than they're used to and lose a little sensitivity. Plus, the low humidity dries out your mouth, further diminishing your sense of taste. Tomato juice just happens to be one of the beverages that actually benefits from less-sensitive taste buds.
A 2015 study from Cornell University suggests an even weirder explanation: The sound of the engines makes us crave umami, a savory flavor that tomato juice offers in abundance.
But we're not just talking about tomato juice. Maybe people like to snack on planes because their taste buds act so differently—maybe it's all a big, semi-conscious experiment. What does a pretzel taste like in the air? A strawberry? Could they be as good as tomato juice seems to have become?
One more word about tomato juice: Derenthal suggests one more reason people order it so often on airplanes.
"Many people, they have not made their minds up, and just wonder, 'What should I drink? In two minutes I will be asked by the flight attendants,'" Derenthal said. "And then you see someone in front of you having a tomato juice and you think, 'Why not? That's a good idea. Oh, I'll have the same as the gentleman in the other row.'"
Other people on airplanes snack. Why should we resist?
Of course, the real reason that we gobble everything in sight as we hurtle through the clouds might be really simple. It could just be that everyone around us is already doing it. We're social animals. We're impressionable—especially when it comes to comestibles.
A 2014 literature review from the Journal of the Academy of Nutrition and Dietetics suggests that other people's dining habits rub off on us easily.
The authors looked at 15 experimental studies and concluded that not only do the dining choices of peers affect what we eat, but we don't even have to see them eating to get the effect. They can just tell us about what they eat.
"The evidence reviewed here is consistent with the idea that eating behaviors can be transmitted socially," Eric Robinson, the study's lead investigator, said in a press release.
In other words, when your neighbor asks for extra peanuts, you might make the same request.
Add up all of the above factors and it's a wonder we don't gorge ourselves even more when we fly. Fortunately, the peanut and pretzel packages are very small. Maybe that's not the airlines cutting corners again—maybe they really are looking out for their customers.