Better loosen your seat belts.

Flyers inhale an estimated 3,400 calories between check-in at the airport and arriving at their destination, according to research on British travelers cited in a a new book, “Gastrophysics: The New Science Behind Eating.”

“The lower cabin air pressure, dry cabin air and the loud engine noise all contribute to our inability to taste and smell food and drink,” the book’s author, Professor Charles Spence, a lecturer at Oxford University, told Telegraph Travel. “[Therefore] the food we consume needs 20-30% more sugar and salt to make it taste like it would on the ground.”

Spence adds that boredom plays a role too — “with nothing else to do, food becomes an appealing distraction” — as does the movies and TV we’re watching mid-air. “It is not uncommon to find people eating as much a third more food with the TV on,” he tells Telegraph Travel.

Whatever the reasons, 3,400 calories is more than most people should be eating in an entire day. While this varies based on age, activity level and gender, even an active teenage man shouldn’t eat than 3,200 calories in a day. And for a person with a more sedentary life, roughly 2,000 is all they should nibble on.

If you’re saying to yourself “but I’ll burn those calories off while I’m on vacation,” don’t kid yourself. A study published last year in the journal Physiology & Behavior found that Americans who go on vacation for one to three weeks at a time gain roughly ⅓ of a pound while they’re there. And while that number may not sound like a lot, the researchers think that it may contribute to weight gain of 0.9 – 2.2 pounds per year.

The good news: You can eat healthfully on the plane with some advance planning. Pack food ahead of time and bring it with you or, barring that, buy things like fruit in the airport to bring with you on the plane. Many airlines also offer snack boxes that list the calories, salt and sugar content, so you can make more informed choices.