The five food and drinks you need to avoid while flying.

When boarding a long-haul flight with hours and hours of spare time ahead of you, there are two invariable certainties: one, you will watch a lot of movies, and two you will eat more of the in-flight food than you ever thought possible.

And while we’ve known for some time now what to avoid before flying, it turns out there’s actually quite a few food groups you should steer clear of mid-flight as well if you want to have a comfortable flight.

Coming in at number one is caffeine, which is hardly surprising given how dehydrating it is. What that means in terms of air travel, though, is no tea, no coffee, no tiramisu or caffeinated soft drinks. Your best bet, Skyscanner Australia says, is water, and lots of it.

Perhaps more surprisingly, though, are cruciferous vegetables (cauliflower, broccoli, kale, bok choy, Brussell sprouts, cabbage) which, while great in your everyday two-feet-on-the-ground life, are likely to play havoc when you're flying due to being high in complex carbohydrates.

Oh my, what a shame.

Unable to break down in the small intestines, eating cruciferous vegetables can lead bloating and cramps when hitting the large intestines. It's the kind of pain that is even less desirable than sharing your seat row with a snorer, really.

Next up is alcohol, the culprit for everyone's bad behaviour both on solid ground and in the air. Aside from turning you into a slurring hot mess, consuming alcohol while flying will also leave you seriously parched and desperately reaching for more water.

Another flying favourite that we're sad to see scratched from the okay to eat list is salty foods. No more crisps, salted nuts or pretzels for you. They're tempting, for sure, but all these tiny packaged little devils will do is help you retain water, bloat you out and leave you hungry for more food. And on a long-haul flight, that's something you're surely keen to avoid.

The final banned beverage, which should come as no surprise, is fizzy and carbonated drinks. Not only are they filled with sugar which will jack you to the wazoo and leave you with nowhere to go and exert that newfound energy, they'll also wreak havoc on your gastrointestinal tract and leave you bloated and struggling to sleep.